Notes To Financial Statements [Abstract] Notes to Financial Statements [Abstract] Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [Table] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Adjustment Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] As Previously Reported Scenario, Previously Reported [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Accounts receivable, net Accounts Receivable, Net, Current Deferred tax assets Deferred Tax Assets, Net of Valuation Allowance, Noncurrent Other assets Other Assets, Noncurrent Accrued liabilities Accrued Liabilities, Current Deferred revenues Deferred Revenue, Current Retained earnings Retained Earnings (Accumulated Deficit) Revenue remaining performance obligation Revenue, Remaining Performance Obligation Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Expected timing Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected dividends Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Weighted average fair value at grant date (USD per Share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Accounting Standards Update 2016-18 Accounting Standards Update 2016-18 [Member] Adjustment Restatement Adjustment [Member] Initial Application Period [Line Items] Other investing activities Payments for (Proceeds from) Other Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Effect of foreign exchange rate changes on cash, cash equivalents, and restricted cash Effect of Exchange Rate on Cash and Cash Equivalents Net decrease in cash, cash equivalents, and restricted cash Cash and Cash Equivalents, Period Increase (Decrease) Cash, cash equivalents, and restricted cash at beginning of the period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents, and restricted cash at end of the period Disclosure Net Revenues By Geographic Area [Abstract] Disclosure - Net Revenues by Geographic Area [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Statement, Geographical [Axis] Geographical [Axis] Segment, Geographical [Domain] Geographical [Domain] United States UNITED STATES The Netherlands NETHERLANDS China CHINA Other International Other International [Member] Other International [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Net revenues Revenue, Net Investments, Debt and Equity Securities [Abstract] Derivative [Table] Derivative [Table] Currency [Axis] Currency [Axis] All Currencies [Domain] All Currencies [Domain] Euro Euro Member Countries, Euro Chinese Yuan China, Yuan Renminbi Canadian Dollar Canada, Dollars British Pound United Kingdom, Pounds Japanese Yen Japan, Yen Brazilian Real Brazil, Brazil Real Australian Dollar Australia, Dollars Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 2 Fair Value, Inputs, Level 2 [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Prepaid expenses and other current assets Prepaid Expenses and Other Current Assets [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Foreign Exchange Forward Foreign Exchange Forward [Member] Derivative [Line Items] Derivative [Line Items] Gain on foreign currency forward contracts Derivative, Gain on Derivative Notional amount Derivative Asset, Notional Amount Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Certain Distributors Certain Distributors [Member] Certain Distributors [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Cash consideration Payments to Acquire Businesses, Gross Net tangible liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Intangibles acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Goodwill and intangible assets, net Goodwill Statement of Comprehensive Income [Abstract] Net income Net Income (Loss) Attributable to Parent Net change in foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Change in unrealized gains (losses) on investments, net of tax Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Other comprehensive (loss) income Other Comprehensive Income (Loss), Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Disclosure Activity Under Stock Option Plans [Abstract] Disclosure - Activity Under Stock Option Plans [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Number of Shares Underlying Stock Options Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding as of December 31, 2017 Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Cancelled or expired Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Outstanding as of September 30, 2018 Vested at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number Exercisable at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted Average Exercise Price per Share Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Outstanding as of December 31, 2017 Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Exercised Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Cancelled or expired Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Outstanding as of September 30, 2018 Vested at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price Exercisable at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Weighted Average Remaining Contractual Term Share Based Compensation Arrangement By Share Based Payment Award Options Weighted Average Remaining Contractual Term [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Remaining Contractual Term [Abstract] Outstanding as of September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Vested at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term Exercisable at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Share Based Compensation Arrangement By Share Based Payment Award Options Aggregate Intrinsic Value [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value [Abstract] Outstanding as of September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Vested at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value Exercisable at September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Disclosure Segments And Geographical Information Additional Information [Abstract] Disclosure - Segments and Geographical Information - Additional Information [Abstract] Number of reportable segments Number of Reportable Segments Income Statement [Abstract] Cost of net revenues Cost of Revenue Gross profit Gross Profit Operating expenses: Operating Expenses [Abstract] Selling, general and administrative Selling, General and Administrative Expense Research and development Research and Development Expense Total operating expenses Operating Expenses Income from operations Operating Income (Loss) Interest income Interest Income, Operating Other income (expense), net Nonoperating Income (Expense) Net income before provision for income taxes and equity in losses of investee Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Provision for income taxes Income Tax Expense (Benefit) Equity in losses of investee, net of tax Income (Loss) from Equity Method Investments Net income Net income per share: Earnings Per Share [Abstract] Basic (in usd per share) Earnings Per Share, Basic Diluted (in usd per share) Earnings Per Share, Diluted Shares used in computing net income per share: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Disclosure Segment Information [Abstract] Disclosure - Segment Information [Abstract] Business Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Operating segments Other Segments [Member] Clear Aligner Clear Aligner [Member] Clear Aligner [Member] Scanner Scanners And Services [Member] Scanners and Services [Member] Unallocated corporate expenses Corporate and Other [Member] Gross profit Income from operations Depreciation and amortization Depreciation, Depletion and Amortization Other income (expense), net Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] SDC SDC [Member] SDC [Member] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Ownership Equity Method Investment, Ownership Percentage Payments to acquire Payments to Acquire Equity Method Investments Additional ownership acquired Equity Method Investment Ownership Acquired Equity Method Investment Ownership Acquired Equity method investments Equity Method Investments Due from related parties Due from Related Parties Loan receivable Loans and Leases Receivable, Commitments, Fixed Rates Loan repayment from equity investee Proceeds from Collection of Loans Receivable Disclosure Total Estimated Annual Future Amortization Expense For Acquired Intangible Assets [Abstract] Disclosure - Total Estimated Annual Future Amortization Expense for Acquired Intangible Assets [Abstract] Remainder of 2018 Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Five Thereafter Future Amortization Expense Thereafter Future Amortization Expense, Thereafter Net Carrying Value, ending balance Finite-Lived Intangible Assets, Net Credit Facilities Debt Disclosure [Text Block] Stockholders' Equity Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Fair Value Disclosures [Abstract] Equity securities under the equity method investment Equity securities without readily determinable fair values Securities Owned Not Readily Marketable Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Fair Value Hierarchy [Domain] Level 3 Fair Value, Inputs, Level 3 [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Short-term notes receivable Notes Receivable [Member] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Short-term notes receivable Notes Receivable, Fair Value Disclosure Investments and Fair Value Measurements Financial Instruments Disclosure [Text Block] Summary of Goodwill by Reportable Segment Schedule of Goodwill [Table Text Block] Schedule of Amortized Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Finite-Lived Intangible Assets, Future Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Disclosure Intangible Assets As Direct Result From Cadent Acquisition [Abstract] Disclosure - Intangible Assets as Direct Result from Cadent Acquisition [Abstract] Schedule of Finite-Lived Intangible Assets by Major Class [Table] Schedule of Finite-Lived Intangible Assets [Table] Acquired Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Trademarks Trademarks [Member] Existing technology Existing Technology [Member] Existing Technology [Member] Customer relationships Customer Relationships [Member] Reacquired rights Distribution Rights [Member] Patents Patents [Member] Other Other Intangible Assets [Member] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Weighted Average Amortization Period (in years) Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Gross Carrying Amount, beginning balance Finite-Lived Intangible Assets, Gross Accumulated Amortization Finite Lived Intangible Assets Accumulated Amortization Period Increase Decrease Finite-Lived Intangible Assets, Accumulated Amortization, Period Increase (Decrease) Accumulated Impairment Loss Finite-Lived Intangible Assets, Accumulated Impairment Loss Finite-Lived Intangible Assets, Accumulated Impairment Loss Disclosure Summary Of Nonvested Shares [Abstract] Disclosure - Summary of Nonvested Shares [Abstract] Award Type [Axis] Award Type [Axis] Award Type [Domain] Equity Award [Domain] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Number of Shares Underlying RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Nonvested as of December 31, 2017 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vested and released Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Nonvested as of September 30, 2018 Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Nonvested as of December 31, 2017 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Vested and released Sharebased Compensation Arrangement By Sharebased Payment Award Equity Instruments Other Than Options Vested And Released In Period Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options Vested And Released In Period Weighted Average Grant Date Fair Value Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Nonvested as of September 30, 2018 Weighted Remaining Contractual Term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Nonvested as of September 30, 2018 Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Outstanding Weighted Average Remaining Contractual Term 1 Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Outstanding Weighted Average Remaining Contractual Term 1 Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value [Abstract] Nonvested as of September 30, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Schedule Of Earnings Per Share Basic And Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Net income Weighted-average common shares outstanding, basic Dilutive effect of potential common stock Weighted Average Number Diluted Shares Outstanding Adjustment Total shares, diluted Net income per share, basic Net income per share, diluted Short-Term And Long-Term Marketable Securities Available-for-sale Securities [Table Text Block] Investments Classified by Contractual Maturity Date Investments Classified by Contractual Maturity Date [Table Text Block] Investments in privately held companies Cost and Equity Method Investments [Table Text Block] Cost and Equity Method Investments [Table Text Block] Financial Assets Measured At Fair Value On Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Notional value of derivative instruments Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Capitalized commissions Capitalized Contract Cost, Net Equity securities Security deposits Security Deposit Loan receivable from equity investee Loans Receivable, Net Other long-term assets Other Long-term Assets Other Long-term Assets Total other assets Disclosure Common Stock Repurchase Program Additional Information [Abstract] Disclosure - Common Stock Repurchase Program - Additional Information [Abstract] Share Repurchases [Table] Share Repurchases [Table] Share Repurchases [Table] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] April 2014 Stock Repurchase Program April 2014 Stock Repurchase Program [Member] April 2014 Stock Repurchase Program [Member] April 2016 Repurchase Program April 2016 Repurchase [Member] April 2016 Repurchase [Member] 2017 ASR 2017 Stock Repurchase Program [Member] 2017 Stock Repurchase Program [Member] May 2018 Repurchase May 2018 Repurchase [Member] May 2018 Repurchase [Member] Share Repurchases [Line Items] Share Repurchases [Line Items] Share Repurchases [Line Items] Accelerated share repurchase (shares) Stock Repurchased and Retired During Period, Shares Share repurchase price (in dollars per share) Treasury Stock Acquired, Average Cost Per Share Price ($ per share) Accelerated Share Repurchases, Final Price Paid Per Share Repurchased Stock Repurchased and Retired During Period, Value Repurchase of common stock, common stock authorized Stock Repurchase Program, Authorized Amount Remaining shares under repurchase program Stock Repurchase Program, Remaining Authorized Repurchase Amount Disclosure Credit Facilities Additional Information [Abstract] Disclosure - Credit Facilities - Additional Information [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Minimum Minimum [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Base Rate Base Rate [Member] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Line of credit, available borrowings Line of Credit Facility, Maximum Borrowing Capacity Current borrowing capacity Line of Credit Facility, Current Borrowing Capacity Basis Spread on Variable Rate Debt Instrument, Basis Spread on Variable Rate Outstanding borrowings Long-term Line of Credit Disclosure Stockbased Compensation Additional Information [Abstract] Disclosure - Stock-based Compensation - Additional Information [Abstract] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Cost of net revenues Cost of Sales [Member] Selling, general and administrative Selling and Marketing Expense [Member] Research and Development Expense [Member] Research and Development Expense [Member] Employee Stock Purchase Plan 2010 Employee Stock Purchase Plan 2010 [Member] Employee Stock Purchase Plan, 2010 [Member] Market Performance Based Restricted Stock Units Market Performance Based Restricted Stock Units [Member] Market Performance Based Restricted Stock Units [Member] Employee Stock Purchase Plan Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Axis] Schedule Of Share Based Compensation Arrangement By Share Based Payment Award [Axis] Schedule of Share-based Compensation Arrangement by Share-based Payment Award [Axis] Share-based Compensation Arrangements by Share-based Payment Award [Domain] Share Based Compensation Arrangements By Share Based Payment Award [Domain] Share-based Compensation Arrangements by Share-based Payment Award [Domain] Incentive Plan 2005 Stock Incentive Plan 2005 [Member] 2005 Stock Incentive Plan [Member] Shares reserved for issuance Common Stock, Capital Shares Reserved for Future Issuance Number of shares available for issuance Common Stock, Capital Shares Reserved For Future Issuance, Shares Available Common Stock, Capital Shares Reserved For Future Issuance, Shares Available Total unamortized compensation cost Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average period of total unamortized cost (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Vesting period of granted market-performance based restricted stock units Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Percentage of market-performance based restricted stock units eligible to vest over the vesting period Percentage Of Market Performance Based Restricted Stock Units During Vesting Period Maximum percentage of market-performance based restricted stock units during vesting period. Maximum number of shares available Employee Stock Purchase Plan Number Of Shares Available For Issuance Employee Stock Purchase Plan, Number Of Shares Available for Issuance Number of shares remaining Share Based Compensation Arrangement By Share Based Payment Award Shares Remaining Available For Issuance Share Based Compensation Arrangement By Share Based Payment Award Shares Remaining Available For Issuance Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Business Combinations Business Combination Disclosure [Text Block] Schedule of Future Lease Payments Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Document Documentand Entity Information [Abstract] Document and Entity Information [Abstract] Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Statement of Financial Position [Abstract] Accounts receivable, allowance for doubtful accounts Allowance For Doubtful Accounts Receivable And Sales Returns Current Allowance For Doubtful Accounts Receivable And Sales Returns Current Preferred stock, par value (in usd per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized Preferred Stock, Shares Authorized Preferred stock, shares issued Preferred Stock, Shares Issued Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Equity Method Investments Equity Method Investments and Joint Ventures Disclosure [Text Block] Schedule of Inventories Schedule of Inventory, Current [Table Text Block] Schedule of Other Assets Schedule of Other Assets [Table Text Block] Schedule of Accrued Liabilities Schedule of Accrued Liabilities [Table Text Block] Schedule of Warranty Accrual Schedule of Product Warranty Liability [Table Text Block] Schedule of Deferred Revenues Deferred Revenue, by Arrangement, Disclosure [Table Text Block] Accounting for Income Taxes Income Tax Disclosure [Text Block] Disclosure Short Term And Long Term Marketable Securities [Abstract] Disclosure - Short-Term and Long-Term Marketable Securities [Abstract] Schedule of Fair Value of Separate Accounts by Major Category of Investment [Axis] Investment Type [Axis] Schedule of Fair Value of Separate Accounts by Major Category of Investment, Category [Domain] Investments [Domain] Short-term Investments Short-term Investments [Member] Long-term Investments Long Term Investments [Member] Long Term Investments [Member] Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Axis] Commercial paper Commercial Paper [Member] Corporate bonds Corporate Bonds [Member] Corporate Bonds [Member] U.S. government agency bonds Agency Securities [Member] U.S. government treasury bonds US Treasury and Government [Member] Certificates of deposit Certificates of Deposit [Member] Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gains Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Total available for sale short-term and long-term marketable securities Available-for-sale Securities Deferred revenues - current Deferred revenues - long-term Deferred Revenue, Noncurrent Disclosure Summary Of Financial Assets Measured At Fair Value On Recurring Basis [Abstract] Disclosure - Summary of Financial Assets Measured at Fair Value on Recurring Basis [Abstract] Fair Value, Assets and Liabilities Measured on Recurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring Basis [Table] Fair Value, Assets and Liabilities Measured on Recurring Basis [Table] Level 1 Fair Value, Inputs, Level 1 [Member] Cash Equivalents Cash Equivalents [Member] Restricted Cash and Cash Equivalents, Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents, Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Money market funds Money Market Funds [Member] Corporate bonds Corporate Bond Securities [Member] Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Investments Other assets Other Assets, Fair Value Disclosure Assets, Fair Value Disclosure Assets, Fair Value Disclosure Net Income Per Share Earnings Per Share [Text Block] One year or less Available-for-sale Securities, Current Due in greater than one year Available-for-sale Securities, Noncurrent Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Disclosure Accounting For Income Taxes Additional Information [Abstract] Disclosure - Accounting for Income Taxes - Additional Information [Abstract] Income Taxes [Table] Income Taxes [Table] Income Taxes [Table] Accounting Standards Update 2016-09 Accounting Standards Update 2016-09 [Member] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Foreign Tax Authority Foreign Tax Authority [Member] Income Taxes [Line Items] Income Taxes [Line Items] Income Taxes [Line Items] Effective income tax rate, continuing operations Effective Income Tax Rate Reconciliation, Percent Tax benefit, reversed Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Reversed Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Reversed Income Tax Expense (Benefit), Previously Unrecognized Income Tax Expense (Benefit), Previously Unrecognized Income Tax Expense (Benefit), Previously Unrecognized Unrecognized Tax Benefits, Interest on Income Taxes Expense Unrecognized Tax Benefits, Interest on Income Taxes Expense Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Accrual Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Accrual Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Accrual Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Effective Income Tax Rate Reconciliation Share based Compensation Excess Tax Benefit Amount Unrecognized tax benefits Unrecognized Tax Benefits Accrued penalties and interest Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Extension period Income Tax Extension Period Income Tax Extension Period Foreign income tax rate Effective Income Tax Reconciliation, at Foreign Income Tax Rate Effective Income Tax Reconciliation, at Foreign Income Tax Rate Undistributed earnings of foreign subsidiaries Undistributed Earnings of Foreign Subsidiaries Amount of no longer indefinitely reinvested foreign earnings Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings Of Foreign Subsidiaries, No Longer Indefinitely Reinvested Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings Of Foreign Subsidiaries, No Longer Indefinitely Reinvested Deferred tax liability due in event of foreign earnings being distributed Deferred Tax Liability Not Recognized, Amount That Would Be Due If Earnings Are Distributed Deferred Tax Liability Not Recognized, Amount That Would Be Due If Earnings Are Distributed Amount of indefinitely reinvested foreign earnings Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries Additional income tax expense due to TCJA Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Income Tax Expense (Benefit) Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Income Tax Expense (Benefit) TCJA related to provisional transion tax liability Tax Cuts and Jobs Act of 2017, Transition Tax for Accumulated Foreign Earnings, Liability TaxCutsAndJobsActOf2017TransitionTaxForAccumulatedForeignEarningsLiability TCJA related to remeasurement of certain deferred tax assets and liabilities Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Assets and Liabilities, Income Tax Expense Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Assets and Liabilities, Income Tax Expense Legal Proceedings [Abstract] Legal Proceedings [Abstract] Legal Proceedings Legal Proceedings [Text Block] Legal Proceedings [Text Block] Disclosure Summary Of M S U Performance [Abstract] Disclosure - Summary of MSU Performance [Abstract] Number of Shares Underlying MSUs Weighted Average Remaining Contractual Term (in years) Disclosure Accrued Liabilities [Abstract] Disclosure - Accrued Liabilities [Abstract] Accrued payroll and benefits Employee-related Liabilities, Current Accrued expenses Accrued Expenses Accrued Expenses Accrued fixed assets Accrued Fixed Assets, Current Accrued Fixed Assets, Current Accrued warranty Standard Product Warranty Accrual, Current Accrued professional fees Accrued Professional Fees, Current Accrued sales rebate Accrued Marketing Costs, Current Accrued customer credits Accrued Customer Credits Accrued Customer Credits Accrued sales tax and value added tax Sales and Excise Tax Payable, Current Accrued sales return reserve Accrued Sales Return Reserve, Current Accrued Sales Return Reserve, Current Accrued income taxes Accrued Income Taxes, Current Other accrued liabilities Other Accrued Liabilities, Current Total accrued liabilities ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Marketable securities, short-term Available-for-sale Securities, Debt Securities, Current Accounts receivable, net of allowance for doubtful accounts of $2,611 and $5,814, respectively Inventories Inventory, Net Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Total current assets Assets, Current Marketable securities, long-term Available-for-sale Securities, Debt Securities, Noncurrent Property, plant and equipment, net Property, Plant and Equipment, Net Goodwill and intangible assets, net Intangible Assets, Net (Including Goodwill) Deferred tax assets Total assets Assets LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Total current liabilities Liabilities, Current Income tax payable Taxes Payable Other long-term liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Commitments and contingencies (Notes 8 and 9) Commitments and Contingencies Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Preferred stock, $0.0001 par value (5,000 shares authorized; none issued) Preferred Stock, Value, Issued Common stock, $0.0001 par value (200,000 shares authorized; 79,983 and 80,040 issued and outstanding, respectively) Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive income (loss), net Accumulated Other Comprehensive Income (Loss), Net of Tax Total stockholders’ equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders’ equity Liabilities and Equity Stock-based Compensation Expense Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Stock Option Activity Share-based Compensation, Stock Options, Activity [Table Text Block] Summary Of Restricted Stock Units Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] Summary Of Market-performance Based Restricted Stock Units Schedule of Nonvested Performance-based Units Activity [Table Text Block] Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block] Disclosure Change In Carrying Value Of Goodwill [Abstract] Disclosure - Change in Carrying Value of Goodwill [Abstract] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Clear Aligner Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Balance as of December 31, 2017 Adjustments Goodwill, Translation and Purchase Accounting Adjustments Balance as of September 30, 2018 Common Stock Repurchase Programs Share Repurchase Program Disclosure [Text Block] Share Repurchase Program Disclosure Condensed Balance Sheet Statement [Table] Condensed Balance Sheet Statement [Table] Deferred Revenue Deferred Revenue [Member] Deferred Revenue [Member] Condensed Balance Sheet Statements, Captions [Line Items] Condensed Balance Sheet Statements, Captions [Line Items] Revenue recognized Deferred revenue Contract with Customer, Liability, Revenue Recognized Original maturity of highly liquid investments included in cash and cash equivalents Maturity Period Used To Classify Investments Maturity Period Used to Classify Investments Weighted average maturity Marketable Securities, Weighted Average Remaining Maturity Marketable Securities, Weighted Average Remaining Maturity Segments and Geographical Information Segment Reporting Disclosure [Text Block] Disclosure Long Lived Assets By Geographic Area [Abstract] Disclosure - Long-Lived Assets by Geographic Area [Abstract] Costa Rica COSTA RICA Mexico MEXICO Total long-lived assets Statement of Cash Flows [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Deferred taxes Deferred Income Tax Expense (Benefit) Depreciation and amortization Stock-based compensation Share-based Compensation Equity in losses of investee Other non-cash operating activities Other Noncash Income (Expense) Changes in assets and liabilities, net of effects of acquisitions: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Inventories Increase (Decrease) in Inventories Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Accounts payable Increase (Decrease) in Accounts Payable Accrued and other long-term liabilities Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Long-term income tax payable Increase (Decrease) in Income Taxes Payable Deferred revenues Increase (Decrease) in Deferred Revenue Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Purchase of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Purchase of marketable securities Payments to Acquire Available-for-sale Securities Proceeds from maturities of marketable securities Proceeds from Sale and Maturity of Available-for-sale Securities Purchases of investments in privately held companies Payments To Acquire Investments In Privately Held Companies Payments To Acquire Investments In Privately Held Companies Proceeds from sales of marketable securities Proceeds from Sale of Available-for-sale Securities Loan advances to equity investee Payments to Acquire Loans Receivable Other investing activities Net cash used in investing activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from issuance of common stock Proceeds from Issuance of Common Stock Common stock repurchases Payments for Repurchase of Common Stock Fair value Employees’ taxes paid upon the vesting of restricted stock units Payments Related to Tax Withholding for Share-based Compensation Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Net decrease in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect SUPPLEMENTAL CASH FLOW INFORMATION: Supplemental Cash Flow Information [Abstract] Accounts payable or accrued liabilities related to property, plant and equipment Capital Expenditures Incurred but Not yet Paid Conversion of convertible notes receivable into equity securities Debt Conversion, Converted Instrument, Amount Schedule of New Accounting Pronouncements and Changes in Accounting Principles Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Gain Contingencies, Nature [Axis] Gain Contingencies, Nature [Axis] Gain Contingency, Nature [Domain] Gain Contingency, Nature [Domain] Lawsuit Against 3Shape AS Lawsuit against 3Shape A/S [Member] Lawsuit against 3Shape A/S [Member] Violation Of Trade Laws 3Shape Violation of Trade Laws 3Shape [Member] Violation of Trade Laws 3Shape [Member] Patent Infringement By 3Shape Patent Infringement by 3Shape [Member] Patent Infringement by 3Shape [Member] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] Litigation Status [Axis] Litigation Status [Axis] Litigation Status [Domain] Litigation Status [Domain] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Number of lawsuits/complaints Patent Infringement, Number of Lawsuits Patent Infringement, Number of Lawsuits Patents Allegedly Infringed upon Gain Contingency, Patents Allegedly Infringed upon, Number Disclosure Stock Based Compensation Expense Related To All Stock Based Awards And Employee Stock Purchases [Abstract] Disclosure - Stock-Based Compensation Expense Related to All Stock-Based Awards and Employee Stock Purchases [Abstract] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line [Axis] Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Report Line [Domain] Selling, general and administrative Research and development Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] Stock-based compensation expense Allocated Share-based Compensation Expense Disclosure Warranty Accrual Activity [Abstract] Disclosure - Warranty Accrual Activity [Abstract] Movement in Standard Product Warranty Accrual [Roll Forward] Movement in Standard Product Warranty Accrual [Roll Forward] Balance at beginning of period Standard Product Warranty Accrual Charged to cost of revenues Standard Product Warranty Accrual, Increase for Warranties Issued Actual warranty expenditures Standard Product Warranty Accrual, Decrease for Payments Balance at end of period Basis of presentation Basis of Accounting, Policy [Policy Text Block] Use of estimates Use of Estimates, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Investments in Privately Held Companies Investment, Policy [Policy Text Block] Recent Accounting Pronouncements Recent Accounting Pronouncements [Policy Text Block] Recent accounting pronouncements , Policy [Text Block] Disclosure Inventories [Abstract] Disclosure - Inventories [Abstract] Raw materials Inventory, Raw Materials, Net of Reserves Work in process Inventory, Work in Process, Net of Reserves Finished goods Inventory, Finished Goods, Net of Reserves Total inventories Goodwill and Intangible Assets Disclosure [Abstract] Goodwill impairment Goodwill, Impairment Loss Amortization Amortization of Intangible Assets Disclosure Minimum Future Lease Payments For Non Cancelable Leases [Abstract] Disclosure - Minimum Future Lease Payments for Non-Cancelable Leases [Abstract] Remainder of 2018 Operating Leases Future Minimum Payments Due Remainder Of Period Operating Leases, Future Minimum Payments Due, Remainder of Period 2019 Operating Leases, Future Minimum Payments, Due in Two Years 2020 Operating Leases, Future Minimum Payments, Due in Three Years 2021 Operating Leases, Future Minimum Payments, Due in Four Years 2022 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total minimum future lease payments Operating Leases, Future Minimum Payments Due Other Commitments [Table] Other Commitments [Table] Other Commitments [Line Items] Other Commitments [Line Items] Loan facility Minimum purchase commitment Purchase Commitment, Remaining Minimum Amount Committed Purchase commitment, period Long-term Purchase Commitment, Period Balance Sheet Components Supplemental Balance Sheet Disclosures [Text Block] Goodwill and Intangible Assets Goodwill and Intangible Assets Disclosure [Text Block]