Align Technology (ALGN) 10-K 28 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document Documentand Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	ALGN
Entity Registrant Name	ALIGN TECHNOLOGY INC
Entity Central Index Key	1,097,149
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding (shares)		80,135,229
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 9,773,962,344
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net revenues	[1]	$ 1,473,413	$ 1,079,874	$ 845,486
Cost of net revenues		356,466	264,580	205,376
Gross profit		1,116,947	815,294	640,110
Operating expenses:
Selling, general and administrative		665,777	490,653	390,239
Research and development		97,559	75,720	61,237
Total operating expenses		763,336	566,373	451,476
Income from operations		353,611	248,921	188,634
Interest and other income (expense), net		11,188	(6,355)	(2,533)
Net income before provision for income taxes and equity in losses of investee		364,799	242,566	186,101
Provision for income taxes		130,162	51,200	42,081
Equity in losses of investee, net of tax		3,219	1,684	0
Net income		$ 231,418	$ 189,682	$ 144,020
Net income per share:
Basic (usd per share)		$ 2.89	$ 2.38	$ 1.80
Diluted (usd per share)		$ 2.83	$ 2.33	$ 1.77
Shares used in computing net income per share:
Basic (shares)		80,085	79,856	79,998
Diluted (shares)		81,832	81,484	81,521
[1]	Long-lived assets are attributed to countries based on entity that owns the assets.

CONSOLIDATED STATEMENT OF COMPR

CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 231,418	$ 189,682	$ 144,020
Net change in foreign currency translation adjustment	1,741	(670)	(154)
Change in unrealized gains (losses) on investments, net of tax	(232)	712	(686)
Other comprehensive income (loss)	1,509	42	(840)
Comprehensive income	$ 232,927	$ 189,724	$ 143,180

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 449,511	$ 389,275
Marketable securities, short-term	272,031	250,981
Accounts receivable, net of allowance for doubtful accounts and returns of $7,178 and $4,310, respectively	322,825	247,415
Inventories	31,688	27,131
Prepaid expenses and other current assets	80,948	38,176
Total current assets	1,157,003	952,978
Marketable securities, long-term	39,948	59,783
Property, plant and equipment, net	348,793	175,167
Equity method investments	54,606	45,061
Goodwill and intangible assets, net	89,068	81,998
Deferred tax assets	50,059	67,844
Other assets	38,379	13,320
Total assets	1,777,856	1,396,151
Current liabilities:
Accounts payable	36,776	28,596
Accrued liabilities	194,198	134,332
Deferred revenues	266,842	191,407
Total current liabilities	497,816	354,335
Income tax payable	114,091	45,133
Other long-term liabilities	15,579	1,294
Total liabilities	627,486	400,762
Commitments and contingencies (Notes 8 and 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value (5,000 shares authorized; none issued)	0	0
Common stock, $0.0001 par value (200,000 shares authorized; 80,040 and 79,553 issued and outstanding, respectively)	8	8
Additional paid-in capital	886,435	864,871
Accumulated other comprehensive income (loss), net	571	(938)
Retained earnings	263,356	131,448
Total stockholders’ equity	1,150,370	995,389
Total liabilities and stockholders’ equity	$ 1,777,856	$ 1,396,151

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts and returns	$ 7,178	$ 4,310
Preferred stock, par value (usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (shares)	5,000	5,000
Preferred stock, issued (shares)
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (shares)	200,000	200,000
Common stock, issued (shares)	80,040	79,553
Common stock, outstanding (shares)	80,040	79,553

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss), Net	Retained Earnings (Deficit)
Beginning Balance (in shares) at Dec. 31, 2014		80,205
Beginning Balance at Dec. 31, 2014	$ 752,771	$ 8	$ 783,410	$ (140)	$ (30,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	144,020				144,020
Net change in unrealized gains (losses) from investments	(686)			(686)
Net change in foreign currency translation adjustment	(164)		(10)	(154)
Issuance of common stock relating to employee equity compensation plans (in shares)		991
Issuance of common stock relating to employee equity compensation plans	11,325	$ 0	11,325
Tax withholdings related to net share settlements of restricted stock units	(20,716)		(20,716)
Common stock repurchased and retired (shares)		(1,696)
Common stock repurchased and retired	(101,791)		(15,669)		(86,122)
Net tax benefits from stock-based awards	10,224		10,224
Stock-based compensation	52,943		52,943
Ending Balance (in shares) at Dec. 31, 2015		79,500
Ending Balance at Dec. 31, 2015	847,926	$ 8	821,507	(980)	27,391
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	189,682				189,682
Net change in unrealized gains (losses) from investments	712			712
Net change in foreign currency translation adjustment	(670)		0	(670)
Issuance of common stock relating to employee equity compensation plans (in shares)		1,163
Issuance of common stock relating to employee equity compensation plans	13,778	$ 0	13,778
Tax withholdings related to net share settlements of restricted stock units	(29,857)		(29,857)
Common stock repurchased and retired (shares)		(1,110)
Common stock repurchased and retired	(96,218)		(10,593)		(85,625)
Net tax benefits from stock-based awards	15,888		15,888
Stock-based compensation	54,148		54,148
Ending Balance (in shares) at Dec. 31, 2016		79,553
Ending Balance at Dec. 31, 2016	995,389	$ 8	864,871	(938)	131,448
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	231,418
Net change in unrealized gains (losses) from investments	(232)			(232)
Net change in foreign currency translation adjustment	1,741			1,741
Issuance of common stock relating to employee equity compensation plans (in shares)		1,073
Issuance of common stock relating to employee equity compensation plans	14,461		14,461
Tax withholdings related to net share settlements of restricted stock units	(46,168)		(46,168)
Common stock repurchased and retired (shares)		(586)
Common stock repurchased and retired	(103,793)		(5,583)		(98,210)
Stock-based compensation	58,854		58,854
Ending Balance (in shares) at Dec. 31, 2017		80,040
Ending Balance at Dec. 31, 2017	1,150,370	$ 8	$ 886,435	$ 571	$ 263,356
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment from adoption of ASU 2016-16	$ (1,300)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 231,418	$ 189,682	$ 144,020
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred taxes	17,572	(16,401)	(11,424)
Depreciation and amortization	37,739	24,002	18,004
Stock-based compensation	58,854	54,148	52,943
Net tax benefits from stock-based awards	0	15,888	10,224
Excess tax benefit from share-based payment arrangements	0	(16,773)	(10,396)
Equity in losses of investee	3,219	1,684	0
Other non-cash operating activities	13,847	12,031	13,799
Changes in assets and liabilities, net of effects of acquisitions:
Accounts receivable	(90,990)	(94,444)	(40,775)
Inventories	(5,481)	(7,663)	(3,563)
Prepaid expenses and other assets	(8,669)	(9,390)	(3,726)
Accounts payable	8,175	(3,395)	7,575
Accrued and other long-term liabilities	24,235	30,007	12,532
Long-term income tax payable	68,958	7,622	6,930
Deferred revenues	79,662	60,656	41,854
Net cash provided by operating activities	438,539	247,654	237,997
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisition, net of cash acquired	(8,953)	0	0
Purchase of property, plant and equipment	(195,695)	(70,576)	(53,451)
Purchase of marketable securities	(390,244)	(405,612)	(447,092)
Proceeds from maturities of marketable securities	349,240	387,873	304,125
Purchase of equity method investments	(12,764)	(46,745)	0
Proceeds from sales of marketable securities	39,536	216,119	30,011
Loan advances to equity investee	(36,000)	0	0
Loan repayment from equity investee	6,000	0	0
Other investing activities	567	(8,211)	46
Net cash provided by (used in) investing activities	(248,313)	72,848	(166,361)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock	14,461	13,778	11,325
Common stock repurchases	(103,793)	(96,218)	(101,791)
Excess tax benefit from share-based payment arrangements	0	16,773	10,396
Employees’ taxes paid upon the vesting of restricted stock units	(46,168)	(29,857)	(20,716)
Net cash used in financing activities	(135,500)	(95,524)	(100,786)
Effect of foreign exchange rate changes on cash and cash equivalents	5,510	(3,417)	(3,007)
Net increase (decrease) in cash and cash equivalents	60,236	221,561	(32,157)
Cash and cash equivalents, beginning of year	389,275	167,714	199,871
Cash and cash equivalents, end of year	$ 449,511	$ 389,275	$ 167,714

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Business Description Align Technology, Inc. (“We”, “Our”, or “Align”) was incorporated in April 1997 in Delaware. Align is a global medical device company engaged in the design, manufacture and marketing of Invisalign® clear aligners and iTero® intraoral scanners and services for orthodontics and restorative and aesthetic dentistry. Align’s products are intended primarily for the treatment of malocclusion or the misalignment of teeth and are designed to help dental professionals achieve the clinical outcomes that they expect. We are headquartered in San Jose, California with offices worldwide. Our European headquarters is located in Amsterdam, the Netherlands and our Asia Pacific headquarters is located in Singapore. We have two operating segments: (1) Clear Aligner, known as the Invisalign System, and (2) Scanners and Services ("Scanner"), known as the iTero intraoral scanner and OrthoCAD services. Basis of Presentation and Preparation The consolidated financial statements include the accounts of Align and our wholly-owned subsidiaries after elimination of intercompany transactions and balances. In connection with the preparation of the consolidated financial statements, we evaluated events subsequent to the balance sheet date through the financial statement issuance date and determined that all material transactions have been recorded and disclosed properly. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles ("GAAP") in the United States of America (“U.S.”) requires our management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates. On an ongoing basis, we evaluate our estimates, including those related to the fair values of financial instruments, long-lived assets and goodwill, equity method investments, useful lives of intangible assets and property and equipment, revenue recognition, stock-based compensation, income taxes and contingent liabilities, among others. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Fair Value of Financial Instruments We measure our cash equivalents, marketable securities, Israeli fund and certain notes receivable at fair value. Fair value is the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 – Quoted (unadjusted) prices in active markets for identical assets or liabilities. Level 2 – Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability. Level 3 – Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability. Cash and Cash Equivalents We consider currency on hand, demand deposits, time deposits, and all highly liquid investments with an original or remaining maturity of three months or less at the date of purchase to be cash and cash equivalents. Cash and cash equivalents are held in various financial institutions in the U.S. and internationally. Restricted Cash Our restricted cash balance as of December 31, 2017 is not material. Our restricted cash balance as of December 31, 2016 was $3.7 million , of which $3.3 million was classified as a long-term asset and $0.4 million as a current asset. The restricted cash primarily consists of funds reserved for legal requirements. Marketable Securities We invest primarily in money market funds, commercial paper, corporate bonds, U.S. government agency bonds, asset-backed securities, municipal securities, U.S. government treasury bonds and certificates of deposits. Marketable securities are classified as available-for-sale and are carried at fair value. Marketable securities classified as current assets have maturities of less than one year. Unrealized gains or losses on such securities are included in accumulated other comprehensive income (loss), net in stockholders’ equity. Realized gains and losses from maturities of all such securities are reported in earnings and computed using the specific identification cost method. Realized gains or losses and charges for other-than-temporary declines in value, if any, on available-for-sale securities are reported in interest and other income (expense), net as incurred. We periodically evaluate these investments for other-than-temporary impairment. Variable Interest Entities We evaluate whether an entity in which we have made an investment is considered a variable interest entity (“VIE”). If we determine we are the primary beneficiary of a VIE, we would consolidate the VIE into our financial statements. In determining if we are the primary beneficiary, we evaluate whether we have the power to direct the activities that most significantly impact the VIE's economic performance and the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE. Our evaluation includes identification of significant activities and an assessment of our ability to direct those activities based on governance provisions and arrangements to provide or receive product and process technology, product supply, operations services, equity funding, financing, and other applicable agreements and circumstances. Our assessments of whether we are the primary beneficiary of a VIE require significant assumptions and judgments. We have concluded that we are not the primary beneficiary of our VIE investments; therefore, we do not consolidate their results into our consolidated financials. Investments in Privately Held Companies Investments in privately held companies in which we can exercise significant influence but do not own a majority equity interest or otherwise control, are accounted for under the equity method of accounting. Equity method investments are reported on our balance sheet as a single amount, and we record our share of their operating results within equity in losses of investee, net of tax, in our Consolidated Statement of Operations. Equity method investments are evaluated for impairment as events or circumstances indicate that there is an other-than-temporary loss in value. The decrease in value is recognized in the period the impairment occurs and recorded in interest and other income (expense), net in the Consolidated Statement of Operations. Derivative Financial Instruments We may enter into foreign currency forward contracts to minimize the short-term impact of foreign currency exchange rate fluctuations associated with certain assets and liabilities. These forward contracts are not designated as hedging instruments and do not subject us to material balance sheet risk due to fluctuations in foreign currency exchange rates. The gains and losses on these forward contracts are intended to offset the gains and losses in the underlying foreign currency denominated monetary assets and liabilities being economically hedged. We do not enter into foreign currency forward contracts for trading or speculative purposes. The net gain or loss from the settlement of these foreign currency forward contracts is recorded in interest and other income (expense), net in the Consolidated Statement of Operations. Foreign Currency For our international subsidiaries, we analyze on an annual basis or more often if necessary, if a significant change in facts and circumstances indicate that the functional currency has changed. For international subsidiaries where the local currency is the functional currency, adjustments from translating financial statements from the local currency to the U.S. dollar reporting currency are recorded as a separate component of accumulated other comprehensive income (loss), net in the stockholders’ equity section of the Consolidated Balance Sheet. This foreign currency translation adjustment reflects the translation of the balance sheet at period end exchange rates, and the income statement at an average exchange rate in effect during the period. The foreign currency revaluation that are derived from monetary assets and liabilities stated in a currency other than functional currency are included in interest and other income (expense), net. For the year ended December 31, 2017 , 2016 and 2015, we had foreign currency net gains (losses) of $9.0 million , $(8.0) million and $(4.0) million , respectively. Certain Risks and Uncertainties Our operating results depend to a significant extent on our ability to market and develop our products. The life cycles of our products are difficult to estimate due, in part, to the effect of future product enhancements and competition. Our inability to successfully develop and market our products as a result of competition or other factors would have a material adverse effect on our business, financial condition and results of operations. Our cash and investments are held primarily by three financial institutions. Financial instruments which potentially expose us to concentrations of credit risk consist primarily of cash equivalents and marketable securities. We invest excess cash primarily in money market funds, commercial paper, corporate bonds, U.S. government agency bonds, municipal securities, U.S. government treasury bonds, certificates of deposits and asset-backed securities. If the carrying value of our investments exceeds the fair value, and the decline in fair value is deemed to be other-than-temporary, we will be required to write down the value of our investments, which could adversely affect our results of operations and financial condition. Moreover, the performance of certain securities in our investment portfolio correlates with the credit condition of the U.S. economy. We provide credit to customers in the normal course of business. Collateral is not required for accounts receivable, but ongoing evaluations of customers’ credit worthiness are performed. We maintain reserves for potential credit losses and such losses have been within management’s expectations. No individual customer accounted for 10% or more of our accounts receivable at December 31, 2017 or 2016 , or net revenues for the year ended December 31, 2017 , 2016 or 2015 . In the U.S., the Food and Drug Administration (“FDA”) regulates the design, manufacture, distribution, pre-clinical and clinical study, clearance and approval of medical devices. Products developed by us may require approvals or clearances from the FDA or other international regulatory agencies prior to commercialized sales. There can be no assurance that our products will receive any of the required approvals or clearances. If we were denied approval or clearance or such approval was delayed, it may have a material adverse impact on us. We have manufacturing facilities located outside the U.S. In Juarez, Mexico, we manufacture our clear aligners, distribute and repair our scanners and perform our CAD/CAM services. In Or Yehuda, Israel, we produce our handheld intraoral scanner wand and perform the final assembly of our iTero scanner. Our digital treatment plans using a sophisticated, internally developed computer-modeling program are located in Costa Rica, China and Germany. Our reliance on international operations exposes us to related risks and uncertainties, including difficulties in staffing and managing international operations such as hiring and retaining qualified personnel; controlling production volume and quality of manufacture; political, social and economic instability, particularly as a result of increased levels of violence in Juarez, Mexico and Or Yehuda, Israel; interruptions and limitations in telecommunication services; product and material transportation delays or disruption; trade restrictions and changes in tariffs; import and export license requirements and restrictions; fluctuations in foreign currency exchange rates; and potential adverse tax consequences. If any of these risks materialize, our international manufacturing operations, as well as our operating results, may be harmed. We purchase certain inventory from sole suppliers. Additionally, we rely on a limited number of hardware manufacturers. The inability of any supplier or manufacturer to fulfill our supply requirements could materially and adversely impact our future operating results. Inventories Inventories are valued at the lower of cost or market, with cost computed using either standard cost, which approximates actual cost, or average cost on a first-in-first-out basis. Excess and obsolete inventories are determined primarily based on future demand forecasts, and write-downs of excess and obsolete inventories are recorded as a component of cost of net revenues. Property, Plant and Equipment Property, plant and equipment are stated at historical cost less accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets. Construction in progress ("CIP") is related to the construction or development of property (including land) and equipment that have not yet been placed in service for their intended use. Upon sale or retirement, the asset’s cost and related accumulated depreciation are removed from the balance sheet and any related gains or losses are reflected in operating expenses. Maintenance and repairs are expensed as incurred. Refer to Note 3 "Balance Sheet Components" of the Notes of Consolidated Financial Statements for details on estimated useful lives . Goodwill and Finite-Lived Acquired Intangible Assets Goodwill represents the excess of the purchase price paid over the fair value of tangible and identifiable intangible net assets acquired in business combinations and is allocated to the respective reporting units based on relative synergies generated. For the year ended December 31, 2017 and 2016, all goodwill is attributed to our Clear Aligner reporting unit. Our intangible assets primarily consist of intangible assets acquired as part of our acquisition of Cadent Holdings, Inc. on April 11, 2011. These assets are amortized using the straight-line method over their estimated useful lives ranging from one to fifteen years, reflecting the period in which the economic benefits of the assets are expected to be realized. Impairment of Goodwill and Long-Lived Assets Goodwill We evaluate goodwill for impairment at least annually on November 30th or more frequently if indicators are present, an event occurs or changes in circumstances suggest an impairment may exist and that it would more likely than not reduce the fair value of a reporting unit below its carrying amount. The allocation of goodwill to the respective reporting units is based on relative synergies generated as a result of an acquisition. We perform an initial assessment of qualitative factors to determine whether the existence of events and circumstances leads to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. In performing the qualitative assessment, we identify and consider the significance of relevant key factors, events, and circumstances that affect the fair value of our reporting units. These factors include external factors such as macroeconomic, industry, and market conditions, as well as entity-specific factors, such as our actual and planned financial performance. We also give consideration to the difference between the reporting unit fair value and carrying value as of the most recent date a fair value measurement was performed. If, after assessing the totality of relevant events and circumstances, we determine that it is more likely than not that the fair value of the reporting unit exceeds its carrying value and there is no indication of impairment, no further testing is performed; however, if we conclude otherwise, the first step of the two-step impairment test is performed by estimating the fair value of the reporting unit and comparing it with its carrying value, including goodwill. Step one of the goodwill impairment test consists of a comparison of the fair value of a reporting unit against its carrying amount, including the goodwill allocated to each reporting unit. We determine the fair value of our reporting units based on the present value of estimated future cash flows under the income approach of the reporting units as well as various price or market multiples applied to the reporting unit's operating results along with the appropriate control premium under the marketing approach, both of which are classified as level 3 within the fair value hierarchy as described in Note 2 "Marketable Securities and Fair Value Measurements" of the Notes of Consolidated Financial Statements . If the carrying amount of the reporting unit is in excess of its fair value, step two requires the comparison of the implied fair value of the reporting unit’s goodwill against the carrying amount of the reporting unit’s goodwill. Any excess of the carrying value of the reporting unit’s goodwill over the implied fair value of the reporting unit’s goodwill is recorded as an impairment loss in the Consolidated Statements of Operations. Finite-Lived Intangible Assets and Long-Lived Assets We evaluate long-lived assets (including finite-lived intangible assets) for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset group may not be recoverable. An asset or asset group is considered impaired if its carrying amount exceeds the future undiscounted net cash flows that the asset or asset group is expected to generate. Factors we consider important which could trigger an impairment review include significant negative industry or economic trends, significant loss of customers and changes in the competitive environment. If an asset or asset group is considered to be impaired, the impairment to be recognized is calculated as the amount by which the carrying amount of the asset or asset group exceeds its fair market value. Our estimates of future cash flows attributable to our long-lived assets require significant judgment based on our historical and anticipated results and are subject to many assumptions. The estimation of fair value utilizing a discounted cash flow approach includes numerous uncertainties which require our significant judgment when making assumptions of expected growth rates and the selection of discount rates, as well as assumptions regarding general economic and business conditions, and the structure that would yield the highest economic value, among other factors. Refer to Note 6 "Goodwill and Intangible Assets" of the Notes of Consolidated Financial Statements for details on intangible long-lived assets . There were no triggering events in 2017 that would cause an impairment of our goodwill or long-lived assets. Development Costs for Internal Use Software Internally developed software includes enterprise-level business software that we customize to meet our specific operational needs. Such capitalized costs include external direct costs utilized in developing or obtaining the applications and payroll and payroll-related costs for employees, who are directly associated with the development of the applications. Internally developed software costs capitalized during the year ended December 31, 2017 was not material. During the year ended December 31, 2016, we capitalized approximately $13.2 million related to our enterprise resource planning ("ERP") project which we placed into production during 2016 and amortize over its useful life of 10 years. The costs to develop software that is marketed externally have not been capitalized as we believe our current software development process is essentially completed concurrent with the establishment of technological feasibility. As such, all related software development costs are expensed as incurred and included in research and development expense in our Consolidated Statements of Operations. Product Warranty Clear Aligner We warrant our Invisalign products against material defects until the treatment plan is complete. We warrant SmileDirectClub, LLC (“SDC”) products against material defects for one year. We accrue for warranty costs in cost of net revenues upon shipment of products. The estimated warranty costs liability is primarily based on historical experience as to product failures as well as current information on replacement costs. Actual warranty costs could differ materially from the estimated amounts. We regularly review the warranty liability and update these balances based on historical warranty cost trends. Scanners and Services We warrant our intraoral scanners for a period of one year, which include materials and labor. We accrue for these warranty costs based on average historical repair costs. An extended warranty may be purchased for additional fees. Allowances for Doubtful Accounts and Sales Returns We maintain allowances for doubtful accounts for customers that are not able to make payments and allowances for sales returns. We periodically review these allowances, including an analysis of the customers’ payment history and information regarding the customers’ creditworthiness, as well as historical sales returns as a percentage of revenue. Actual write-offs have not materially differed from the estimated allowances. Revenue Recognition We measure and allocate revenue according to the accounting guidance for multiple-deliverable revenue arrangements in Accounting Standards Codification (“ASC”) 605-25, " Revenue Recognition – Multiple-Element Arrangements ." Multiple-Element Arrangements (“MEAs”): Arrangements with customers may include multiple deliverables, including any combination of products/equipment and services. The deliverables included in the MEAs are separated into more than one unit of accounting when (i) the delivered product/equipment has value to the customer on a stand-alone basis, and (ii) delivery of the undelivered service element(s) is probable and substantially in our control. Arrangement consideration is then allocated to each unit, delivered or undelivered, at the inception of the arrangement based on the relative selling price of each unit of accounting based first on vendor-specific objective evidence (“VSOE”) if it exists, second on third-party evidence (“TPE”) if it exists, or on best estimated selling price (“BESP”) if neither VSOE or TPE exist. • VSOE - In most instances, this applies to products and services that are sold separately in stand-alone arrangements. We determine VSOE based on pricing and discounting practices for the specific product or service when sold separately, considering geographical, customer, and other economic or marketing variables, as well as renewal rates or stand-alone prices for the service element(s). • TPE - If we cannot establish VSOE of selling price for a specific product or service included in a multiple-element arrangement, we use third-party evidence of selling price. We determine TPE based on sales of comparable amount of similar products or service offered by multiple third parties considering the degree of customization and similarity of product or service sold. • BESP - The best estimated selling price represents the price at which we would sell a product or service if it were sold on a stand-alone basis. When VSOE or TPE does not exist for all elements, we determine BESP for the arrangement element based on sales, cost and margin analysis, as well as other inputs based on our pricing practices. Adjustments for other market and company specific factors are made as deemed necessary in determining BESP. We regularly review our estimates of selling price and maintain internal controls over the establishment and update of these estimates. Revenue is recognized when persuasive evidence of the arrangement exists, the price is fixed or determinable, collectability is reasonably assured, title and risk of loss have passed to customers based on the shipping terms, and allowances for discounts, returns, and customer incentives can be reliably estimated. Provisions for discounts and rebates to customers are provided for in the same period that the related product sales are recorded. Clear Aligner We enter into arrangements (“treatment plan(s)”) that involve multiple future product deliverables. Invisalign Full, Invisalign Teen, and Invisalign Assist products include optional additional aligners at no charge for a period of up to five years after initial shipment and Invisalign Go includes optional additional aligners at no charge for a period of up to two years after initial shipment. Invisalign Teen also includes up to six optional replacement aligners in the price of the product and may be ordered by the dental professional any time throughout treatment. Invisalign Lite includes one optional case refinement in the price of the product. Case refinement is a finishing tool used to adjust a patient's teeth to the desired final position and may be elected by the dental professional at any time during treatment; however, it is generally ordered in the last stages of the treatment. We determined that our treatment plans, except Invisalign Assist with progress tracking, comprise the following deliverables which also represent separate units of accounting: initial aligners, additional aligners, case refinement, and replacement aligners. We allocate revenue for each treatment plan based on each unit's relative selling price based on BESP and recognize the revenue upon shipment of each unit in the treatment plan. For Invisalign Assist with the progress tracking feature, aligners and services are provided to the dental professional every nine stages (a "batch”). We are able to reliably estimate the number of batches which are expected to be shipped for each case based upon our historical experience. The amounts allocated to this deliverable are recognized on a prorated basis as each batch is shipped. Scanners and Services We recognize revenues from the sales of iTero intraoral scanners and CAD/CAM services. CAD/CAM services include scanning services, extended warranty for the intraoral scanners, a range of iTero restorative services, and OrthoCAD services such as OrthoCAD iRecord. We sell intraoral scanners and services through both our direct sales force and distribution partners. The intraoral scanner sales price includes one year of warranty, and, for additional fees, the customer may select an unlimited scanning service agreement over a fixed period of time or extended warranty periods. When intraoral scanners are sold with either an unlimited scanning service agreement and/or extended warranty, we allocate revenue based on each element's relative selling price. We estimate the selling price of each element, as if it is sold on a stand-alone basis, taking into consideration historical prices as well as our discounting strategies. Scanner revenue, net of related discounts and allowances, is recognized when products have been shipped and no significant obligations for installation or training remain. For certain distributors who provide installation and training to the customer, we recognize scanner revenue when the intraoral scanner is shipped to the distributor assuming all of the other revenue recognition criteria have been met. Discounts are deducted from revenue at the time of sale. Returns of products, excluding warranty related returns, are infrequent and insignificant. Service revenue, including iTero restorative and all OrthoCAD services are recognized upon delivery or ratably over the contract term as the specified services are performed. If a customer selects a pay per use basis for scanning service fees, the revenue is recognized as the service is provided. We offer customers an option to purchase extended warranties on certain products. We recognize revenue on these extended warranty contracts ratably over the life of the contract. The costs associated with these extended warranty contracts are recognized when incurred. Shipping and Handling Costs Shipping and handling charges to customers are included in net revenues, and the associated costs incurred are recorded in cost of net revenues. Legal Proceedings and Litigations We are involved in legal proceedings on an ongoing basis. If we believe that a loss arising from such matters is probable and can be reasonably estimated, we accrue the estimated loss in our consolidated financial statements. If only a range of estimated losses can be determined, we accrue an amount within the range that, in our judgment, reflects the most likely outcome; if none of the estimates within that range is a better estimate than any other amount, we accrue the low end of the range. Research and Development Research and development expense is expensed as incurred and includes the costs associated with the research and development of new products and enhancements to existing products. These costs primarily include personnel-related costs, including stock-based compensation, outside consulting expenses and allocations of corporate overhead expenses including facilities and IT. Advertising Costs The cost of advertising and media is expensed as incurred. For the year ended December 31, 2017 , 2016 and 2015 , we incurred advertising costs of $70.0 million , $36.0 million and $23.4 million , respectively. Common Stock Repurchase We repurchase our own common stock from time to time in the open market when our Board of Directors approve a stock repurchase program. We account for these repurchases under the accounting guidance for equity where we allocate the total repurchase value that is in excess over par value between additional paid-in capital and retained earnings. All shares repurchased are retired. Operating Leases We lease office spaces, vehicles and equipment under operating leases with original lease periods of up to 9 years. Certain of these leases have free or escalating rent payment provisions and lease incentives provided by the landlord. We recognize rent expense under such leases on a straight-line basis over the term of the lease. Income Taxes We make certain estimates and judgments in determining income tax expense for financial statement purposes. These estimates and judgments occur in the calculation of certain tax assets and liabilities, which arise from differences in the timing of recognition of revenue and expense for tax and financial statement purposes. As part of the process of preparing our consolidated financial statements, we are required to estimate our income taxes in each of the jurisdictions in which we operate. This process involves us estimating our current tax exposure under the applicable tax laws and assessing temporary differences resulting from differing treatment of items for tax and accounting purposes. These differences result in deferred tax assets and liabilities, which are included in our Consolidated Balance Sheet. We account for uncertainty in income taxes pursuant to authoritative guidance based on a two-step approach to recognize and measure uncertain tax positions taken or expected to be taken in a tax return. The first step is to determine if the weight of available evidence indicates that it is more likely than not that the tax position will be sustained on audit based on its technical merits, including resolution of any related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount that is more than 50% likely to be realized upon ultimate settlement. We adjust reserves for our uncertain tax positions due to changing facts and circumstances, such as the closing of a tax audit, or refinement of estimates due to new information. To the extent that the final outcome of these matters is different than the amounts recorded, such differences will

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Investments, All Other Investments [Abstract]
Marketable Securities and Fair Value Measurements	Marketable Securities and Fair Value Measurements As of December 31, 2017 and 2016 , the estimated fair value of our short-term and long-term marketable securities, classified as available for sale, is as follows (in thousands): Short-term December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 58,503 $ — $ (1 ) $ 58,502 Corporate bonds 145,728 3 (174 ) 145,557 U.S. government agency bonds 3,013 — (7 ) 3,006 U.S. government treasury bonds 60,650 — (70 ) 60,580 Certificates of deposit 4,386 — — 4,386 Total marketable securities, short-term $ 272,280 $ 3 $ (252 ) $ 272,031 Long-term December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. government agency bonds $ 15,023 $ — $ (68 ) $ 14,955 Corporate bonds 25,067 2 (76 ) 24,993 Total marketable securities, long-term $ 40,090 $ 2 $ (144 ) $ 39,948 Short-term December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 42,397 $ — $ (6 ) $ 42,391 Corporate bonds 122,788 22 (121 ) 122,689 Municipal securities 5,852 — (5 ) 5,847 U.S. government agency bonds 28,903 9 (4 ) 28,908 U.S. government treasury bonds 45,146 7 (7 ) 45,146 Certificates of deposit 6,000 — — 6,000 Total marketable securities, short-term $ 251,086 $ 38 $ (143 ) $ 250,981 Long-term December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. government agency bonds $ 6,805 $ — $ (16 ) $ 6,789 Corporate bonds 40,889 8 (85 ) 40,812 U.S. government treasury bonds 12,016 5 (16 ) 12,005 Asset-backed securities 177 — — 177 Total marketable securities, long-term $ 59,887 $ 13 $ (117 ) $ 59,783 Cash equivalents are not included in the tables above as the gross unrealized gains and losses are not material. We have no short-term or long-term investments that have been in a continuous material unrealized loss position for greater than twelve months as of December 31, 2017 and 2016. Amounts reclassified to earnings from accumulated other comprehensive income (loss), net related to unrealized gains or losses were not material in 2017 and 2016 . For the year ended December 31, 2017 and 2016 , realized gains or losses were not material. Our fixed-income securities investment portfolio consists of commercial paper, corporate bonds, municipal securities, U.S. government agency bonds, U.S. government treasury bonds, certificates of deposit and asset-backed securities that have a maximum effective maturity of 40 months on any individual security. The securities that we invest in are generally deemed to be low risk based on their credit ratings from the major rating agencies. The longer the duration of these securities, the more susceptible they are to changes in market interest rates and bond yields. As interest rates increase, those securities purchased at a lower yield show a mark-to-market unrealized loss. The unrealized losses are due primarily to changes in credit spreads and interest rates. We expect to realize the full value of all these investments upon maturity or sale. The weighted average remaining duration of these securities was approximately 6 months and 7 months as of December 31, 2017 and 2016, respectively. As the carrying value approximates the fair value for our short-term and long-term marketable securities shown in the tables above, the following table summarizes the fair value of our short-term and long-term marketable securities classified by maturity as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 One year or less $ 272,031 $ 250,981 Due in greater than one year 39,948 59,783 Total marketable securities $ 311,979 $ 310,764 Fair Value Measurements We measure the fair value of financial assets as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. We use the GAAP fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. This hierarchy requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The three levels of inputs that may be used to measure fair value: Level 1 — Quoted (unadjusted) prices in active markets for identical assets or liabilities. Our Level 1 assets consist of money market funds and U.S. government treasury bonds. We did not hold any Level 1 liabilities as of December 31, 2017 and 2016. Level 2 — Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability. Our Level 2 assets consist of commercial paper, corporate bonds, municipal securities, U.S. government agency and treasury bonds, certificates of deposit, asset-backed securities and our Israeli funds that are mainly invested in insurance policies. We obtain fair values for our Level 2 investments. Our custody bank and asset managers independently use professional pricing services to gather pricing data which may include quoted market prices for identical or comparable financial instruments, or inputs other than quoted prices that are observable either directly or indirectly, and we are ultimately responsible for these underlying estimates. We did not hold any Level 2 liabilities as of December 31, 2017 and 2016. Level 3 — Unobservable inputs to the valuation methodology that are supported by little or no market activity and that are significant to the measurement of the fair value of the assets or liabilities. Level 3 assets and liabilities include those whose fair value measurements are determined using pricing models, discounted cash flow methodologies or similar valuation techniques, as well as significant management judgment or estimation. Certain investments in private companies contain embedded derivatives, which do not require bifurcation as we elected to measure these investments at fair value. Our Level 3 assets consist of notes receivable due on December 31, 2018. We did not hold any Level 3 liabilities as of December 31, 2017 and 2016. The following table summarizes the reconciliation of assets measured and recorded at fair value on a recurring basis using significant unobservable inputs Level 3 (in thousands): Notes Receivable Balance as of December 31, 2016 (1) $ 2,047 Additional notes receivable issued 2,000 Accrued interest receivable 79 Change in fair value recognized in earnings 350 Balance as of December 31, 2017 (1) $ 4,476 (1) Balance was reclassified from Long-term notes receivable to Short-term notes receivable as of December 31, 2017 Refer to Note 9 "Commitments and Contingencies" of the Notes to Consolidated Financial Statements for more information on our investment with a privately held company. The following tables summarize our financial assets measured at fair value on a recurring basis as of December 31, 2017 and 2016 (in thousands): Description Balance as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Cash equivalents: Money market funds $ 253,155 $ 253,155 $ — $ — Commercial paper 7,246 — 7,246 — Corporate bonds 2,016 — 2,016 — Short-term investments: Commercial paper 58,502 — 58,502 — Corporate bonds 145,557 — 145,557 — U.S. government agency bonds 3,006 — 3,006 — U.S. government treasury bonds 60,580 60,580 — — Certificates of deposit 4,386 — 4,386 — Long-term investments: U.S. government agency bonds 14,955 — 14,955 — Corporate bonds 24,993 — 24,993 — Prepaid expenses and other current assets: Israeli funds 3,075 — 3,075 — Short-term notes receivable 4,476 — — 4,476 $ 581,947 $ 313,735 $ 263,736 $ 4,476 Description Balance as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Cash equivalents: Money market funds $ 87,179 $ 87,179 $ — $ — Commercial paper 2,499 — 2,499 — Corporate bonds 750 — 750 — Short-term investments: Commercial paper 42,391 — 42,391 — Corporate bonds 122,689 — 122,689 — Municipal securities 5,847 — 5,847 — U.S. government agency bonds 28,908 — 28,908 — U.S. government treasury bonds 45,146 45,146 — — Certificates of deposit 6,000 — 6,000 — Long-term investments: U.S. government agency bonds 6,789 — 6,789 — Corporate bonds 40,812 — 40,812 — U.S. government treasury bonds 12,005 12,005 — Asset-backed securities 177 — 177 — Prepaid expenses and other assets: Israeli funds 2,956 — 2,956 — Other assets: Long-term notes receivable 2,047 — — 2,047 $ 406,195 $ 144,330 $ 259,818 $ 2,047 Derivative Financial Instruments We have in the past and may in the future enter into foreign currency forward contracts to minimize the short-term impact of foreign currency exchange rate fluctuations associated with certain assets and liabilities. During 2017, we did not enter into foreign currency forward contracts. We had no foreign currency forward contracts outstanding as of December 31, 2016 and the net gain or loss on forward contracts was not material during the year ended December 31, 2016.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Balance Sheet Components Inventories Inventories consist of the following (in thousands): December 31, 2017 2016 Raw materials $ 12,721 $ 9,793 Work in process 12,157 10,773 Finished goods 6,810 6,565 Total inventories $ 31,688 $ 27,131 Property, Plant and Equipment, Net Property, plant and equipment consist of the following (in thousands): December 31, Generally Used Estimated Useful Life 2017 2016 Clinical and manufacturing equipment Up to 10 years $ 183,392 $ 153,938 Computer hardware 3 years 24,933 27,978 Computer software 3 years 54,756 59,997 Furniture and fixtures 5 years 16,271 10,306 Leasehold improvements Lease term (1) 37,756 22,370 Building 20 years 63,887 7,272 Land — 17,630 3,072 CIP — 85,976 25,948 Total 484,601 310,881 Less: Accumulated depreciation and amortization and impairment charges (135,808 ) (135,714 ) Total property, plant and equipment, net $ 348,793 $ 175,167 (1) Shorter of remaining lease term or estimated useful lives of asset Depreciation and amortization was $37.7 million , $24.0 million and $18.0 million , for the year ended December 31, 2017 , 2016 and 2015, respectively. Accrued Liabilities Accrued liabilities consist of the following (in thousands): December 31, 2017 2016 Accrued payroll and benefits $ 103,004 $ 79,214 Accrued expenses 27,318 21,811 Accrued income taxes 12,405 4,210 Accrued sales rebate 11,209 10,342 Accrued professional fees 6,316 3,604 Accrued warranty 5,929 3,841 Accrued sales tax and value added tax 5,503 5,032 Other accrued liabilities 22,514 6,278 Total accrued liabilities $ 194,198 $ 134,332 Warranty We regularly review the balance for accrued warranty and update based on historical warranty trends. Actual warranty costs incurred have not materially differed from those accrued; however, future actual warranty costs could differ from the estimated amounts. Accrued warranty as of December 31, 2017 and 2016 consists of the following activity (in thousands): Accrued warranty as of December 31, 2015 $ 2,638 Charged to cost of net revenues 4,894 Actual warranty expenditures (3,691 ) Accrued warranty as of December 31, 2016 3,841 Charged to cost of net revenues 7,195 Actual warranty expenditures (5,107 ) Accrued warranty as of December 31, 2017 $ 5,929

Equity Method Investments

Equity Method Investments	12 Months Ended
	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	Equity Method Investments On July 25, 2016, we acquired a 17% equity interest, on a fully diluted basis, in SmileDirectClub, LLC (“SDC”) for $46.7 million . The investment is accounted for under an equity method investment, and the investee, SDC, is considered a related party. The investment is reported in our Consolidated Balance Sheet under equity method investments, and we record our proportional share of SDC's income (losses) within equity in losses of investee, net of tax, in our Consolidated Statement of Operations. On July 24, 2017, we purchased an additional 2% equity interest in SDC for $12.8 million . As a result of this purchase, we hold a 19% equity interest in SDC on a fully diluted basis. As of December 31, 2017 and 2016, the balance of our equity method investments was $54.6 million and $45.1 million , respectively. Concurrently with the investment on July 25, 2016, we also entered into a supply agreement with SDC to manufacture clear aligners for SDC's doctor-led, at-home program for simple teeth straightening. The term of the supply agreement expires on December 31, 2019. We commenced supplying aligners to SDC in October 2016. The sale of aligners to SDC and the income from the supply agreement are reported in our Clear Aligner business segment after eliminating outstanding intercompany transactions. As of December 31, 2017 and 2016, the balance of accounts receivable due from SDC was $14.3 million and $0.1 million , respectively. For the year ended December 31, 2017 and 2016 , net revenues recognized from SDC were $24.1 million and $0.2 million , respectively. On July 25, 2016, we entered into a Loan and Security Agreement (the "Loan Agreement") with SDC and amended on July 24, 2017 where we agreed to provide SDC a loan of up to $30.0 million in one or more advances. As of December 31, 2017, $30.0 million of advances under the Loan Agreement were outstanding and no outstanding advances as of December 31, 2016. On February 7, 2018, $30.0 million of outstanding advances and related accrued interest were repaid in full, and the Loan Agreement was terminated ( Refer to Note 9 "Commitments and Contingencies" of the Notes to Consolidated Financial Statements for information on the Loan and Security Agreement with SDC). In February 2018, we received a communication on behalf of SDC Financial LLC, SmileDirectClub LLC, and the Members of SDC Financial LLC other than Align (collectively, the "SDC Entities") alleging that the launch and operation of our Invisalign store pilot program constitutes a breach of non-compete provisions applicable to the members of SDC Financial LLC, including Align. As a result of this alleged breach, SDC Financial LLC has notified Align that its members (other than Align) seek to exercise a right to repurchase all of Align’s SDC Financial LLC membership interests for a purchase price equal to the current capital account balance of Align. The SDC Entities also allege that Align has breached confidentiality provisions applicable to the SDC Financial LLC members and demands that Align cease all activities related to the Invisalign store pilot project, close existing Invisalign stores and cease using SDC’s confidential information. Align disputes the allegations that it has breached its obligations to the SDC Entities, including the allegation that the SDC Entities are entitled to exercise a repurchase right. Pursuant to the parties’ agreement, the dispute will be arbitrated if it is not resolved through negotiations. We are currently evaluating the potential impact that this could have on our consolidated financial statements.

Business Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Business Combinations	Business Combinations During the first quarter of 2017, we completed the acquisitions of certain distributors for the total estimated cash consideration of approximately $9.5 million including cash acquired. We preliminarily recorded $1.9 million of net tangible liabilities, $8.2 million of identifiable intangible assets and $3.2 million of goodwill. The preliminary fair values of net tangible liabilities and identifiable intangible assets acquired are based on preliminary valuations, and our estimates and assumptions are subject to change within the measurement period (up to one year from the acquisition date). The goodwill is primarily related to the benefit we expect to obtain from direct sales as we believe that the transition from our distributor arrangements to a direct sales model will increase our net revenues in the region as we will experience higher average sales prices (“ASP”) compared to our discounted ASP under the distribution agreements. The goodwill is not deductible for tax purposes. Pro forma results of operations for these acquisitions have not been presented as they are not material to our results of operations, either individually or in aggregate, for the period ended December 31, 2017.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill The change in the carrying value of goodwill for the year ended December 31, 2017 , all attributable to our Clear Aligner reporting unit, is as follows (in thousands): Total Balance as of December 31, 2015 $ 61,074 Adjustments (1) (30 ) Balance as of December 31, 2016 61,044 Goodwill from distributor acquisitions 3,247 Adjustments (1) 323 Balance as of December 31, 2017 $ 64,614 (1) The adjustments to goodwill during the period were related to foreign currency translation and/or purchase accounting adjustments within the measurement period. Impairment of Goodwill We evaluate goodwill for impairment at least annually on November 30th or more frequently if indicators are present, an event occurs or circumstances changes that suggest an impairment may exist and that it would more likely than not reduce the fair value of a reporting unit below its carrying amount. The allocation of goodwill to the respective reporting units is based on relative synergies generated as a result of an acquisition. Annual Impairment Test During the fourth quarter of fiscal 2017, we performed the annual goodwill impairment testing and found no impairment as the fair value of our Clear Aligner reporting unit was significantly in excess of its carrying value. Intangible Long-Lived Assets We amortize our intangible assets over their estimated useful lives. We evaluate long-lived assets, which includes property, plant and equipment and intangible assets, for impairment whenever events or changes in circumstances indicate the carrying value of an asset may not be recoverable. The carrying value is not recoverable if it exceeds the undiscounted cash flows resulting from the use of the asset and its eventual disposition. Our estimates of future cash flows attributable to our long-lived assets require significant judgment based on our historical and anticipated results and are subject to many factors. Factors we consider important which could trigger an impairment review include significant negative industry or economic trends, significant loss of customers and changes in the competitive environment of our intraoral scanning business. There were no triggering events in 2017 that would cause impairments of our long-lived assets. Acquired intangible long-lived assets are being amortized as follows (in thousands): Weighted Average Amortization Period (in years) Gross Carrying Amount as of December 31, 2017 Accumulated Amortization Accumulated Impairment Loss Net Carrying Value as of December 31, 2017 Trademarks 15 $ 7,100 $ (1,769 ) $ (4,179 ) $ 1,152 Existing technology 13 12,600 (4,704 ) (4,328 ) 3,568 Customer relationships 11 33,500 (14,681 ) (10,751 ) 8,068 Reacquired rights 1 3 7,500 (1,356 ) — 6,144 Patents 8 6,798 (1,504 ) — 5,294 Other 2 618 (390 ) — 228 Total intangible assets $ 68,116 $ (24,404 ) $ (19,258 ) $ 24,454 Weighted Average Amortization Period (in years) Gross Carrying Amount as of December 31, 2016 Accumulated Amortization Accumulated Impairment Loss Net Carrying Value as of December 31, 2016 Trademarks 15 $ 7,100 $ (1,631 ) $ (4,179 ) $ 1,290 Existing technology 13 12,600 (4,141 ) (4,328 ) 4,131 Customer relationships 11 33,500 (12,819 ) (10,751 ) 9,930 Patents 8 6,316 (713 ) — 5,603 Total intangible assets $ 59,516 $ (19,304 ) $ (19,258 ) $ 20,954 1 The fair value of reacquired rights obtained from distributor acquisitions during the first quarter of fiscal year 2017 is valued using the income approach. In addition, we effectively settled the pre-existing relationship with the distributors by assessing whether the distributor agreements include favorable or unfavorable terms compared to current market rates. Based on the assessment, we determined that the distributor agreements had terms that are consistent with market rates and, therefore, no settlement gains or losses are recorded associated with the acquisition. The total estimated future amortization expense for these acquired intangible assets as of December 31, 2017 is as follows (in thousands): Fiscal Year 2018 $ 6,379 2019 6,265 2020 3,869 2021 3,389 2022 2,116 Thereafter 2,436 Total $ 24,454

Credit Facility

Credit Facility	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Credit Facilities	Credit Facility We have a credit facility that provides for a $50.0 million revolving line of credit, with a $10.0 million letter of credit. The credit facility requires us to comply with specific financial conditions and performance requirements. On February 10, 2017, we amended the credit facility and extended the maturity date to March 22, 2018. The loans bear interest, at our option, at a fluctuating rate per annum equal to the daily one-month adjusted LIBOR rate plus a spread of 1.75% or an adjusted LIBOR rate (based on one, three, six or twelve-month interest periods) plus a spread of 1.75% . On July 24, 2017, we amended the credit facility's negative covenants to allow for a Costa Rica building purchase, an additional equity interest in SDC and an increase in SDC's loan limit. As of December 31, 2017, we had no outstanding borrowings under this credit facility and were in compliance with the conditions and performance requirements ( Refer to Note 4 "Equity Method Investments" of the Notes to Consolidated Financial Statements for information on the additional equity interest in SDC and Refer to Note 9 "Commitments and Contingencies" of the Notes to Consolidated Financial Statements for information on the Costa Rica building purchase and SDC loan agreement). On February 27, 2018, we entered into a new credit facility for a $200.0 million revolving line of credit, with a $50.0 million letter of credit, and a maturity date of February 27, 2021, replacing the existing credit facility. The credit facility requires us to comply with specific financial conditions and performance requirements. The loans bear interest, at our option, at either a rate based on the reserve adjusted LIBOR for the applicable interest period or a base rate, in each case plus a margin. The base rate is the highest of the credit facility’s publicly announced prime rate, the federal funds rate plus 0.50% and one month LIBOR plus 1.0% . The margin ranges from 1.25% to 1.75% for LIBOR loans and 0.25% to 0.75% for base rate loans. Interest on the loans is payable quarterly in arrears with respect to base rate loans and at the end of an interest period (and at three month intervals if the interest period exceeds three months) in the case of LIBOR loans. Principal, together with accrued and unpaid interest, is due on the maturity date.

Legal Proceedings

Legal Proceedings	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings	Legal Proceedings Securities Class Action Lawsuit On November 28, 2012, plaintiff City of Dearborn Heights Act 345 Police & Fire Retirement System filed a lawsuit against Align, Thomas M. Prescott (“Mr. Prescott”), Align’s former President and Chief Executive Officer, and Kenneth B. Arola (“Mr. Arola”), Align’s former Vice President, Finance and Chief Financial Officer, in the United States District Court for the Northern District of California on behalf of a purported class of purchasers of our common stock (the “Securities Action”). On July 11, 2013, an amended complaint was filed, which named the same defendants, on behalf of a purported class of purchasers of our common stock between January 31, 2012 and October 17, 2012. The amended complaint alleged that Align, Mr. Prescott and Mr. Arola violated Section 10(b) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder, and that Mr. Prescott and Mr. Arola violated Section 20(a) of the Securities Exchange Act of 1934. Specifically, the amended complaint alleged that during the purported class period defendants failed to take an appropriate goodwill impairment charge related to the April 29, 2011 acquisition of Cadent Holdings, Inc. in the fourth quarter of 2011, the first quarter of 2012 and the second quarter of 2012, which rendered our financial statements and projections of future earnings materially false and misleading and in violation of U.S. GAAP. The amended complaint sought monetary damages in an unspecified amount, costs and attorneys’ fees. On December 9, 2013, the court granted defendants’ motion to dismiss with leave for plaintiff to file a second amended complaint. Plaintiff filed a second amended complaint on January 8, 2014 on behalf of the same purported class. The second amended complaint states the same claims as the amended complaint. On August 22, 2014, the court granted our motion to dismiss without leave to amend. On September 22, 2014, Plaintiff filed a notice of appeal to the Ninth Circuit Court of Appeals. Briefing for the appeal was completed in May 2015 and the Ninth Circuit held oral arguments in October 2016. On May 5, 2017, the Ninth Circuit affirmed the district court's dismissal of the complaint. Plaintiff filed a request for rehearing that was denied by the Ninth Circuit on June 14, 2017. Plaintiff had 90 days following the June 14 Order to file a petition for a writ of certiorari with the United States Supreme Court which has passed and this case has been dismissed without leave to amend. Shareholder Derivative Lawsuit On February 1, 2013, plaintiff Gary Udis filed a shareholder derivative lawsuit against several of Align’s current and former officers and directors in the Superior Court of California, County of Santa Clara. The complaint alleges that our reported income and earnings were materially overstated because of a failure to timely write down goodwill related to the April 29, 2011 acquisition of Cadent Holdings, Inc., and that defendants made allegedly false statements concerning our forecasts. The complaint asserts various state law causes of action, including claims of breach of fiduciary duty, unjust enrichment, and insider trading, among others. The complaint seeks unspecified damages on behalf of Align, which is named solely as nominal defendant against whom no recovery is sought. The complaint also seeks an order directing Align to reform and improve its corporate governance and internal procedures, and seeks restitution in an unspecified amount, costs, and attorneys’ fees. On July 8, 2013, an Order was entered staying this derivative lawsuit until an initial ruling on our first motion to dismiss the Securities Action. On January 15, 2014, an Order was entered staying this derivative lawsuit until an initial ruling on our second motion to dismiss the Securities Action. On October 14, 2014, an Order was entered staying this derivative lawsuit until a ruling by the Ninth Circuit in the Securities Action discussed above. On June 28, 2017, the Court entered an Order dismissing this action with prejudice pursuant to a joint stipulation between the parties. Patent Infringement Lawsuit On November 14, 2017, Align filed six patent infringement lawsuits asserting 26 patents against 3Shape A/S, a Danish corporation, and a related U.S. corporate entity, asserting that 3Shape's Trios intraoral scanning system and Dental System software infringe Align patents. Align filed two Section 337 complaints with the U.S. International Trade Commission (ITC) alleging that 3Shape violates U.S. trade laws by selling for importation and importing its infringing Trios intraoral scanning system and Dental System software. Align's ITC complaints seek cease and desist orders and exclusion orders prohibiting the importation of 3Shape's Trios scanning system and Dental System software products into the U.S. Align also filed four separate complaints in the United States District Court for the District of Delaware alleging patent infringement by 3Shape's Trios intraoral scanning system and Dental System software. All of these district court complaints seek monetary damages and injunctive relief against further infringement. In addition, in the course of Align's operations, Align is involved in a variety of claims, suits, investigations, and proceedings, including actions with respect to intellectual property claims, patent infringement claims, government investigations, labor and employment claims, breach of contract claims, tax, and other matters. Regardless of the outcome, these proceedings can have an adverse impact on us because of defense costs, diversion of management resources, and other factors. Although the results of complex legal proceedings are difficult to predict and Align's view of these matters may change in the future as litigation and events related thereto unfold; Align currently does not believe that these matters, individually or in the aggregate, will materially affect Align's financial position, results of operations or cash flows.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Leases We lease our facilities and certain equipment and automobiles under non-cancelable operating lease arrangements that expire at various dates through 2027 and provide for pre-negotiated fixed rental rates during the terms of the lease. The terms of some of our leases provide for rental payments on a graduated scale. We recognize rent expense on a straight-line basis over the lease period. Total rent expense was $13.8 million , $9.9 million and $8.2 million , for the year ended December 31, 2017 , 2016 and 2015 , respectively. Sublease income is not material and excluded from the table below. Minimum future lease payments for non-cancelable leases as of December 31, 2017 , are as follows (in thousands): Fiscal Year Operating Leases 2018 $ 14,799 2019 13,260 2020 9,759 2021 8,137 2022 6,027 Thereafter 9,573 Total minimum lease payments $ 61,555 Other Commitments On July 25, 2016, we entered into a Loan and Security Agreement (the "Loan Agreement") with SmileDirectClub, LLC ("SDC") where we agreed to provide a loan of up to $15.0 million in one or more advances to SDC (the "Loan Facility"). On July 24, 2017, we amended the Loan Agreement with SDC to increase the line of credit up to $30.0 million . Available advances under the Loan Facility are subject to a borrowing base of 80% of SDC's eligible accounts receivable, determined in accordance with the terms of the Loan Agreement, and the satisfaction of other customary conditions. The advances bear interest, paid quarterly, at the rate of 7% per annum. Advances that are repaid or prepaid may be reborrowed. All outstanding principal and accrued and unpaid interest on the advances are due and payable on July 25, 2021. SDC's obligations in respect of the Loan Agreement are collateralized by a security interest in substantially all of SDC's assets. As of December 31, 2017 , $30.0 million of advances under the Loan Facility were outstanding. On February 7, 2018, $30.0 million of outstanding advances and related accrued interest were repaid in full and the Loan Agreement was terminated ( Refer to Note 4 "Equity Method Investments" of the Notes of Consolidated Financial Statements for more information on our investments in SDC). We have entered into certain investments with a privately held company where we have committed to purchase up to $5.0 million in convertible promissory notes. The first convertible promissory note was issued on July 14, 2016 for $2.0 million and a second convertible promissory note was issued on June 5, 2017 for $2.0 million . Both notes were outstanding as of December 31, 2017 . The remaining $1.0 million available is conditioned upon achievement of certain business milestones. The notes all mature on December 30, 2018 and accrue interest annually at 2.5% . On June 30, 2017, we entered into a non-cancelable Addendum to the Master Subscription Agreement with a software company to renew our software license subscription for the total price of $50.0 million over the next three years starting on January 1, 2018. On July 24, 2017, we entered into a Purchase and Sale Agreement to purchase a new Costa Rica treatment planning facility located in the Republic of Costa Rica for a purchase price of $26.1 million . As of December 31, 2017, we made payments of $20.9 million . On January 8, 2018, we paid the final payment of $5.2 million and closed the Purchase and Sale Agreement. On November 9, 2017, we entered into an Investment Agreement with the People’s Republic of China (“China Government”) where we have committed to invest a minimum of $46.0 million in Ziyang, China over five years to establish manufacturing operations. On November 15, 2017, we entered into another Purchase and Sale Agreement to purchase a building located in the Republic of Costa Rica for a purchase price of $25.6 million . The building will be used to support treatment planning and corporate administrative activities. As of December 31, 2017, we made payments of $6.8 million and the remaining payments are due in 2018. On November 27, 2017, we entered into a purchase agreement with one of our existing single source suppliers. Under the terms of the agreement, we are required to purchase a minimum approximately $305.2 million of aligner materials over the next 4 years. Off-Balance Sheet Arrangements As of December 31, 2017 , we had no material off-balance sheet arrangements that have, or are reasonably likely to have, a current or future material effect on our consolidated financial condition, results of operations, liquidity, capital expenditures or capital resources other than certain items disclosed in Other Commitments section above. Indemnification Provisions In the normal course of business to facilitate transactions in our services and products, we indemnify certain parties: customers, vendors, lessors, and other parties with respect to certain matters, including, but not limited to, services to be provided by us and intellectual property infringement claims made by third parties. In addition, we have entered into indemnification agreements with our directors and our executive officers that will require us, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. Several of these agreements limit the time within which an indemnification claim can be made and the amount of the claim. It is not possible to make a reasonable estimate of the maximum potential amount under these indemnification agreements due to the unique facts and circumstances involved in each particular agreement. Additionally, we have a limited history of prior indemnification claims and the payments we have made under such agreements have not had a material adverse effect on our results of operations, cash flows or financial position. However, to the extent that valid indemnification claims arise in the future, future payments by us could be significant and could have a material adverse effect on our results of operations or cash flows in a particular period. As of December 31, 2017 , we did not have any material indemnification claims that were probable or reasonably possible.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock The holders of common stock are entitled to receive dividends whenever funds are legally available and when and if declared by the Board of Directors. We have never declared or paid dividends on our common stock. Stock-Based Compensation Plans Our 2005 Incentive Plan, as amended, provides for the granting of incentive stock options, non-statutory stock options, restricted stock units, market stock units, stock appreciation rights, performance units and performance shares to employees, non-employee directors and consultants. Shares granted on or after May 16, 2013 as an award of restricted stock, restricted stock unit, market stock units, performance share or performance unit ("full value awards") are counted against the authorized share reserve as one and nine-tenths (1 9/10 ) shares for every one (1) share subject to the award, and any shares canceled that were counted as one and nine-tenths against the plan reserve will be returned at the same ratio. Full value awards granted prior to May 16, 2013 were counted against the authorized share reserve as one and one half (1 1/2 ) share for every one (1) share subject to the award, and any shares canceled that were counted as one and one half against the plan reserve will be returned at this same ratio. As of December 31, 2017 , the 2005 Incentive Plan (as amended) has a total reserve of 27,783,379 shares for issuance of which 6,885,248 shares are available for issuance. We issue new shares from our pool of authorized but unissued shares to satisfy the exercise and vesting obligations of our stock-based compensation plans. Stock-Based Compensation Stock-based compensation is based on the estimated fair value of awards, net of estimated forfeitures, and recognized over the requisite service period. Estimated forfeitures are based on historical experience at the time of grant and may be revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The stock-based compensation related to all of our stock-based awards and employee stock purchases for the year ended December 31, 2017 , 2016 and 2015 is as follows (in thousands): For the Year Ended December 31, 2017 2016 2015 Cost of net revenues $ 3,330 $ 3,966 $ 3,938 Selling, general and administrative 46,550 42,612 40,813 Research and development 8,974 7,570 8,192 Total stock-based compensation $ 58,854 $ 54,148 $ 52,943 Stock Options We have not granted options since 2011 and all outstanding options were fully vested and associated stock-based compensation was recognized as of December 31, 2015. Activity for the year ended December 31, 2017 , under the stock option plans is set forth below: Stock Options Number of Shares Underlying Stock Options (in thousands) Weighted Average Exercise Price per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 222 $ 14.90 Granted — — Exercised (143 ) 16.66 Cancelled or expired (4 ) 18.16 Outstanding as of December 31, 2017 75 $ 11.36 0.93 $ 15,752 Vested and expected to vest at December 31, 2017 75 $ 11.36 0.93 $ 15,752 Exercisable at December 31, 2017 75 $ 11.36 0.93 $ 15,752 The aggregate intrinsic value in the table above represents the total pre-tax intrinsic value (the difference between our closing stock price on the last trading day in 2017 and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had all option holders exercised their options on the last trading day of 2017. This amount will fluctuate based on the fair market value of our stock. The total intrinsic value of stock options exercised for the year ended December 31, 2017 , 2016 and 2015 was $ 18.1 million , $18.2 million and $7.4 million , respectively. The total fair value of the options vested during the year ended December 31, 2015 was not material. Restricted Stock Units The fair value of restricted stock units (“RSUs”) is based on our closing stock price on the date of grant. A summary for the year ended December 31, 2017 , is as follows: Shares Underlying RSUs (in thousands) Weighted Average Grant Date Fair Value Weighted Remaining Vesting Period (in years) Aggregate Intrinsic Value (in thousands) Nonvested as of December 31, 2016 1,789 $ 58.39 Granted 487 118.77 Vested and released (852 ) 54.24 Forfeited (83 ) 69.06 Nonvested as of December 31, 2017 1,341 $ 82.30 1.18 $ 297,973 The aggregate intrinsic value in the table above represents the total pre-tax intrinsic value (calculated by multiplying our closing stock price on the last trading day of 2017 by the number of nonvested RSUs) that would have been received by the unit holders had all RSUs been vested and released as of the last trading day of 2017. This amount will fluctuate based on the fair market value of our stock. During 2017 , of the 851,693 shares vested and released, 287,790 shares vested were withheld for employee minimum statutory tax obligations, resulting in a net issuance of 563,903 shares. The total intrinsic value of RSUs vested and released during 2017 , 2016 and 2015 was $99.5 million , $59.8 million and $45.9 million , respectively. The total fair value of RSUs vested during the year ended December 31, 2017 , 2016 and 2015 was $46.2 million , $39.1 million and $30.0 million , respectively. The weighted average grant date fair value of RSUs granted during 2017, 2016 and 2015 was $118.77 , $67.82 and $57.78 , respectively. As of December 31, 2017 , there was $72.9 million of total unamortized compensation costs, net of estimated forfeitures, related to RSUs and these costs are expected to be recognized over a weighted average period of 2.1 years. Market-Performance Based Restricted Stock Units On an annual basis, we grant market-performance based restricted stock units (“MSUs”) to our executive officers. Each MSU represents the right to one share of Align’s common stock and will be issued through our amended 2005 Incentive Plan. The actual number of MSUs which will be eligible to vest will be based on the performance of Align’s stock price relative to the performance of the NASDAQ Composite Index over the vesting period, generally two to three years , up to 200% of the MSUs initially granted. The following table summarizes the MSU performance as of December 31, 2017 : Number of Shares Underlying MSUs (in thousands) Weighted Average Grant Date Fair Value Weighted Average Remaining Vesting Period (in years) Aggregate Intrinsic Value (in thousands) Nonvested as of December 31, 2016 520 $ 60.49 Granted 201 88.80 Vested and released (283 ) 53.11 Forfeited (10 ) 64.50 Nonvested as of December 31, 2017 428 $ 78.53 0.97 $ 95,120 The aggregate intrinsic value in the table above represents the total pre-tax intrinsic value (calculated by multiplying our closing stock price on the last trading day of 2017 by the number of nonvested MSUs) that would have been received by the unit holders had all MSUs been vested and released as of the last trading day of 2017. This amount will fluctuate based on the fair market value of our stock. During 2017 , of the 282,548 shares vested and released 118,562 shares were withheld for tax payments, resulting in a net issuance of 163,986 shares. The total intrinsic value of MSUs vested and released during 2017 , 2016 and 2015 was $28.8 million , $17.4 million and $9.2 million , respectively. The total fair value of MSUs vested during the year ended December 31, 2017 , 2016 and 2015 was $15.0 million , $9.9 million and $4.9 million , respectively. As of December 31, 2017 , we expect to recognize $12.2 million of total unamortized compensation cost, net of estimated forfeitures, related to MSUs over a weighted average period of 1.0 years. The fair value of MSUs is estimated at the grant date using a Monte Carlo simulation that includes factors for market conditions. The following weighted-average assumptions used in the Monte Carlo simulation were as follows: Year Ended December 31, 2017 2016 2015 Expected term (in years) 3.0 3.0 3.0 Expected volatility 28.9 % 34.0 % 36.9 % Risk-free interest rate 1.5 % 0.9 % 1.0 % Expected dividends — — — Weighted average fair value per share at grant date $ 120.39 $ 68.88 $ 61.73 Total payments to tax authorities for payroll taxes related to RSUs, including MSUs, that vested during the period were $46.2 million , $29.9 million and $20.7 million during the year ended December 31, 2017 , 2016 and 2015 , respectively, and are reflected as a financing activity in the Consolidated Statement of Cash Flows. Employee Stock Purchase Plan In May 2010, our shareholders approved the 2010 Employee Stock Purchase Plan (the “2010 Purchase Plan”), which consists of consecutive overlapping twenty-four month offering periods with four six-month purchase periods in each offering period. Employees purchase shares at 85% of the lower of the fair market value of the common stock at either the beginning of the offering period or the end of the purchase period. The 2010 Purchase Plan will continue until terminated by either the Board of Directors or its administrator. The maximum number of shares available for issuance under the 2010 Purchase Plan is 2,400,000 shares. The following table summarizes the ESPP shares issued: Year Ended December 31, 2017 2016 2015 Number of shares issued (in thousands) 202 197 230 Weighted average price $ 59.93 $ 48.65 $ 36.66 As of December 31, 2017, 735,301 shares remain available for future issuance. The fair value of the option component of the 2010 Purchase Plan shares was estimated at the grant date using the Black-Scholes option pricing model with the following weighted average assumptions: Year Ended December 31, 2017 2016 2015 Expected term (in years) 1.2 1.2 1.2 Expected volatility 26.8 % 30.5 % 31.1 % Risk-free interest rate 1.0 % 0.7 % 0.3 % Expected dividends — — — Weighted average fair value at grant date $ 31.36 $ 22.23 $ 16.19 We recognized stock-based compensation expense related to our employee stock purchase plan of $5.4 million , $2.7 million and $4.1 million for the year ended December 31, 2017 , 2016 and 2015 , respectively. As of December 31, 2017 , there was $2.7 million of total unamortized compensation costs related to future employee stock purchases which we expect to be recognized over a weighted average period of 0.6 years.

Common Stock Repurchase Program

Common Stock Repurchase Program	12 Months Ended
	Dec. 31, 2017
Notes To Financial Statements [Abstract]
Share Repurchase Program Disclosure	Common Stock Repurchase Program April 2014 Repurchase Program On April 23, 2014, we announced that our Board of Directors had authorized a stock repurchase program ("April 2014 Repurchase Program") pursuant to which we may purchase up to $300.0 million of our common stock over a three year period. In 2015, we entered into an accelerated share purchase agreement ("2015 ASR") to repurchase $70.0 million of our common stock. The 2015 ASR was completed in July 2015. We received a total of approximately 1.2 million shares for an average share price of $60.52 . During 2015, we repurchased on the open market approximately 0.5 million shares of our common stock at an average price of $58.89 per share, including commissions, for an aggregate purchase price of approximately $31.8 million . In 2016, we entered into an accelerated share repurchase agreement ("2016 ASR") to repurchase $50.0 million of our common stock. The 2016 ASR was completed in September 2016. We received a total of approximately 0.6 million shares for an average share price of $81.89 . During 2016, we repurchased on the open market approximately 0.5 million shares of our common stock at an average price of $92.58 per share, including commissions, for an aggregate purchase price of approximately $46.2 million . In 2017, we repurchased on the open market approximately 0.04 million shares of our common stock at an average price of $96.37 per share, including commission for an aggregate purchase price of approximately $3.8 million , completing the April 2014 Repurchase Program. April 2016 Repurchase Program On April 28, 2016, we announced that our Board of Directors had authorized a plan to repurchase up to $300.0 million of the Company's stock ("April 2016 Repurchase Plan"). In 2016, we had no repurchases under this plan. In 2017, we entered into an accelerated share repurchase agreement ("2017 ASR") to repurchase $50.0 million of our common stock. The 2017 ASR was completed in August 2017. We received a total of approximately 0.4 million shares for an average share price of $146.48 . During 2017, we repurchased on the open market approximately 0.2 million shares of our common stock at an average price of $243.40 per share, including commissions, for an aggregate purchase price of approximately $50.0 million . As of December 31, 2017 , we have $200.0 million remaining under the April 2016 Repurchase Program. In February 2018, we repurchased on the open market approximately 0.4 million shares of our common stock at an average price of $252.24 per share, including commission for an aggregate purchase price of approximately $100.0 million .

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Compensation Related Costs [Abstract]
Employee Benefit Plans	Employee Benefit Plans 401(k) Plan We have defined contribution retirement plan under Section 401(k) of the Internal Revenue Code for our U.S. employees which covers substantially all U.S. employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. We match 50% of our employee’s salary deferral contributions up to a 6% of the employee’s eligible compensation effective 2010. We contributed approximately $4.3 million , $3.4 million and $2.7 million to the 401(k) plan during the year ended December 31, 2017 , 2016 and 2015 , respectively. Israeli Funds Under the Israeli severance fund law, we are required to make payments to dismissed employees and employees leaving employment in certain circumstances. The funding requirement is calculated based on the salary of the employee multiplied by the number of years of employment as of the applicable balance sheet date. Our Israeli employees are entitled to one month’s salary for each year of employment, or a pro-rata portion thereof. We fund the liability through monthly deposits into funds, and the values of these contributions are recorded in other current assets in the Consolidated Balance Sheet. As of December 31, 2017 and 2016 , the balance of the fund liability was approximately $3.2 million and $3.1 million , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The U.S. Tax Cuts and Jobs Act (the “TCJA”) was enacted into law on December 22, 2017, and impacted our effective tax rate for the year ended December 31, 2017. The TCJA made significant changes to the Internal Revenue Code, including, but not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017. We have estimated the impact of the TCJA and recorded $84.3 million of additional income tax expense in the fourth quarter of 2017, the period in which the legislation was enacted. The components of this expense are as follows: • We recorded a provisional tax amount of $73.9 million for the transition tax liability. We have not yet completed the calculation of the total post-1986 foreign Earnings and Profits ("E&P") and the income tax pools for all foreign subsidiaries. Further, the transition tax is based in part on the amount of those earnings held in cash and other specified assets. This amount may change when we finalize the calculation of post-1986 foreign E&P previously deferred from U.S. federal taxation and the amounts held in cash or other specified assets. In addition, further interpretations from U.S. federal and state governments and regulatory organizations may change the provisional liability or the accounting treatment of the provisional liability. • We recorded a provisional tax amount of $10.4 million to remeasure certain deferred tax assets and liabilities as a result of the enactment of the Act. We are still analyzing certain aspects of the TCJA and refining the estimate of the expected reversal of the deferred tax balances. The TCJA can potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts. The TCJA also includes provisions for certain foreign-sourced earnings referred to as Global Intangible Low-Taxed Income (“GILTI”), which impose a tax on foreign income in excess of a deemed return on tangible assets of foreign corporations. FASB guidance issued in January 2018 allows companies to make an accounting policy election to either (i) account for GILTI as a component of tax expense in the period in which the tax is incurred (the “period cost method”), or (ii) account for GILTI in the measurement of deferred taxes (the “deferred method”). Because of the complexity of the new provisions, we are continuing to evaluate the accounting impact under GAAP, and will make an election once this analysis has been completed. Net income before provision for income taxes and equity in losses of investee consists of the following (in thousands): Year ended December 31, 2017 2016 2015 Domestic $ 123,696 $ 118,871 $ 87,803 Foreign 241,103 123,695 98,298 Net income before provision for income taxes and equity in losses of investee $ 364,799 $ 242,566 $ 186,101 The provision for income taxes consists of the following (in thousands): Year Ended December 31, 2017 2016 2015 Federal Current $ 91,214 $ 40,235 $ 28,596 Deferred 15,724 24,794 6,679 106,938 65,029 35,275 State Current 2,580 2,603 3,271 Deferred 2,677 2,636 (703 ) 5,257 5,239 2,568 Foreign Current 15,285 8,964 4,305 Deferred 2,682 (28,032 ) (67 ) 17,967 (19,068 ) 4,238 Provision for income taxes $ 130,162 $ 51,200 $ 42,081 The differences between income taxes using the federal statutory income tax rate of 35% and our effective tax rate are as follows: Year Ended December 31, 2017 2016 2015 U.S. federal statutory income tax rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal tax benefit 1.4 2.1 1.5 Impact of U.S. Tax Cuts and Jobs Act 23.1 — — Impact of differences in foreign tax rates (18.0 ) (6.3 ) (16.2 ) Valuation allowance release for Israel — (12.9 ) — Stock-based compensation (6.3 ) 1.2 1.6 Other items not individually material 0.5 2.0 0.7 35.7 % 21.1 % 22.6 % As of December 31, 2017 , undistributed earnings of the company totaled $606.5 million . We reassessed our capital needs and investment strategy with regard to the indefinite reinvestment of the undistributed earnings from certain of our foreign subsidiaries as a result of the one-time transition tax on cumulative foreign earnings under the TCJA. During the fourth quarter of 2017, we determined that approximately $591.9 million of the total undistributed foreign earnings are no longer be considered to be indefinitely reinvested outside the U.S. As a result, we have recorded a deferred tax liability of approximately $3.3 million , which represents the provisional amount of U.S. state income taxes that would be due in the event these foreign earnings are distributed. The remaining amount of undistributed foreign earnings of approximately $14.7 million continues to be indefinitely reinvested in our international operations. Since U.S. federal income tax has already been provided under the provisions of the TCJA, the additional tax impact of the distribution of such foreign earnings to the United States parent would be limited to U.S. state income and withholding taxes and is not significant. On July 1, 2016, we implemented a new international corporate structure. This changed the structure of our international procurement and sales operations, as well as realigned the ownership and use of intellectual property among our wholly-owned subsidiaries. We continue to anticipate that an increasing percentage of our consolidated pre-tax income will be derived from, and reinvested in our foreign operations. We believe that income taxed in certain foreign jurisdictions at a lower rate relative to the U.S. federal statutory rate will have a beneficial impact on our worldwide effective tax rate over time. Although the license of intellectual property rights between consolidated entities did not result in any gain in the consolidated financial statements, the Company generated taxable income in certain jurisdictions in 2016 resulting in a tax expense of $34.3 million . Additionally, as a result of the restructuring, we reassessed the need for a valuation allowance against our deferred tax assets considering all available evidence. Given the current earnings and anticipated future earnings of our subsidiary in Israel, we concluded that we have sufficient positive evidence to release the valuation allowance against our Israel operating loss carryforwards of $31.4 million , which resulted in an income tax benefit in this period of the same amount. In June 2017, the Costa Rica Ministry of Foreign Trade, an agency of the Government of Costa Rica, granted an extension of certain income tax incentives for an additional twelve year period. Under these incentives, all of the income in Costa Rica is subject to a reduced tax rate. In order to receive the benefit of these incentives, we must hire a specified number of employees and maintain certain minimum levels of fixed asset investment in Costa Rica. If we do not fulfill these conditions for any reason, our incentive could lapse, and our income in Costa Rica would be subject to taxation at higher rates, which could have a negative impact on our operating results. The Costa Rica corporate income tax rate that would apply, absent the incentives, is 30% for 2017 , 2016 and 2015. As a result of these incentives, our income taxes were reduced by $1.8 million , $19.1 million and $32.7 million in the year ended December 31, 2017 , 2016 and 2015 , respectively, representing a benefit to diluted net income per share of $0.02 , $0.23 and $0.40 in the year ended December 31, 2017, 2016 and 2015, respectively. As of December 31, 2017 and 2016 , the significant components of our deferred tax assets and liabilities are (in thousands): Year Ended December 31, 2017 2016 Deferred tax assets: Net operating loss and capital loss carryforwards $ 24,971 $ 25,445 Reserves and accruals 12,547 22,954 Stock-based compensation 10,074 16,399 Deferred revenue 10,811 13,975 Net translation losses 1,928 1,634 Credit carryforwards 792 679 61,123 81,086 Deferred tax liabilities: Depreciation and amortization 7,522 12,034 Unremitted foreign earnings 3,305 — Prepaid expenses 751 969 11,578 13,003 Net deferred tax assets before valuation allowance 49,545 68,083 Valuation allowance (278 ) (256 ) Net deferred tax assets $ 49,267 $ 67,827 The total valuation allowance as of December 31, 2017 was not material. During the year ended December 31, 2017, the valuation allowance increased by a nominal amount which was mainly related to foreign currency translation adjustments. As of December 31, 2017, we have fully utilized California net operating loss carryforwards. As of December 31, 2017, we have California research credit carryforwards of approximately $4.1 million which can be carried forward indefinitely. In addition, we have foreign net operating loss carryforwards of approximately $104.7 million , the majority of which can be carried forward indefinitely, and a minor portion of which, if not utilized, will expire beginning in 2027. In the event of a change in ownership, as defined under federal and state tax laws, our tax credit carryforwards may be subject to annual limitations. The annual limitations may result in the expiration of the tax credit carryforwards before utilization. The changes in the balance of gross unrecognized tax benefits, which exclude interest and penalties, for the year ended December 31, 2017 , 2016 and 2015 , are as follows (in thousands): Unrecognized tax benefit as of December 31, 2014 $ 33,067 Tax positions related to current year: Additions for uncertain tax positions 6,346 Unrecognized tax benefit as of December 31, 2015 39,413 Tax positions related to current year: Additions for uncertain tax positions 6,971 Unrecognized tax benefit as of December 31, 2016 46,384 Tax positions related to current year: Additions for uncertain tax positions 1,819 Tax positions related to prior year: Additions for uncertain tax positions 1,809 Decreases for uncertain tax positions (826 ) Settlements with tax authorities (1,527 ) Reductions due to lapse of applicable statute of limitations (3 ) Unrecognized tax benefit as of December 31, 2017 $ 47,656 As of December 31, 2017 , $39.8 million of our unrecognized tax benefits would impact our effective tax rate if recognized. We have elected to recognize interest and penalties related to unrecognized tax benefits as a component of income taxes. For the year ended December 31, 2017 and 2016, interest and penalties included in tax expense was $0.8 million and $1.4 million , respectively. Our total interest and penalties accrued as of December 31, 2017 and 2016 was $2.9 million and $2.1 million , respectively. We do not expect any significant changes to the amount of unrecognized tax benefit within the next twelve months. We file U.S. federal, U.S. state, and non-U.S. income tax returns. Our major tax jurisdictions are U.S. federal and the state of California. For U.S. federal and state tax returns, we are no longer subject to tax examinations for years before 2000. With few exceptions, we are no longer subject to examination by foreign tax authorities for years before 2010.

Net Income per Share

Net Income per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Income per Share	Net Income per Share Basic net income per share is computed using the weighted average number of shares of common stock outstanding during the period. Diluted net income per share is computed using the weighted average number of shares of common stock, adjusted for any dilutive effect of potential common stock. Potential common stock, computed using the treasury stock method, includes RSUs, MSUs, stock options and our ESPP. The following table sets forth the computation of basic and diluted net income per share attributable to common stock (in thousands, except per share amounts): Year Ended December 31, 2017 2016 2015 Numerator: Net income $ 231,418 $ 189,682 $ 144,020 Denominator: Weighted-average common shares outstanding, basic 80,085 79,856 79,998 Dilutive effect of potential common stock 1,747 1,628 1,523 Total shares, diluted 81,832 81,484 81,521 Net income per share, basic $ 2.89 $ 2.38 $ 1.80 Net income per share, diluted $ 2.83 $ 2.33 $ 1.77 For the year ended December 31, 2017 , 2016 and 2015 , potentially anti-dilutive shares excluded from diluted net income per share related to RSUs, MSUs, stock options and ESPP were not material.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information The supplemental cash flow information consists of the following (in thousands): Year Ended December 31, 2017 2016 2015 Taxes paid $ 51,231 $ 47,289 $ 40,621 Non-cash investing activities: Fixed assets acquired with accounts payable or accrued liabilities $ 15,105 $ 4,434 $ 14,636 Fair value of option to purchase property $ 3,936 $ — $ —

Segments and Geographical Infor

Segments and Geographical Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segments and Geographical Information	Segments and Geographical Information Segment Information Operating segments are defined as components of an enterprise for which separate financial information is available that is evaluated regularly by the Chief Operating Decision Maker (“CODM”), or decision-making group, in deciding how to allocate resources and in assessing performance. Our CODM is our Chief Executive Officer. We report segment information based on the management approach. The management approach designates the internal reporting used by CODM for decision making and performance assessment as the basis for determining our reportable segments. The performance measures of our reportable segments include net revenues, gross profit and income from operations. Income from operations for each segment includes all geographic revenues, related cost of net revenues and operating expenses directly attributable to the segment. Certain operating expenses are attributable to operating segments and each allocation is measured differently based on the specific facts and circumstances of the costs being allocated. Costs not specifically allocated to segment income from operations include various corporate expenses such as stock-based compensation and costs related to IT, facilities, human resources, accounting and finance, legal and regulatory, and other separately managed general and administrative costs outside the operating segments. We group our operations into two reportable segments: Clear Aligner segment and Scanner segment. • Our Clear Aligner segment consists of Comprehensive Products, Non-Comprehensive Products and Non-Case revenues as defined below: • Comprehensive Products include our Invisalign Full, Teen and Assist products. • Non-Comprehensive Products include our Invisalign Express, Invisalign Lite, Invisalign i7 and Invisalign Go products in addition to revenues from the sale of aligners to SmileDirectClub (“SDC”) under our supply agreement. Revenue from SDC is recorded after eliminating outstanding intercompany transactions. • Non-Case includes our Vivera retainers along with our training and ancillary products for treating malocclusion. • Our Scanner segment consists of intraoral scanning systems and additional services available with the intraoral scanners that provide digital alternatives to the traditional cast models. This segment includes our iTero scanner and OrthoCAD services. These reportable operating segments are based on how our CODM views and evaluates our operations as well as allocation of resources. The following information relates to these segments (in thousands): For the Year Ended December 31, Net revenues 2017 2016 2015 Clear Aligner $ 1,309,262 $ 958,327 $ 800,186 Scanner 164,151 121,547 45,300 Total net revenues $ 1,473,413 $ 1,079,874 $ 845,486 Gross profit Clear Aligner $ 1,019,563 $ 747,494 $ 628,187 Scanner 97,384 67,800 11,923 Total gross profit $ 1,116,947 $ 815,294 $ 640,110 Income from operations Clear Aligner $ 564,648 $ 411,817 $ 371,113 Scanner 49,613 37,498 (12,337 ) Unallocated corporate expenses (260,650 ) (200,394 ) (170,142 ) Total income from operations $ 353,611 $ 248,921 $ 188,634 Depreciation and amortization Clear Aligner $ 21,581 $ 13,742 $ 9,842 Scanner 4,385 3,871 3,839 Unallocated corporate expenses 11,773 6,389 4,323 Total depreciation and amortization $ 37,739 $ 24,002 $ 18,004 The following table reconciles total segment income from operations in the table above to net income before provision for income taxes and equity losses of investee (in thousands): For the Year Ended December 31, 2017 2016 2015 Total segment income from operations $ 614,261 $ 449,315 $ 358,776 Unallocated corporate expenses (260,650 ) (200,394 ) (170,142 ) Total income from operations 353,611 248,921 188,634 Interest and other income (expense), net 11,188 (6,355 ) (2,533 ) Net income before provision for income taxes and equity losses of investee $ 364,799 $ 242,566 $ 186,101 Geographical Information Net revenues are presented below by geographic area (in thousands): For the Year Ended December 31, 2017 2016 2015 Net revenues (1) : United States (2) $ 836,200 $ 692,254 $ 585,874 The Netherlands (2) 456,108 286,911 167,128 Other International 181,105 100,709 92,484 Total net revenues $ 1,473,413 $ 1,079,874 $ 845,486 (1) Net revenues are attributed to countries based on location of where revenue is recognized. (2) Effective July 2016, we implemented a new international corporate structure. This changed the structure of our international procurement and sales operations. Tangible long-lived assets are presented below by geographic area (in thousands): As of December 31, 2017 2016 Long-lived assets (1) : The Netherlands $ 143,673 $ 104,039 United States 128,171 43,278 Costa Rica 30,738 2,657 Mexico 25,090 17,918 China 5,480 461 Other International 15,641 6,814 Total long-lived assets $ 348,793 $ 175,167 (1) Long-lived assets are attributed to countries based on entity that owns the assets.

Schedule II_ Valuation and Qual

Schedule II: Valuation and Qualifying Accounts and Reserves	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule II: Valuation and Qualifying Accounts and Reserves	SCHEDULE II: VALUATION AND QUALIFYING ACCOUNTS AND RESERVES Balance at Beginning of Period Additions (Reductions) to Costs and Expenses Write Offs Balance at End of Period (in thousands) Allowances for doubtful accounts and sales returns: Year ended December 31, 2015 $ 1,563 $ 8,944 $ (8,035 ) $ 2,472 Year ended December 31, 2016 $ 2,472 $ 8,585 $ (6,747 ) $ 4,310 Year ended December 31, 2017 $ 4,310 $ 9,948 $ (7,080 ) $ 7,178 Valuation allowance for deferred tax assets: Year ended December 31, 2015 $ 32,498 $ (813 ) $ — $ 31,685 Year ended December 31, 2016 $ 31,685 $ (31,429 ) $ — $ 256 Year ended December 31, 2017 $ 256 $ 21 $ — $ 277

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Business Description	Business Description Align Technology, Inc. (“We”, “Our”, or “Align”) was incorporated in April 1997 in Delaware. Align is a global medical device company engaged in the design, manufacture and marketing of Invisalign® clear aligners and iTero® intraoral scanners and services for orthodontics and restorative and aesthetic dentistry. Align’s products are intended primarily for the treatment of malocclusion or the misalignment of teeth and are designed to help dental professionals achieve the clinical outcomes that they expect. We are headquartered in San Jose, California with offices worldwide. Our European headquarters is located in Amsterdam, the Netherlands and our Asia Pacific headquarters is located in Singapore. We have two operating segments: (1) Clear Aligner, known as the Invisalign System, and (2) Scanners and Services ("Scanner"), known as the iTero intraoral scanner and OrthoCAD services.
Basis of Presentation and Preparation	Basis of Presentation and Preparation The consolidated financial statements include the accounts of Align and our wholly-owned subsidiaries after elimination of intercompany transactions and balances. In connection with the preparation of the consolidated financial statements, we evaluated events subsequent to the balance sheet date through the financial statement issuance date and determined that all material transactions have been recorded and disclosed properly.
Reclassification, Policy
Use of estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles ("GAAP") in the United States of America (“U.S.”) requires our management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates. On an ongoing basis, we evaluate our estimates, including those related to the fair values of financial instruments, long-lived assets and goodwill, equity method investments, useful lives of intangible assets and property and equipment, revenue recognition, stock-based compensation, income taxes and contingent liabilities, among others. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities.
Fair Value of Financial instruments	Fair Value of Financial Instruments We measure our cash equivalents, marketable securities, Israeli fund and certain notes receivable at fair value. Fair value is the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value is estimated by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 – Quoted (unadjusted) prices in active markets for identical assets or liabilities. Level 2 – Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability. Level 3 – Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider currency on hand, demand deposits, time deposits, and all highly liquid investments with an original or remaining maturity of three months or less at the date of purchase to be cash and cash equivalents. Cash and cash equivalents are held in various financial institutions in the U.S. and internationally.
Restricted Cash	Restricted Cash Our restricted cash balance as of December 31, 2017 is not material. Our restricted cash balance as of December 31, 2016 was $3.7 million , of which $3.3 million was classified as a long-term asset and $0.4 million as a current asset. The restricted cash primarily consists of funds reserved for legal requirements.
Marketable Securities	Marketable Securities We invest primarily in money market funds, commercial paper, corporate bonds, U.S. government agency bonds, asset-backed securities, municipal securities, U.S. government treasury bonds and certificates of deposits. Marketable securities are classified as available-for-sale and are carried at fair value. Marketable securities classified as current assets have maturities of less than one year. Unrealized gains or losses on such securities are included in accumulated other comprehensive income (loss), net in stockholders’ equity. Realized gains and losses from maturities of all such securities are reported in earnings and computed using the specific identification cost method. Realized gains or losses and charges for other-than-temporary declines in value, if any, on available-for-sale securities are reported in interest and other income (expense), net as incurred. We periodically evaluate these investments for other-than-temporary impairment.
Variable Interest Entities	Variable Interest Entities We evaluate whether an entity in which we have made an investment is considered a variable interest entity (“VIE”). If we determine we are the primary beneficiary of a VIE, we would consolidate the VIE into our financial statements. In determining if we are the primary beneficiary, we evaluate whether we have the power to direct the activities that most significantly impact the VIE's economic performance and the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE. Our evaluation includes identification of significant activities and an assessment of our ability to direct those activities based on governance provisions and arrangements to provide or receive product and process technology, product supply, operations services, equity funding, financing, and other applicable agreements and circumstances. Our assessments of whether we are the primary beneficiary of a VIE require significant assumptions and judgments. We have concluded that we are not the primary beneficiary of our VIE investments; therefore, we do not consolidate their results into our consolidated financials.
Investments in Privately Held Companies	Investments in Privately Held Companies Investments in privately held companies in which we can exercise significant influence but do not own a majority equity interest or otherwise control, are accounted for under the equity method of accounting. Equity method investments are reported on our balance sheet as a single amount, and we record our share of their operating results within equity in losses of investee, net of tax, in our Consolidated Statement of Operations. Equity method investments are evaluated for impairment as events or circumstances indicate that there is an other-than-temporary loss in value. The decrease in value is recognized in the period the impairment occurs and recorded in interest and other income (expense), net in the Consolidated Statement of Operations.
Derivative Financial Instruments	Derivative Financial Instruments We may enter into foreign currency forward contracts to minimize the short-term impact of foreign currency exchange rate fluctuations associated with certain assets and liabilities. These forward contracts are not designated as hedging instruments and do not subject us to material balance sheet risk due to fluctuations in foreign currency exchange rates. The gains and losses on these forward contracts are intended to offset the gains and losses in the underlying foreign currency denominated monetary assets and liabilities being economically hedged. We do not enter into foreign currency forward contracts for trading or speculative purposes. The net gain or loss from the settlement of these foreign currency forward contracts is recorded in interest and other income (expense), net in the Consolidated Statement of Operations.
Foreign Currency	Foreign Currency For our international subsidiaries, we analyze on an annual basis or more often if necessary, if a significant change in facts and circumstances indicate that the functional currency has changed. For international subsidiaries where the local currency is the functional currency, adjustments from translating financial statements from the local currency to the U.S. dollar reporting currency are recorded as a separate component of accumulated other comprehensive income (loss), net in the stockholders’ equity section of the Consolidated Balance Sheet. This foreign currency translation adjustment reflects the translation of the balance sheet at period end exchange rates, and the income statement at an average exchange rate in effect during the period. The foreign currency revaluation that are derived from monetary assets and liabilities stated in a currency other than functional currency are included in interest and other income (expense), net. For the year ended December 31, 2017 , 2016 and 2015, we had foreign currency net gains (losses) of $9.0 million , $(8.0) million and $(4.0) million , respectively.
Certain Risks and Uncertainties	Certain Risks and Uncertainties Our operating results depend to a significant extent on our ability to market and develop our products. The life cycles of our products are difficult to estimate due, in part, to the effect of future product enhancements and competition. Our inability to successfully develop and market our products as a result of competition or other factors would have a material adverse effect on our business, financial condition and results of operations. Our cash and investments are held primarily by three financial institutions. Financial instruments which potentially expose us to concentrations of credit risk consist primarily of cash equivalents and marketable securities. We invest excess cash primarily in money market funds, commercial paper, corporate bonds, U.S. government agency bonds, municipal securities, U.S. government treasury bonds, certificates of deposits and asset-backed securities. If the carrying value of our investments exceeds the fair value, and the decline in fair value is deemed to be other-than-temporary, we will be required to write down the value of our investments, which could adversely affect our results of operations and financial condition. Moreover, the performance of certain securities in our investment portfolio correlates with the credit condition of the U.S. economy. We provide credit to customers in the normal course of business. Collateral is not required for accounts receivable, but ongoing evaluations of customers’ credit worthiness are performed. We maintain reserves for potential credit losses and such losses have been within management’s expectations. No individual customer accounted for 10% or more of our accounts receivable at December 31, 2017 or 2016 , or net revenues for the year ended December 31, 2017 , 2016 or 2015 . In the U.S., the Food and Drug Administration (“FDA”) regulates the design, manufacture, distribution, pre-clinical and clinical study, clearance and approval of medical devices. Products developed by us may require approvals or clearances from the FDA or other international regulatory agencies prior to commercialized sales. There can be no assurance that our products will receive any of the required approvals or clearances. If we were denied approval or clearance or such approval was delayed, it may have a material adverse impact on us. We have manufacturing facilities located outside the U.S. In Juarez, Mexico, we manufacture our clear aligners, distribute and repair our scanners and perform our CAD/CAM services. In Or Yehuda, Israel, we produce our handheld intraoral scanner wand and perform the final assembly of our iTero scanner. Our digital treatment plans using a sophisticated, internally developed computer-modeling program are located in Costa Rica, China and Germany. Our reliance on international operations exposes us to related risks and uncertainties, including difficulties in staffing and managing international operations such as hiring and retaining qualified personnel; controlling production volume and quality of manufacture; political, social and economic instability, particularly as a result of increased levels of violence in Juarez, Mexico and Or Yehuda, Israel; interruptions and limitations in telecommunication services; product and material transportation delays or disruption; trade restrictions and changes in tariffs; import and export license requirements and restrictions; fluctuations in foreign currency exchange rates; and potential adverse tax consequences. If any of these risks materialize, our international manufacturing operations, as well as our operating results, may be harmed. We purchase certain inventory from sole suppliers. Additionally, we rely on a limited number of hardware manufacturers. The inability of any supplier or manufacturer to fulfill our supply requirements could materially and adversely impact our future operating results.
Inventories	Inventories Inventories are valued at the lower of cost or market, with cost computed using either standard cost, which approximates actual cost, or average cost on a first-in-first-out basis. Excess and obsolete inventories are determined primarily based on future demand forecasts, and write-downs of excess and obsolete inventories are recorded as a component of cost of net revenues.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are stated at historical cost less accumulated depreciation and amortization. Depreciation and amortization are computed using the straight-line method over the estimated useful lives of the assets. Construction in progress ("CIP") is related to the construction or development of property (including land) and equipment that have not yet been placed in service for their intended use. Upon sale or retirement, the asset’s cost and related accumulated depreciation are removed from the balance sheet and any related gains or losses are reflected in operating expenses. Maintenance and repairs are expensed as incurred. Refer to Note 3 "Balance Sheet Components" of the Notes of Consolidated Financial Statements for details on estimated useful lives .
Goodwill and Finite-Lived Acquired Intangible Assets	Goodwill and Finite-Lived Acquired Intangible Assets Goodwill represents the excess of the purchase price paid over the fair value of tangible and identifiable intangible net assets acquired in business combinations and is allocated to the respective reporting units based on relative synergies generated. For the year ended December 31, 2017 and 2016, all goodwill is attributed to our Clear Aligner reporting unit. Our intangible assets primarily consist of intangible assets acquired as part of our acquisition of Cadent Holdings, Inc. on April 11, 2011. These assets are amortized using the straight-line method over their estimated useful lives ranging from one to fifteen years, reflecting the period in which the economic benefits of the assets are expected to be realized.
Impairment of Goodwill and Long-Lived Assets	Impairment of Goodwill and Long-Lived Assets Goodwill We evaluate goodwill for impairment at least annually on November 30th or more frequently if indicators are present, an event occurs or changes in circumstances suggest an impairment may exist and that it would more likely than not reduce the fair value of a reporting unit below its carrying amount. The allocation of goodwill to the respective reporting units is based on relative synergies generated as a result of an acquisition. We perform an initial assessment of qualitative factors to determine whether the existence of events and circumstances leads to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. In performing the qualitative assessment, we identify and consider the significance of relevant key factors, events, and circumstances that affect the fair value of our reporting units. These factors include external factors such as macroeconomic, industry, and market conditions, as well as entity-specific factors, such as our actual and planned financial performance. We also give consideration to the difference between the reporting unit fair value and carrying value as of the most recent date a fair value measurement was performed. If, after assessing the totality of relevant events and circumstances, we determine that it is more likely than not that the fair value of the reporting unit exceeds its carrying value and there is no indication of impairment, no further testing is performed; however, if we conclude otherwise, the first step of the two-step impairment test is performed by estimating the fair value of the reporting unit and comparing it with its carrying value, including goodwill. Step one of the goodwill impairment test consists of a comparison of the fair value of a reporting unit against its carrying amount, including the goodwill allocated to each reporting unit. We determine the fair value of our reporting units based on the present value of estimated future cash flows under the income approach of the reporting units as well as various price or market multiples applied to the reporting unit's operating results along with the appropriate control premium under the marketing approach, both of which are classified as level 3 within the fair value hierarchy as described in Note 2 "Marketable Securities and Fair Value Measurements" of the Notes of Consolidated Financial Statements . If the carrying amount of the reporting unit is in excess of its fair value, step two requires the comparison of the implied fair value of the reporting unit’s goodwill against the carrying amount of the reporting unit’s goodwill. Any excess of the carrying value of the reporting unit’s goodwill over the implied fair value of the reporting unit’s goodwill is recorded as an impairment loss in the Consolidated Statements of Operations. Finite-Lived Intangible Assets and Long-Lived Assets We evaluate long-lived assets (including finite-lived intangible assets) for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset group may not be recoverable. An asset or asset group is considered impaired if its carrying amount exceeds the future undiscounted net cash flows that the asset or asset group is expected to generate. Factors we consider important which could trigger an impairment review include significant negative industry or economic trends, significant loss of customers and changes in the competitive environment. If an asset or asset group is considered to be impaired, the impairment to be recognized is calculated as the amount by which the carrying amount of the asset or asset group exceeds its fair market value. Our estimates of future cash flows attributable to our long-lived assets require significant judgment based on our historical and anticipated results and are subject to many assumptions. The estimation of fair value utilizing a discounted cash flow approach includes numerous uncertainties which require our significant judgment when making assumptions of expected growth rates and the selection of discount rates, as well as assumptions regarding general economic and business conditions, and the structure that would yield the highest economic value, among other factors. Refer to Note 6 "Goodwill and Intangible Assets" of the Notes of Consolidated Financial Statements for details on intangible long-lived assets . There were no triggering events in 2017 that would cause an impairment of our goodwill or long-lived assets.
Development Costs for Internal Use Software	Development Costs for Internal Use Software Internally developed software includes enterprise-level business software that we customize to meet our specific operational needs. Such capitalized costs include external direct costs utilized in developing or obtaining the applications and payroll and payroll-related costs for employees, who are directly associated with the development of the applications. Internally developed software costs capitalized during the year ended December 31, 2017 was not material. During the year ended December 31, 2016, we capitalized approximately $13.2 million related to our enterprise resource planning ("ERP") project which we placed into production during 2016 and amortize over its useful life of 10 years. The costs to develop software that is marketed externally have not been capitalized as we believe our current software development process is essentially completed concurrent with the establishment of technological feasibility. As such, all related software development costs are expensed as incurred and included in research and development expense in our Consolidated Statements of Operations.
Product Warranty	Product Warranty Clear Aligner We warrant our Invisalign products against material defects until the treatment plan is complete. We warrant SmileDirectClub, LLC (“SDC”) products against material defects for one year. We accrue for warranty costs in cost of net revenues upon shipment of products. The estimated warranty costs liability is primarily based on historical experience as to product failures as well as current information on replacement costs. Actual warranty costs could differ materially from the estimated amounts. We regularly review the warranty liability and update these balances based on historical warranty cost trends. Scanners and Services We warrant our intraoral scanners for a period of one year, which include materials and labor. We accrue for these warranty costs based on average historical repair costs. An extended warranty may be purchased for additional fees.
Allowance for Doubtful Accounts and Sales Returns	Allowances for Doubtful Accounts and Sales Returns We maintain allowances for doubtful accounts for customers that are not able to make payments and allowances for sales returns. We periodically review these allowances, including an analysis of the customers’ payment history and information regarding the customers’ creditworthiness, as well as historical sales returns as a percentage of revenue. Actual write-offs have not materially differed from the estimated allowances.
Revenue Recognition	Revenue Recognition We measure and allocate revenue according to the accounting guidance for multiple-deliverable revenue arrangements in Accounting Standards Codification (“ASC”) 605-25, " Revenue Recognition – Multiple-Element Arrangements ." Multiple-Element Arrangements (“MEAs”): Arrangements with customers may include multiple deliverables, including any combination of products/equipment and services. The deliverables included in the MEAs are separated into more than one unit of accounting when (i) the delivered product/equipment has value to the customer on a stand-alone basis, and (ii) delivery of the undelivered service element(s) is probable and substantially in our control. Arrangement consideration is then allocated to each unit, delivered or undelivered, at the inception of the arrangement based on the relative selling price of each unit of accounting based first on vendor-specific objective evidence (“VSOE”) if it exists, second on third-party evidence (“TPE”) if it exists, or on best estimated selling price (“BESP”) if neither VSOE or TPE exist. • VSOE - In most instances, this applies to products and services that are sold separately in stand-alone arrangements. We determine VSOE based on pricing and discounting practices for the specific product or service when sold separately, considering geographical, customer, and other economic or marketing variables, as well as renewal rates or stand-alone prices for the service element(s). • TPE - If we cannot establish VSOE of selling price for a specific product or service included in a multiple-element arrangement, we use third-party evidence of selling price. We determine TPE based on sales of comparable amount of similar products or service offered by multiple third parties considering the degree of customization and similarity of product or service sold. • BESP - The best estimated selling price represents the price at which we would sell a product or service if it were sold on a stand-alone basis. When VSOE or TPE does not exist for all elements, we determine BESP for the arrangement element based on sales, cost and margin analysis, as well as other inputs based on our pricing practices. Adjustments for other market and company specific factors are made as deemed necessary in determining BESP. We regularly review our estimates of selling price and maintain internal controls over the establishment and update of these estimates. Revenue is recognized when persuasive evidence of the arrangement exists, the price is fixed or determinable, collectability is reasonably assured, title and risk of loss have passed to customers based on the shipping terms, and allowances for discounts, returns, and customer incentives can be reliably estimated. Provisions for discounts and rebates to customers are provided for in the same period that the related product sales are recorded. Clear Aligner We enter into arrangements (“treatment plan(s)”) that involve multiple future product deliverables. Invisalign Full, Invisalign Teen, and Invisalign Assist products include optional additional aligners at no charge for a period of up to five years after initial shipment and Invisalign Go includes optional additional aligners at no charge for a period of up to two years after initial shipment. Invisalign Teen also includes up to six optional replacement aligners in the price of the product and may be ordered by the dental professional any time throughout treatment. Invisalign Lite includes one optional case refinement in the price of the product. Case refinement is a finishing tool used to adjust a patient's teeth to the desired final position and may be elected by the dental professional at any time during treatment; however, it is generally ordered in the last stages of the treatment. We determined that our treatment plans, except Invisalign Assist with progress tracking, comprise the following deliverables which also represent separate units of accounting: initial aligners, additional aligners, case refinement, and replacement aligners. We allocate revenue for each treatment plan based on each unit's relative selling price based on BESP and recognize the revenue upon shipment of each unit in the treatment plan. For Invisalign Assist with the progress tracking feature, aligners and services are provided to the dental professional every nine stages (a "batch”). We are able to reliably estimate the number of batches which are expected to be shipped for each case based upon our historical experience. The amounts allocated to this deliverable are recognized on a prorated basis as each batch is shipped. Scanners and Services We recognize revenues from the sales of iTero intraoral scanners and CAD/CAM services. CAD/CAM services include scanning services, extended warranty for the intraoral scanners, a range of iTero restorative services, and OrthoCAD services such as OrthoCAD iRecord. We sell intraoral scanners and services through both our direct sales force and distribution partners. The intraoral scanner sales price includes one year of warranty, and, for additional fees, the customer may select an unlimited scanning service agreement over a fixed period of time or extended warranty periods. When intraoral scanners are sold with either an unlimited scanning service agreement and/or extended warranty, we allocate revenue based on each element's relative selling price. We estimate the selling price of each element, as if it is sold on a stand-alone basis, taking into consideration historical prices as well as our discounting strategies. Scanner revenue, net of related discounts and allowances, is recognized when products have been shipped and no significant obligations for installation or training remain. For certain distributors who provide installation and training to the customer, we recognize scanner revenue when the intraoral scanner is shipped to the distributor assuming all of the other revenue recognition criteria have been met. Discounts are deducted from revenue at the time of sale. Returns of products, excluding warranty related returns, are infrequent and insignificant. Service revenue, including iTero restorative and all OrthoCAD services are recognized upon delivery or ratably over the contract term as the specified services are performed. If a customer selects a pay per use basis for scanning service fees, the revenue is recognized as the service is provided. We offer customers an option to purchase extended warranties on certain products. We recognize revenue on these extended warranty contracts ratably over the life of the contract. The costs associated with these extended warranty contracts are recognized when incurred.
Shipping and Handling Costs	Shipping and Handling Costs Shipping and handling charges to customers are included in net revenues, and the associated costs incurred are recorded in cost of net revenues.
Legal Proceedings and Litigations	Legal Proceedings and Litigations We are involved in legal proceedings on an ongoing basis. If we believe that a loss arising from such matters is probable and can be reasonably estimated, we accrue the estimated loss in our consolidated financial statements. If only a range of estimated losses can be determined, we accrue an amount within the range that, in our judgment, reflects the most likely outcome; if none of the estimates within that range is a better estimate than any other amount, we accrue the low end of the range.
Research and Development	Research and Development Research and development expense is expensed as incurred and includes the costs associated with the research and development of new products and enhancements to existing products. These costs primarily include personnel-related costs, including stock-based compensation, outside consulting expenses and allocations of corporate overhead expenses including facilities and IT.
Advertising Costs	Advertising Costs The cost of advertising and media is expensed as incurred. For the year ended December 31, 2017 , 2016 and 2015 , we incurred advertising costs of $70.0 million , $36.0 million and $23.4 million , respectively.
Common Stock Repurchase	Common Stock Repurchase We repurchase our own common stock from time to time in the open market when our Board of Directors approve a stock repurchase program. We account for these repurchases under the accounting guidance for equity where we allocate the total repurchase value that is in excess over par value between additional paid-in capital and retained earnings. All shares repurchased are retired.
Operating Leases	Operating Leases We lease office spaces, vehicles and equipment under operating leases with original lease periods of up to 9 years. Certain of these leases have free or escalating rent payment provisions and lease incentives provided by the landlord. We recognize rent expense under such leases on a straight-line basis over the term of the lease.
Income Taxes	Income Taxes We make certain estimates and judgments in determining income tax expense for financial statement purposes. These estimates and judgments occur in the calculation of certain tax assets and liabilities, which arise from differences in the timing of recognition of revenue and expense for tax and financial statement purposes. As part of the process of preparing our consolidated financial statements, we are required to estimate our income taxes in each of the jurisdictions in which we operate. This process involves us estimating our current tax exposure under the applicable tax laws and assessing temporary differences resulting from differing treatment of items for tax and accounting purposes. These differences result in deferred tax assets and liabilities, which are included in our Consolidated Balance Sheet. We account for uncertainty in income taxes pursuant to authoritative guidance based on a two-step approach to recognize and measure uncertain tax positions taken or expected to be taken in a tax return. The first step is to determine if the weight of available evidence indicates that it is more likely than not that the tax position will be sustained on audit based on its technical merits, including resolution of any related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount that is more than 50% likely to be realized upon ultimate settlement. We adjust reserves for our uncertain tax positions due to changing facts and circumstances, such as the closing of a tax audit, or refinement of estimates due to new information. To the extent that the final outcome of these matters is different than the amounts recorded, such differences will impact our tax provision in our Consolidated Statement of Operation in the period in which such determination is made. We assess the likelihood that we will be able to realize our deferred tax assets. Should there be a change in our ability to realize our deferred tax assets, our tax provision would increase in the period in which we determine that it is more likely than not that we cannot realize our deferred tax assets. We consider all available evidence, both positive and negative, including historical levels of income, expectations and risks associated with estimates of future taxable income and ongoing prudent and feasible tax planning strategies in assessing the need for a valuation allowance. If it is more likely than not that we will not realize our deferred tax assets, we will increase our provision for taxes by recording a valuation allowance against the deferred tax assets that we estimate will not ultimately be realizable. The available positive evidence at December 31, 2017 included historical operating profits and a projection of future income sufficient to realize most of our remaining deferred tax assets. As of December 31, 2017 , it was considered more likely than not that our deferred tax assets would be realized with the exception of certain foreign loss carryovers as we are unable to forecast sufficient future profits to realize the deferred tax assets. The U.S. Tax Cuts and Jobs Act (the “TCJA”) was enacted into law on December 22, 2017 and impacted our effective tax rate for the year ended December 31, 2017. The TCJA made significant changes to the Internal Revenue Code, including, but not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings as of December 31, 2017.
Stock-based compensation	Stock-Based Compensation We recognize stock-based compensation cost for shares expected to vest on a straight-line basis over the requisite service period of the award, net of estimated forfeitures. We use the Black-Scholes option pricing model to determine the fair value of employee stock purchase plan shares. We estimate the fair value of market-performance based restricted stock units using a Monte Carlo simulation model which requires the input of assumptions, including expected term, stock price volatility and the risk-free rate of return. In addition, judgment is also required in estimating the number of stock-based awards that are expected to be forfeited. Forfeitures are estimated based on historical experience at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The assumptions used in calculating the fair value of share-based payment awards represent management’s best estimates, but these estimates involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and we use different assumptions, our stock-based compensation expense could be materially different in the future.
Comprehensive Income	Comprehensive Income Comprehensive income includes all changes in equity during a period from non-owner sources. Comprehensive income, including unrealized gains and losses on investments and foreign currency translation adjustments, are reported net of their related tax effect.
Recent Accounting Pronouncements	Recent Accounting Pronouncements (i) New Accounting Updates Recently Adopted In January 2017, the Financial Accounting Standards Board ("FASB") issued ASU 2017-01, “ Business Combinations (Topic 805): Clarifying the Definition of a Business, ” to clarify the definition of a business when evaluating whether transactions should be accounted for as acquisitions of assets or businesses. We early adopted the standard in the fourth quarter of fiscal year 2017 on a prospective basis and our adoption did not have a material impact on our consolidated financial statements and related disclosures. In March 2016, the FASB issued Accounting Standards Update ("ASU") 2016-09, " Improvements to Employee Share-Based Payment Accounting " (Topic 718) . We adopted the standard in the first quarter of fiscal year 2017. With this adoption, excess tax benefits related to stock-based compensation expense are reflected in our consolidated statement of operations as a component of the provision for income taxes instead of additional paid-in capital in our consolidated balance sheet. In addition, we elected to continue to estimate expected forfeitures rather than as they occur to determine the amount of compensation cost to be recognized in each period. During the fiscal year ended December 31, 2017, we recognized excess tax benefits of $30.0 million in our provision for income taxes. Excess tax benefits from share-based payment arrangements are classified as an operating activity in our consolidated statement of cash flows. In October 2016, the FASB issued ASU 2016-16, "Intra-Entity Transfers of Assets Other Than Inventory," (Topic 740) which requires entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. We early adopted the standard in the first quarter of fiscal year 2017 by applying the modified retrospective approach and recognized a $1.3 million decrease to retained earnings as a cumulative-effect adjustment. (ii) Recent Accounting Updates Not Yet Effective In May 2014, the FASB released ASU 2014-9, " Revenue from Contracts with Customers, " (Topic 606) to supersede nearly all existing revenue recognition guidance under GAAP. The core principle of the standard is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for the goods or services. The new standard defines a five step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than required under existing GAAP including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. In addition, the new standard requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. We plan to adopt the standard in the first quarter of fiscal year 2018 by applying the full retrospective method. Prior periods will be retrospectively adjusted and we will recognize the cumulative effect of adopting this guidance as an adjustment to our opening balance of retained earnings as of January 1, 2016. We have assessed the financial statement impact of adoption including, but not limited to, volume-based discount programs, sales commissions and the identification of performance obligations, and are continuing to evaluate the transition and disclosure requirements of the standard. We anticipate the adoption of Topic 606 will not have a material impact to our consolidated financial statements. In April 2016, the FASB released ASU 2016-10, " Revenue from Contracts with Customers, " to clarify the following two aspects of Topic 606: identifying performance obligations and the licensing implementation guidance, while retaining the principles for those areas of the ASU 2014-9 issued in May 2014. The effective date and the transition requirement of the amendments in this update are the same as the effective date and transition requirements of Topic 606. In May 2016, the FASB released ASU 2016-12, " Revenue from Contracts with Customers, " to address certain issues in the Topic 606 guidance on assessing the collectability, presentation of sales taxes, non-cash consideration, and completed contracts and contract modifications at transition. The ASU provides narrow-scope improvements and practical expedients to the ASU 2014-9 issued in May 2014. The effective date and the transition requirement of the amendments in this update are the same as the effective date and transition requirements of Topic 606. In December 2016, the FASB released ASU 2016-20, " Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, " to clarify certain aspects of guidance in the Topic 606 including its scope, disclosure requirements and contract cost accounting, while retaining the principles for those areas of the ASU 2014-9 issued in May 2014. The effective date and the transition requirement of the amendments in this update are the same as the effective date and transition requirements of Topic 606. In February 2016, the FASB issued ASU 2016-02, “ Leases ” (Topic 842) to increase transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The updated guidance is effective for annual periods beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption of the standard is permitted. We plan to adopt the standard in the first quarter of fiscal year 2019 by electing practical expedients available in the standard. While we are currently evaluating the impact of the adoption of this guidance on our consolidated financial statements, we expect the adoption will have a material increase to the assets and liabilities of our consolidated balance sheet. In June 2016, the FASB issued ASU 2016-13, “ Financial Instruments - Credit Losses ” (Topic 326) . The FASB issued this update to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The amendments in this update replace the existing guidance of incurred loss impairment methodology with an approach that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The updated guidance is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption of the update is permitted in fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. We are currently evaluating the impact of this guidance on our consolidated financial statements and related disclosures. In August 2016, the FASB issued ASU 2016-15, "Classification of Certain Cash Receipts and Cash Payments" (Topic 230). This FASB clarifies the presentation and classification of certain cash receipts and cash payments in the statements of cash flows. The amendments are effective for fiscal years and interim periods within those years beginning after December 15, 2017. We plan to adopt the guidance in the first quarter of fiscal year 2018 and we do not expect that the guidance will have a material impact on our consolidated statements of cash flows. In November 2016, the FASB issued ASU 2016-18, "Statement of Cash Flows - Restricted Cash," which provides guidance to address the classification and presentation of changes in restricted cash in the statements of cash flows . The amendments are effective for fiscal years and interim periods within those years beginning after December 15, 2017 on a retrospective basis. We plan to adopt the guidance in the first quarter of fiscal year 2018 and we do not expect that the guidance will have a material impact on our consolidated statements of cash flows. In January 2017, the FASB issued ASU 2017-04, “Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment," to simplify the subsequent measurement of goodwill by eliminating step two from the goodwill impairment test. Under the amendments, an entity will recognize an impairment charge for the amount by which the carrying value exceeds the fair value. The amendments are effective for fiscal years and interim periods within those years beginning after December 15, 2019 on a prospective basis, and early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements and related disclosures. In May 2017, the FASB issued ASU 2017-09, " Compensation — Stock Compensation (Topic 718): Scope of Modification Accounting," to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. The amendments are effective for fiscal years and interim periods within those years beginning after December 15, 2017 on a prospective basis. We are plan to adopt the guidance in the first quarter of fiscal year 2018 and we do not expect that the guidance will have a material impact on our consolidated financial statements and related disclosures.
Net Income per Share	Basic net income per share is computed using the weighted average number of shares of common stock outstanding during the period. Diluted net income per share is computed using the weighted average number of shares of common stock, adjusted for any dilutive effect of potential common stock. Potential common stock, computed using the treasury stock method, includes RSUs, MSUs, stock options and our ESPP.

Marketable Securities and Fai26

Marketable Securities and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, All Other Investments [Abstract]
Short-Term And Long-Term Marketable Securities	As of December 31, 2017 and 2016 , the estimated fair value of our short-term and long-term marketable securities, classified as available for sale, is as follows (in thousands): Short-term December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 58,503 $ — $ (1 ) $ 58,502 Corporate bonds 145,728 3 (174 ) 145,557 U.S. government agency bonds 3,013 — (7 ) 3,006 U.S. government treasury bonds 60,650 — (70 ) 60,580 Certificates of deposit 4,386 — — 4,386 Total marketable securities, short-term $ 272,280 $ 3 $ (252 ) $ 272,031 Long-term December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. government agency bonds $ 15,023 $ — $ (68 ) $ 14,955 Corporate bonds 25,067 2 (76 ) 24,993 Total marketable securities, long-term $ 40,090 $ 2 $ (144 ) $ 39,948 Short-term December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 42,397 $ — $ (6 ) $ 42,391 Corporate bonds 122,788 22 (121 ) 122,689 Municipal securities 5,852 — (5 ) 5,847 U.S. government agency bonds 28,903 9 (4 ) 28,908 U.S. government treasury bonds 45,146 7 (7 ) 45,146 Certificates of deposit 6,000 — — 6,000 Total marketable securities, short-term $ 251,086 $ 38 $ (143 ) $ 250,981 Long-term December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. government agency bonds $ 6,805 $ — $ (16 ) $ 6,789 Corporate bonds 40,889 8 (85 ) 40,812 U.S. government treasury bonds 12,016 5 (16 ) 12,005 Asset-backed securities 177 — — 177 Total marketable securities, long-term $ 59,887 $ 13 $ (117 ) $ 59,783
Marketable Securities	As the carrying value approximates the fair value for our short-term and long-term marketable securities shown in the tables above, the following table summarizes the fair value of our short-term and long-term marketable securities classified by maturity as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 One year or less $ 272,031 $ 250,981 Due in greater than one year 39,948 59,783 Total marketable securities $ 311,979 $ 310,764
Fair value, Assets measured on a recurring basis, unobservable input reconciliation	The following table summarizes the reconciliation of assets measured and recorded at fair value on a recurring basis using significant unobservable inputs Level 3 (in thousands): Notes Receivable Balance as of December 31, 2016 (1) $ 2,047 Additional notes receivable issued 2,000 Accrued interest receivable 79 Change in fair value recognized in earnings 350 Balance as of December 31, 2017 (1) $ 4,476 (1) Balance was reclassified from Long-term notes receivable to Short-term notes receivable as of December 31, 2017
Financial Assets Measured At Fair Value On A Recurring Basis	The following tables summarize our financial assets measured at fair value on a recurring basis as of December 31, 2017 and 2016 (in thousands): Description Balance as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Cash equivalents: Money market funds $ 253,155 $ 253,155 $ — $ — Commercial paper 7,246 — 7,246 — Corporate bonds 2,016 — 2,016 — Short-term investments: Commercial paper 58,502 — 58,502 — Corporate bonds 145,557 — 145,557 — U.S. government agency bonds 3,006 — 3,006 — U.S. government treasury bonds 60,580 60,580 — — Certificates of deposit 4,386 — 4,386 — Long-term investments: U.S. government agency bonds 14,955 — 14,955 — Corporate bonds 24,993 — 24,993 — Prepaid expenses and other current assets: Israeli funds 3,075 — 3,075 — Short-term notes receivable 4,476 — — 4,476 $ 581,947 $ 313,735 $ 263,736 $ 4,476 Description Balance as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Cash equivalents: Money market funds $ 87,179 $ 87,179 $ — $ — Commercial paper 2,499 — 2,499 — Corporate bonds 750 — 750 — Short-term investments: Commercial paper 42,391 — 42,391 — Corporate bonds 122,689 — 122,689 — Municipal securities 5,847 — 5,847 — U.S. government agency bonds 28,908 — 28,908 — U.S. government treasury bonds 45,146 45,146 — — Certificates of deposit 6,000 — 6,000 — Long-term investments: U.S. government agency bonds 6,789 — 6,789 — Corporate bonds 40,812 — 40,812 — U.S. government treasury bonds 12,005 12,005 — Asset-backed securities 177 — 177 — Prepaid expenses and other assets: Israeli funds 2,956 — 2,956 — Other assets: Long-term notes receivable 2,047 — — 2,047 $ 406,195 $ 144,330 $ 259,818 $ 2,047

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Schedule of Inventories	Inventories consist of the following (in thousands): December 31, 2017 2016 Raw materials $ 12,721 $ 9,793 Work in process 12,157 10,773 Finished goods 6,810 6,565 Total inventories $ 31,688 $ 27,131
Property, Plant and Equipment	Property, plant and equipment consist of the following (in thousands): December 31, Generally Used Estimated Useful Life 2017 2016 Clinical and manufacturing equipment Up to 10 years $ 183,392 $ 153,938 Computer hardware 3 years 24,933 27,978 Computer software 3 years 54,756 59,997 Furniture and fixtures 5 years 16,271 10,306 Leasehold improvements Lease term (1) 37,756 22,370 Building 20 years 63,887 7,272 Land — 17,630 3,072 CIP — 85,976 25,948 Total 484,601 310,881 Less: Accumulated depreciation and amortization and impairment charges (135,808 ) (135,714 ) Total property, plant and equipment, net $ 348,793 $ 175,167 (1) Shorter of remaining lease term or estimated useful lives of asset
Schedule of Accrued Liabilities	Accrued liabilities consist of the following (in thousands): December 31, 2017 2016 Accrued payroll and benefits $ 103,004 $ 79,214 Accrued expenses 27,318 21,811 Accrued income taxes 12,405 4,210 Accrued sales rebate 11,209 10,342 Accrued professional fees 6,316 3,604 Accrued warranty 5,929 3,841 Accrued sales tax and value added tax 5,503 5,032 Other accrued liabilities 22,514 6,278 Total accrued liabilities $ 194,198 $ 134,332
Warranty accrual	Accrued warranty as of December 31, 2017 and 2016 consists of the following activity (in thousands): Accrued warranty as of December 31, 2015 $ 2,638 Charged to cost of net revenues 4,894 Actual warranty expenditures (3,691 ) Accrued warranty as of December 31, 2016 3,841 Charged to cost of net revenues 7,195 Actual warranty expenditures (5,107 ) Accrued warranty as of December 31, 2017 $ 5,929

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The change in the carrying value of goodwill for the year ended December 31, 2017 , all attributable to our Clear Aligner reporting unit, is as follows (in thousands): Total Balance as of December 31, 2015 $ 61,074 Adjustments (1) (30 ) Balance as of December 31, 2016 61,044 Goodwill from distributor acquisitions 3,247 Adjustments (1) 323 Balance as of December 31, 2017 $ 64,614 (1) The adjustments to goodwill during the period were related to foreign currency translation and/or purchase accounting adjustments within the measurement period.
Schedule of Amortized Intangible Assets	Acquired intangible long-lived assets are being amortized as follows (in thousands): Weighted Average Amortization Period (in years) Gross Carrying Amount as of December 31, 2017 Accumulated Amortization Accumulated Impairment Loss Net Carrying Value as of December 31, 2017 Trademarks 15 $ 7,100 $ (1,769 ) $ (4,179 ) $ 1,152 Existing technology 13 12,600 (4,704 ) (4,328 ) 3,568 Customer relationships 11 33,500 (14,681 ) (10,751 ) 8,068 Reacquired rights 1 3 7,500 (1,356 ) — 6,144 Patents 8 6,798 (1,504 ) — 5,294 Other 2 618 (390 ) — 228 Total intangible assets $ 68,116 $ (24,404 ) $ (19,258 ) $ 24,454 Weighted Average Amortization Period (in years) Gross Carrying Amount as of December 31, 2016 Accumulated Amortization Accumulated Impairment Loss Net Carrying Value as of December 31, 2016 Trademarks 15 $ 7,100 $ (1,631 ) $ (4,179 ) $ 1,290 Existing technology 13 12,600 (4,141 ) (4,328 ) 4,131 Customer relationships 11 33,500 (12,819 ) (10,751 ) 9,930 Patents 8 6,316 (713 ) — 5,603 Total intangible assets $ 59,516 $ (19,304 ) $ (19,258 ) $ 20,954 1 The fair value of reacquired rights obtained from distributor acquisitions during the first quarter of fiscal year 2017 is valued using the income approach. In addition, we effectively settled the pre-existing relationship with the distributors by assessing whether the distributor agreements include favorable or unfavorable terms compared to current market rates. Based on the assessment, we determined that the distributor agreements had terms that are consistent with market rates and, therefore, no settlement gains or losses are recorded associated with the acquisition.
Schedule of Future Amortization for Finited-Lived Intangible Assets	The total estimated future amortization expense for these acquired intangible assets as of December 31, 2017 is as follows (in thousands): Fiscal Year 2018 $ 6,379 2019 6,265 2020 3,869 2021 3,389 2022 2,116 Thereafter 2,436 Total $ 24,454

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Lease Payments	Minimum future lease payments for non-cancelable leases as of December 31, 2017 , are as follows (in thousands): Fiscal Year Operating Leases 2018 $ 14,799 2019 13,260 2020 9,759 2021 8,137 2022 6,027 Thereafter 9,573 Total minimum lease payments $ 61,555

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Stock-based Compensation Expense	The stock-based compensation related to all of our stock-based awards and employee stock purchases for the year ended December 31, 2017 , 2016 and 2015 is as follows (in thousands): For the Year Ended December 31, 2017 2016 2015 Cost of net revenues $ 3,330 $ 3,966 $ 3,938 Selling, general and administrative 46,550 42,612 40,813 Research and development 8,974 7,570 8,192 Total stock-based compensation $ 58,854 $ 54,148 $ 52,943
Stock Option Activity	Activity for the year ended December 31, 2017 , under the stock option plans is set forth below: Stock Options Number of Shares Underlying Stock Options (in thousands) Weighted Average Exercise Price per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 222 $ 14.90 Granted — — Exercised (143 ) 16.66 Cancelled or expired (4 ) 18.16 Outstanding as of December 31, 2017 75 $ 11.36 0.93 $ 15,752 Vested and expected to vest at December 31, 2017 75 $ 11.36 0.93 $ 15,752 Exercisable at December 31, 2017 75 $ 11.36 0.93 $ 15,752
Fair value assumptions using the Monte Carlo simulation	The following weighted-average assumptions used in the Monte Carlo simulation were as follows: Year Ended December 31, 2017 2016 2015 Expected term (in years) 3.0 3.0 3.0 Expected volatility 28.9 % 34.0 % 36.9 % Risk-free interest rate 1.5 % 0.9 % 1.0 % Expected dividends — — — Weighted average fair value per share at grant date $ 120.39 $ 68.88 $ 61.73
Schedule of ESPP share activity	The following table summarizes the ESPP shares issued: Year Ended December 31, 2017 2016 2015 Number of shares issued (in thousands) 202 197 230 Weighted average price $ 59.93 $ 48.65 $ 36.66
2001 Purchase Plan
Weighted Average Assumptions Used for the Fair Value of Options Component of Purchase Plan Granted Estimated at Grant Date	The fair value of the option component of the 2010 Purchase Plan shares was estimated at the grant date using the Black-Scholes option pricing model with the following weighted average assumptions: Year Ended December 31, 2017 2016 2015 Expected term (in years) 1.2 1.2 1.2 Expected volatility 26.8 % 30.5 % 31.1 % Risk-free interest rate 1.0 % 0.7 % 0.3 % Expected dividends — — — Weighted average fair value at grant date $ 31.36 $ 22.23 $ 16.19
Stock Option
Weighted Average Assumptions Used for the Fair Value of Options Component of Purchase Plan Granted Estimated at Grant Date	Activity for the year ended December 31, 2017 , under the stock option plans is set forth below: Stock Options Number of Shares Underlying Stock Options (in thousands) Weighted Average Exercise Price per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 222 $ 14.90 Granted — — Exercised (143 ) 16.66 Cancelled or expired (4 ) 18.16 Outstanding as of December 31, 2017 75 $ 11.36 0.93 $ 15,752 Vested and expected to vest at December 31, 2017 75 $ 11.36 0.93 $ 15,752 Exercisable at December 31, 2017 75 $ 11.36 0.93 $ 15,752
Restricted Stock Units (RSUs)
Summary of Nonvested Shares	A summary for the year ended December 31, 2017 , is as follows: Shares Underlying RSUs (in thousands) Weighted Average Grant Date Fair Value Weighted Remaining Vesting Period (in years) Aggregate Intrinsic Value (in thousands) Nonvested as of December 31, 2016 1,789 $ 58.39 Granted 487 118.77 Vested and released (852 ) 54.24 Forfeited (83 ) 69.06 Nonvested as of December 31, 2017 1,341 $ 82.30 1.18 $ 297,973
Market Performance Based Restricted Stock Units
Summary of Nonvested Shares	The following table summarizes the MSU performance as of December 31, 2017 : Number of Shares Underlying MSUs (in thousands) Weighted Average Grant Date Fair Value Weighted Average Remaining Vesting Period (in years) Aggregate Intrinsic Value (in thousands) Nonvested as of December 31, 2016 520 $ 60.49 Granted 201 88.80 Vested and released (283 ) 53.11 Forfeited (10 ) 64.50 Nonvested as of December 31, 2017 428 $ 78.53 0.97 $ 95,120

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	income before provision for income taxes and equity in losses of investee consists of the following (in thousands): Year ended December 31, 2017 2016 2015 Domestic $ 123,696 $ 118,871 $ 87,803 Foreign 241,103 123,695 98,298 Net income before provision for income taxes and equity in losses of investee $ 364,799 $ 242,566 $ 186,101
Schedule of Components of Income Tax Expense (Benefit)	The provision for income taxes consists of the following (in thousands): Year Ended December 31, 2017 2016 2015 Federal Current $ 91,214 $ 40,235 $ 28,596 Deferred 15,724 24,794 6,679 106,938 65,029 35,275 State Current 2,580 2,603 3,271 Deferred 2,677 2,636 (703 ) 5,257 5,239 2,568 Foreign Current 15,285 8,964 4,305 Deferred 2,682 (28,032 ) (67 ) 17,967 (19,068 ) 4,238 Provision for income taxes $ 130,162 $ 51,200 $ 42,081
Schedule of Effective Income Tax Rate Reconciliation	The differences between income taxes using the federal statutory income tax rate of 35% and our effective tax rate are as follows: Year Ended December 31, 2017 2016 2015 U.S. federal statutory income tax rate 35.0 % 35.0 % 35.0 % State income taxes, net of federal tax benefit 1.4 2.1 1.5 Impact of U.S. Tax Cuts and Jobs Act 23.1 — — Impact of differences in foreign tax rates (18.0 ) (6.3 ) (16.2 ) Valuation allowance release for Israel — (12.9 ) — Stock-based compensation (6.3 ) 1.2 1.6 Other items not individually material 0.5 2.0 0.7 35.7 % 21.1 % 22.6 %
Schedule of Deferred Tax Assets and Liabilities	As of December 31, 2017 and 2016 , the significant components of our deferred tax assets and liabilities are (in thousands): Year Ended December 31, 2017 2016 Deferred tax assets: Net operating loss and capital loss carryforwards $ 24,971 $ 25,445 Reserves and accruals 12,547 22,954 Stock-based compensation 10,074 16,399 Deferred revenue 10,811 13,975 Net translation losses 1,928 1,634 Credit carryforwards 792 679 61,123 81,086 Deferred tax liabilities: Depreciation and amortization 7,522 12,034 Unremitted foreign earnings 3,305 — Prepaid expenses 751 969 11,578 13,003 Net deferred tax assets before valuation allowance 49,545 68,083 Valuation allowance (278 ) (256 ) Net deferred tax assets $ 49,267 $ 67,827
Schedule of Unrecognized Tax Benefits Rollforward	The changes in the balance of gross unrecognized tax benefits, which exclude interest and penalties, for the year ended December 31, 2017 , 2016 and 2015 , are as follows (in thousands): Unrecognized tax benefit as of December 31, 2014 $ 33,067 Tax positions related to current year: Additions for uncertain tax positions 6,346 Unrecognized tax benefit as of December 31, 2015 39,413 Tax positions related to current year: Additions for uncertain tax positions 6,971 Unrecognized tax benefit as of December 31, 2016 46,384 Tax positions related to current year: Additions for uncertain tax positions 1,819 Tax positions related to prior year: Additions for uncertain tax positions 1,809 Decreases for uncertain tax positions (826 ) Settlements with tax authorities (1,527 ) Reductions due to lapse of applicable statute of limitations (3 ) Unrecognized tax benefit as of December 31, 2017 $ 47,656

Net Profit per Share (Tables)

Net Profit per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Earnings Per Share Basic And Diluted	The following table sets forth the computation of basic and diluted net income per share attributable to common stock (in thousands, except per share amounts): Year Ended December 31, 2017 2016 2015 Numerator: Net income $ 231,418 $ 189,682 $ 144,020 Denominator: Weighted-average common shares outstanding, basic 80,085 79,856 79,998 Dilutive effect of potential common stock 1,747 1,628 1,523 Total shares, diluted 81,832 81,484 81,521 Net income per share, basic $ 2.89 $ 2.38 $ 1.80 Net income per share, diluted $ 2.83 $ 2.33 $ 1.77

Supplemental Cash Flow Inform33

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	The supplemental cash flow information consists of the following (in thousands): Year Ended December 31, 2017 2016 2015 Taxes paid $ 51,231 $ 47,289 $ 40,621 Non-cash investing activities: Fixed assets acquired with accounts payable or accrued liabilities $ 15,105 $ 4,434 $ 14,636 Fair value of option to purchase property $ 3,936 $ — $ —

Segments and Geographical Inf34

Segments and Geographical Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	These reportable operating segments are based on how our CODM views and evaluates our operations as well as allocation of resources. The following information relates to these segments (in thousands): For the Year Ended December 31, Net revenues 2017 2016 2015 Clear Aligner $ 1,309,262 $ 958,327 $ 800,186 Scanner 164,151 121,547 45,300 Total net revenues $ 1,473,413 $ 1,079,874 $ 845,486 Gross profit Clear Aligner $ 1,019,563 $ 747,494 $ 628,187 Scanner 97,384 67,800 11,923 Total gross profit $ 1,116,947 $ 815,294 $ 640,110 Income from operations Clear Aligner $ 564,648 $ 411,817 $ 371,113 Scanner 49,613 37,498 (12,337 ) Unallocated corporate expenses (260,650 ) (200,394 ) (170,142 ) Total income from operations $ 353,611 $ 248,921 $ 188,634 Depreciation and amortization Clear Aligner $ 21,581 $ 13,742 $ 9,842 Scanner 4,385 3,871 3,839 Unallocated corporate expenses 11,773 6,389 4,323 Total depreciation and amortization $ 37,739 $ 24,002 $ 18,004 The following table reconciles total segment income from operations in the table above to net income before provision for income taxes and equity losses of investee (in thousands): For the Year Ended December 31, 2017 2016 2015 Total segment income from operations $ 614,261 $ 449,315 $ 358,776 Unallocated corporate expenses (260,650 ) (200,394 ) (170,142 ) Total income from operations 353,611 248,921 188,634 Interest and other income (expense), net 11,188 (6,355 ) (2,533 ) Net income before provision for income taxes and equity losses of investee $ 364,799 $ 242,566 $ 186,101
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	Net revenues are presented below by geographic area (in thousands): For the Year Ended December 31, 2017 2016 2015 Net revenues (1) : United States (2) $ 836,200 $ 692,254 $ 585,874 The Netherlands (2) 456,108 286,911 167,128 Other International 181,105 100,709 92,484 Total net revenues $ 1,473,413 $ 1,079,874 $ 845,486 (1) Net revenues are attributed to countries based on location of where revenue is recognized. (2) Effective July 2016, we implemented a new international corporate structure. This changed the structure of our international procurement and sales operations. Tangible long-lived assets are presented below by geographic area (in thousands): As of December 31, 2017 2016 Long-lived assets (1) : The Netherlands $ 143,673 $ 104,039 United States 128,171 43,278 Costa Rica 30,738 2,657 Mexico 25,090 17,918 China 5,480 461 Other International 15,641 6,814 Total long-lived assets $ 348,793 $ 175,167 (1) Long-lived assets are attributed to countries based on entity that owns the assets.

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)stagesegmentfinancial_institutionaligner	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | segment			2
Accrued liabilities	$ 194,198		$ 194,198	$ 134,332
Restricted Cash and Cash Equivalents				3,700
Original maturity of highly liquid investments included in Cash and cash equivalents			40 months
Foreign currency net gains (losses)			$ 9,000	(8,000)	$ (4,000)
Number of financial instutions used | financial_institution			3
Capitalized software costs				13,200
Scanners, Warranty period			1 year
Treatment Plans, Period For Additional Replacements For No Charge			5 years
Treatment Plans, Number Of Optional Replacements | aligner			6
Treatment Plan, Number Of Batches/Stages | stage			9
Advertising cost			$ 70,000	36,000	$ 23,400
Lease term			9 years
Additional income tax expense due to TCJA	84,300
Deferred tax asset due to TCJA	10,400
Deferred tax liability due to TCJA	73,900
Undistributed earnings of foreign subsidiaries	$ 606,500		$ 606,500
Minimum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles			1 year
Maximum
Significant Accounting Policies [Line Items]
Original maturity of highly liquid investments included in Cash and cash equivalents			3 months
Estimated useful lives of intangibles			15 years
Other Noncurrent Assets
Significant Accounting Policies [Line Items]
Restricted cash				3,300
Other Current Assets
Significant Accounting Policies [Line Items]
Restricted cash				$ 400
Accounting Standards Update 2016-09
Significant Accounting Policies [Line Items]
Tax benefit			$ 30,000
Retained Earnings (Deficit) | Accounting Standards Update 2016-16
Significant Accounting Policies [Line Items]
Decrease to retained earnings		$ (1,300)

Marketable Securities and Fai36

Marketable Securities and Fair Value Measurements - Short-term and Long-term Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 272,280	$ 251,086
Gross Unrealized Gains	3	38
Gross Unrealized Losses	(252)	(143)
Fair Value	272,031	250,981
Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	58,503	42,397
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(6)
Fair Value	58,502	42,391
Short-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	145,728	122,788
Gross Unrealized Gains	3	22
Gross Unrealized Losses	(174)	(121)
Fair Value	145,557	122,689
Short-term Investments | Municipal Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		5,852
Gross Unrealized Gains		0
Gross Unrealized Losses		(5)
Fair Value		5,847
Short-term Investments | U.S. government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,013	28,903
Gross Unrealized Gains	0	9
Gross Unrealized Losses	(7)	(4)
Fair Value	3,006	28,908
Short-term Investments | U.S. Government Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	60,650	45,146
Gross Unrealized Gains	0	7
Gross Unrealized Losses	(70)	(7)
Fair Value	60,580	45,146
Short-term Investments | Certificates of Deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,386	6,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	4,386	6,000
Long Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,090	59,887
Gross Unrealized Gains	2	13
Gross Unrealized Losses	(144)	(117)
Fair Value	39,948	59,783
Long Term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,067	40,889
Gross Unrealized Gains	2	8
Gross Unrealized Losses	(76)	(85)
Fair Value	24,993	40,812
Long Term Investments | U.S. government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,023	6,805
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(68)	(16)
Fair Value	$ 14,955	6,789
Long Term Investments | Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		177
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		177
Long Term Investments | U.S. Government Treasury Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		12,016
Gross Unrealized Gains		5
Gross Unrealized Losses		(16)
Fair Value		$ 12,005

Marketable Securities and Fai37

Marketable Securities and Fair Value Measurements - Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments, All Other Investments [Abstract]
One year or less	$ 272,031	$ 250,981
One year through two years	39,948	59,783
Marketable Securities	$ 311,979	$ 310,764

Marketable Securities and Fai38

Marketable Securities and Fair Value Measurements - Unobservable Input Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 2,047
Additional notes receivable issued	2,000
Accrued interest receivable	79
Change in fair value recognized in earnings	350
Ending balance	$ 4,476

Marketable Securities and Fai39

Marketable Securities and Fair Value Measurements - Fair Value Measured On A Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	$ 272,031	$ 250,981
Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	39,948	59,783
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Notes Receivable, Fair Value Disclosure	4,476	2,047
Assets measured at fair value	581,947	406,195
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Notes Receivable, Fair Value Disclosure	0	0
Assets measured at fair value	313,735	144,330
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Notes Receivable, Fair Value Disclosure	0	0
Assets measured at fair value	263,736	259,818
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Notes Receivable, Fair Value Disclosure	4,476	2,047
Assets measured at fair value	4,476	2,047
Money market funds | Fair Value, Measurements, Recurring | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	253,155	87,179
Money market funds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	253,155	87,179
Money market funds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	0	0
Commercial paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	58,502	42,391
Commercial paper | Fair Value, Measurements, Recurring | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	7,246	2,499
Commercial paper | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	58,502	42,391
Commercial paper | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	0	0
Commercial paper | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	0	0
Commercial paper | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	7,246	2,499
Commercial paper | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	58,502	42,391
Corporate bonds | Fair Value, Measurements, Recurring | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	2,016	750
Corporate bonds | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	145,557	122,689
Corporate bonds | Fair Value, Measurements, Recurring | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	24,993	40,812
Corporate bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	0	0
Corporate bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	0	0
Corporate bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	0	0
Corporate bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money market funds	2,016	750
Corporate bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	145,557	122,689
Corporate bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	24,993	40,812
U.S. government agency bonds | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	3,006	28,908
U.S. government agency bonds | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	14,955	6,789
U.S. government agency bonds | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	3,006	28,908
U.S. government agency bonds | Fair Value, Measurements, Recurring | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	14,955	6,789
U.S. government agency bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	0	0
U.S. government agency bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	0	0
U.S. government agency bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	3,006	28,908
U.S. government agency bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	14,955	6,789
Israeli funds | Fair Value, Measurements, Recurring | Other assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Other assets	3,075	2,956
Israeli funds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Other assets	0	0
Israeli funds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Other assets	3,075	2,956
Municipal Securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		5,847
Municipal Securities | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		5,847
Municipal Securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		0
Municipal Securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		5,847
Asset-backed Securities | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		177
Asset-backed Securities | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		45,146
Asset-backed Securities | Fair Value, Measurements, Recurring | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		177
Asset-backed Securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		45,146
Asset-backed Securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		0
Asset-backed Securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		0
Asset-backed Securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		177
Certificates of Deposit | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	4,386	6,000
Certificates of Deposit | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	4,386	6,000
Certificates of Deposit | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	0	0
Certificates of Deposit | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	4,386	6,000
U.S. Government Treasury Bonds | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	60,580	45,146
U.S. Government Treasury Bonds | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		12,005
U.S. Government Treasury Bonds | Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	60,580
U.S. Government Treasury Bonds | Fair Value, Measurements, Recurring | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		12,005
U.S. Government Treasury Bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	60,580
U.S. Government Treasury Bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		12,005
U.S. Government Treasury Bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments	$ 0
U.S. Government Treasury Bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long Term Investments
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments		$ 0

Marketable Securities and Fai40

Marketable Securities and Fair Value Measurements - Narrative (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Original maturity of highly liquid investments included in Cash and cash equivalents	40 months
Weighted average maturity	6 months	7 months

Balance Sheet Components - Inve

Balance Sheet Components - Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet Related Disclosures [Abstract]
Raw materials	$ 12,721	$ 9,793
Work in process	12,157	10,773
Finished goods	6,810	6,565
Inventories	$ 31,688	$ 27,131

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment, Net [Abstract]
Property and equipment	$ 484,601	$ 310,881
Less: Accumulated depreciation and amortization	(135,808)	(135,714)
Property, plant and equipment, net	348,793	175,167
Depreciation and amortization	37,700	24,000	$ 18,000
Clinical and manufacturing equipment
Property, Plant and Equipment, Net [Abstract]
Property and equipment	183,392	153,938
Computer hardware
Property, Plant and Equipment, Net [Abstract]
Property and equipment	24,933	27,978
Computer software
Property, Plant and Equipment, Net [Abstract]
Property and equipment	54,756	59,997
Furniture and fixtures
Property, Plant and Equipment, Net [Abstract]
Property and equipment	16,271	10,306
Leasehold improvements
Property, Plant and Equipment, Net [Abstract]
Property and equipment	37,756	22,370
Building
Property, Plant and Equipment, Net [Abstract]
Property and equipment	63,887	7,272
Land
Property, Plant and Equipment, Net [Abstract]
Property and equipment	17,630	3,072
Construction in progress
Property, Plant and Equipment, Net [Abstract]
Property and equipment	$ 85,976	$ 25,948

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet Related Disclosures [Abstract]
Accrued payroll and benefits	$ 103,004	$ 79,214
Accrued expenses	27,318	21,811
Accrued income taxes	12,405	4,210
Accrued sales rebate	11,209	10,342
Accrued professional fees	6,316	3,604
Accrued warranty	5,929	3,841
Accrued sales tax and value added tax	5,503	5,032
Other accrued liabilities	22,514	6,278
Total current accrued liabilities	$ 194,198	$ 134,332

Balance Sheet Components - Warr

Balance Sheet Components - Warranty Accrual Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 3,841	$ 2,638
Charged to cost of revenues	7,195	4,894
Actual warranty expenditures	(5,107)	(3,691)
Balance at end of period	$ 5,929	$ 3,841

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Scanners, Warranty period	1 year

Equity Method Investments (Deta

Equity Method Investments (Details) - USD ($) $ in Thousands		Feb. 07, 2018	Jul. 24, 2017	Jul. 25, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Ownership				17.00%
Payments to acquire				$ 46,700	$ 12,764	$ 46,745	$ 0
Equity method investment					54,606	45,061
Net revenues	[1]				1,473,413	1,079,874	845,486
Loan repayment from equity investee					6,000	0	$ 0
SDC
Schedule of Equity Method Investments [Line Items]
Ownership			19.00%
Additional ownership acquired			2.00%
Payments to acquire			$ 12,800
Equity method investment					54,600	45,100
Due from related parties					14,300	100
Net revenues					24,100	$ 200
Loan agreement reached			$ 30,000
Loan receivable					$ 30,000
Subsequent Event | SDC
Schedule of Equity Method Investments [Line Items]
Loan receivable		$ 30,000
Loan repayment from equity investee		$ 30,000
[1]	Long-lived assets are attributed to countries based on entity that owns the assets.

Business Combinations - Additio

Business Combinations - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill and intangible assets, net		$ 64,614	$ 61,044	$ 61,074
Certain Distributors
Business Acquisition [Line Items]
Cash consideration	$ 9,500
Net tangible liabilities	1,900
Intangibles acquired	8,200
Goodwill and intangible assets, net	$ 3,200

Goodwill and Intangible Asset48

Goodwill and Intangible Assets - Change in the Carrying Value of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance, Beginning Balance	$ 61,044	$ 61,074
Adjustments	323	(30)	[1]
Goodwill from distributor acquisitions	3,247
Balance, Ending Balance	$ 64,614	$ 61,044
[1]	The adjustments to goodwill during the period were related to foreign currency translation and/or purchase accounting adjustments within the measurement period.

Goodwill and Intangible Asset49

Goodwill and Intangible Assets - Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 68,116	$ 59,516
Accumulated Amortization	(24,404)	(19,304)
Accumulated Impairment Loss	(19,258)	(19,258)
Total	$ 24,454	$ 20,954
Trademarks
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives of intangibles	15 years	15 years
Gross Carrying Amount	$ 7,100	$ 7,100
Accumulated Amortization	(1,769)	(1,631)
Accumulated Impairment Loss	(4,179)	(4,179)
Total	$ 1,152	$ 1,290
Existing technology
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives of intangibles	13 years	13 years
Gross Carrying Amount	$ 12,600	$ 12,600
Accumulated Amortization	(4,704)	(4,141)
Accumulated Impairment Loss	(4,328)	(4,328)
Total	$ 3,568	$ 4,131
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives of intangibles	11 years	11 years
Gross Carrying Amount	$ 33,500	$ 33,500
Accumulated Amortization	(14,681)	(12,819)
Accumulated Impairment Loss	(10,751)	(10,751)
Total	$ 8,068	$ 9,930
Distribution Rights
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives of intangibles	3 years
Gross Carrying Amount	$ 7,500
Accumulated Amortization	(1,356)
Accumulated Impairment Loss	0
Total	$ 6,144
Patents
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives of intangibles	8 years	8 years
Gross Carrying Amount	$ 6,798	$ 6,316
Accumulated Amortization	(1,504)	(713)
Accumulated Impairment Loss	0	0
Total	$ 5,294	$ 5,603
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives of intangibles	2 years
Gross Carrying Amount	$ 618
Accumulated Amortization	(390)
Accumulated Impairment Loss	0
Total	$ 228

Goodwill and Intangible Asset50

Goodwill and Intangible Assets - Total Estimated Annual Future Amortization Expense for the Acquired Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 6,379
2,019	6,265
2,020	3,869
2,021	3,389
2,022	2,116
Thereafter	2,436
Total	$ 24,454	$ 20,954

Credit Facility - Additional In

Credit Facility - Additional Information (Detail) - USD ($)	Feb. 16, 2018	Dec. 31, 2017	Mar. 22, 2013
Line of Credit Facility [Line Items]
Line of credit, available borrowings			$ 50,000,000
Current borrowing capacity			$ 10,000,000
Interest rate on borrowings		1.75%
Line of credit, amount outstanding		$ 0
Subsequent Event
Line of Credit Facility [Line Items]
Line of credit, available borrowings	$ 200,000,000
Current borrowing capacity	$ 50,000,000
Base rate | Subsequent Event
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Base rate | Subsequent Event | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.25%
Base rate | Subsequent Event | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.75%
LIBOR rate | Subsequent Event
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
LIBOR rate | Subsequent Event | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.25%
LIBOR rate | Subsequent Event | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.75%

Legal Proceedings (Details)

Legal Proceedings (Details)	Nov. 14, 2017Lawsuit
Gain Contingencies [Line Items]
Patents allegedly infringed upon	26
Lawsuit against 3Shape A/S
Gain Contingencies [Line Items]
Number of lawsuits/complaints	6
3Shape violation of trade laws
Gain Contingencies [Line Items]
Number of lawsuits/complaints	2
Patent infringement by 3Shape
Gain Contingencies [Line Items]
Number of lawsuits/complaints	4

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions

Nov. 15, 2017

Nov. 09, 2017

Jul. 24, 2017

Jun. 30, 2017

Jul. 25, 2016

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Feb. 07, 2018

Jan. 08, 2018

Nov. 27, 2017

Jun. 05, 2017

Other Commitments [Line Items]

Total rent expense

$ 13.8

$ 9.9

$ 8.2

Loans And Leases Receivable, Commitments, Fixed Rates, State Rate

7.00%

Interest rate on borrowings at LIBOR plus

1.75%

Software

$ 50

Software term

3 years

Minimum purchase amount commitment

$ 305.2

Commitments To Purchase Convertible Promissory Notes With Privately Held Company [Member]

Other Commitments [Line Items]

Other commitment

$ 5

Other Commitments, Future Minimum Payments, Remainder of Fiscal Year

2

$ 2

Other Commitment, Due in Second Year

$ 1

Interest rate on borrowings at LIBOR plus

2.50%

SDC

Other Commitments [Line Items]

Loans And Leases Receivable, Borrowing Base As A Percentage Of Accounts Receivable

80.00%

Maximum | SDC

Other Commitments [Line Items]

Loans and Leases Receivable, Commitments, Fixed Rates

$ 30

$ 15

SDC

Other Commitments [Line Items]

Loan receivable

$ 30

Belen Business Center

Other Commitments [Line Items]

Consideration transferred

$ 26.1

Deposit

20.9

Ziyang, China

Other Commitments [Line Items]

Committed investment minimum

$ 46

Costa Rica

Other Commitments [Line Items]

Consideration transferred

$ 25.6

Deposit

$ 6.8

Subsequent Event

Other Commitments [Line Items]

Deposit

$ 5.2

Subsequent Event | SDC

Other Commitments [Line Items]

Loan receivable

$ 30

Commitments and Contingencies54

Commitments and Contingencies - Minimum Future Lease Payments for Non-Cancelable Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 14,799
2,019	13,260
2,020	9,759
2,021	8,137
2,022	6,027
Thereafter	9,573
Total minimum lease payments	$ 61,555

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)purchase_period$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	May 16, 2013shares
Stockholders Equity Note [Line Items]
Preferred stock, par value (usd per share) | $ / shares	$ 0.0001	$ 0.0001
Total intrinsic value of stock options exercised | $	$ 18,100	$ 18,200	$ 7,400
Employees’ taxes paid upon the vesting of restricted stock units | $	$ (46,168)	$ (29,857)	$ (20,716)
Employee Stock Purchase Plan, Duration Of Offering Period	24 months
Number of offering periods | purchase_period	4
Number of shares issued (in thousands)	202,000	197,000	230,000
Stock-based compensation expense | $	$ 58,854	$ 54,148	$ 52,943
Stockholder Rights Plan
Stockholders Equity Note [Line Items]
Number of shares called by each right (shares)	0.001
Amended And Restated 2005 Stock Incentive Plan
Stockholders Equity Note [Line Items]
Shares reserved for issuance	6,885,248
2001 Purchase Plan
Stockholders Equity Note [Line Items]
Employee stock purchase plan, purchase price as percentage of fair market value of common stock	85.00%
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
Vested rand released in period, Total intrinsic value | $	$ 99,500	59,800	45,900
Vested in period, Fair value | $	$ 46,200	$ 39,100	$ 30,000
Granted (usd per share) | $ / shares	$ 118.77	$ 67.82	$ 57.78
Total unamortized compensation cost | $	$ 72,900
Weighted average period of total unamortized cost	2 years 1 month 6 days
Restricted stock units, shares vested and released (shares)	851,693
Restricted stock units, shares withheld for tax payments	287,790
Restricted stock units, net issuance	563,903
Stock Options | Incentive Plan 2005
Stockholders Equity Note [Line Items]
Weighted award against authorized maximum (shares)	25% vesting one year from the date of grant and 1/48th each month thereafter
Market Performance Based Restricted Stock Units
Stockholders Equity Note [Line Items]
Vested rand released in period, Total intrinsic value | $	$ 28,800	$ 17,400	$ 9,200
Vested in period, Fair value | $	$ 15,000	9,900	4,900
Granted (usd per share) | $ / shares	$ 88.80
Total unamortized compensation cost | $	$ 12,200
Weighted average period of total unamortized cost	1 year
Restricted stock units, shares vested and released (shares)	282,548
Restricted stock units, shares withheld for tax payments	118,562
Restricted stock units, net issuance	163,986
Market Performance Based Restricted Stock Units | Minimum
Stockholders Equity Note [Line Items]
Stock incentive plan, vesting period	2 years
Market Performance Based Restricted Stock Units | Maximum
Stockholders Equity Note [Line Items]
Stock incentive plan, vesting period	3 years
Percentage of market-performance based restricted stock units eligible to vest over the vesting period	200.00%
Employee Stock Purchase Plan 2010
Stockholders Equity Note [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award Shares Remaining Available For Issuance	735,301
Employee Stock Incentive Plan 2005
Stockholders Equity Note [Line Items]
Number of shares available for grant (shares)				27,783,379
Share-based Compensation Arrangement by Share-based Payment Award, Weight Of Awarded Shares Against Authorized Maximum	1.9			1.5
Employee Stock Purchase Plan 2010 | Maximum
Stockholders Equity Note [Line Items]
Maximum number of shares available	2,400,000
Employee Stock Purchase Plan
Stockholders Equity Note [Line Items]
Total unamortized compensation cost | $	$ 2,700
Weighted average period of total unamortized cost	7 months 6 days
Stock-based compensation expense | $	$ 5,400	$ 2,700	$ 4,100
Monthly Vesting | Stock Options | Incentive Plan 2005
Stockholders Equity Note [Line Items]
Stock incentive plan, vesting percentage	2.08%

Stockholders' Equity - Stock-Ba

Stockholders' Equity - Stock-Based Awards and Employee Stock Purchases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 58,854	$ 54,148	$ 52,943
Cost of net revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,330	3,966	3,938
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	46,550	42,612	40,813
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 8,974	$ 7,570	$ 8,192

Stockholders' Equity - Activity

Stockholders' Equity - Activity Under Stock Option Plans (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Number of Shares Underlying Stock Options
Outstanding beginning balance (shares) | shares	222
Granted (shares) | shares	0
Exercised (shares) | shares	(143)
Cancelled or expired (shares) | shares	(4)
Outstanding ending balance (shares) | shares	75
Vested and expected to vest at December 31, 2013 (shares) | shares	75
Exercisable at December 31, 2013 (shares) | shares	75
Weighted Average Exercise Price per Share
Outstanding beginning balance (usd per share) | $ / shares	$ 14.90
Granted (usd per share) | $ / shares	0
Exercised (usd per share) | $ / shares	16.66
Cancelled or expired (usd per share) | $ / shares	18.16
Outstanding ending balance (usd per share) | $ / shares	11.36
Vested and expected to vest at December 31, 2013 (usd per share) | $ / shares	11.36
Exercisable at December 31, 2013 (usd per share) | $ / shares	$ 11.36
Weighted Average Remaining Contractual Term (in years)
Outstanding as of December 31, 2017	11 months 5 days
Vested and expected to vest at December 31, 2017	11 months 5 days
Exercisable at December 31, 2017	11 months 5 days
Aggregate Intrinsic Value
Outstanding as of December 31, 2017 | $	$ 15,752
Vested and expected to vest at December 31, 2017 | $	15,752
Exercisable at December 31, 2017 | $	$ 15,752

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Nonvested Shares (Detail) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares Underlying RSUs
Nonvested beginning balance (shares)	1,789,000
Granted (shares)	487,000
Vested and released (shares)	(851,693)
Forfeited (shares)	(83,000)
Nonvested ending balance (shares)	1,341,000	1,789,000
Nonvested, beginning balance (usd per share)	$ 58.39
Granted (usd per share)	118.77	$ 67.82	$ 57.78
Vested and released (usd per share)	54.24
Forfeited (usd per share)	69.06
Nonvested, ending balance (usd per share)	$ 82.30	$ 58.39
Weighted Remaining Vesting Period (in years)
Nonvested as of December 31, 2017	1 year 2 months 5 days
Aggregate Intrinsic Value
Nonvested as of December 31, 2017	$ 297,973

Stockholders' Equity - Summar59

Stockholders' Equity - Summary of MSU Performance (Detail) - Market Performance Based Restricted Stock Units - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Nonvested beginning balance (shares)	520,000
Granted (shares)	201,000
Vested and released (shares)	(282,548)
Forfeited (shares)	(10,000)
Nonvested ending balance (shares)	428,000	520,000
Nonvested (usd per share)	$ 78.53	$ 60.49
Granted (usd per share)	88.80
Vested and released (usd per share)	53.11
Forfeited (usd per share)	$ 64.50
Weighted Average Remaining Contractual Term
Nonvested	11 months 19 days
Aggregate Intrinsic Value
Nonvested	$ 95,120

Stockholders' Equity - Weighted

Stockholders' Equity - Weighted-Average Assumptions Used in the Monte Carlo Simulation (Detail) - Market Performance Based Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	3 years	3 years	3 years
Expected volatility	28.90%	34.00%	36.90%
Risk-free interest rate	1.50%	0.90%	1.00%
Expected dividends	0.00%	0.00%	0.00%
Weighted average fair value per share at grant date (usd per share)	$ 120.39	$ 68.88	$ 61.73

Stockholders' Equity - ESPP Act

Stockholders' Equity - ESPP Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Number of shares issued (in thousands)	202	197	230
Weighted average price	$ 59.93	$ 48.65	$ 36.66

Stockholders' Equity - Weight62

Stockholders' Equity - Weighted Average Assumptions Used for the Fair Value of the Option Component of the Purchase Plan Shares Estimated at Grant Date Using Black-Scholes Option Pricing Model (Detail) - Employee Stock Purchase Plan - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	1 year 2 months 12 days	1 year 2 months 12 days	1 year 2 months 12 days
Expected volatility	26.80%	30.50%	31.10%
Risk-free interest rate	1.00%	0.70%	0.30%
Expected dividends	0.00%	0.00%	0.00%
Weighted average fair value at grant date (usd per share)	$ 31.36	$ 22.23	$ 16.19

Common Stock Repurchase Progr63

Common Stock Repurchase Program - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands	May 04, 2016	Apr. 28, 2015	Apr. 23, 2014	Feb. 28, 2018	Aug. 31, 2017	Jul. 23, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 28, 2016
Share Repurchases [Line Items]
Common stock repurchased and retired							$ 103,793,000	$ 96,218,000	$ 101,791,000
Additional Paid-in Capital
Share Repurchases [Line Items]
Common stock repurchased and retired							5,583,000	10,593,000	15,669,000
Retained Earnings
Share Repurchases [Line Items]
Common stock repurchased and retired							98,210,000	$ 85,625,000	$ 86,122,000
April 2014 Stock Repurchase Program
Share Repurchases [Line Items]
Repurchase of common stock, common stock authorized			$ 300,000,000
Repurchase period			3 years
Common stock repurchased and retired (shares)								500
Common stock repurchased (in dollars per share)								$ 58.89
Common stock repurchased and retired							$ 3,800,000	$ 31,800,000
Accelerated share repurchase agreement amount	$ 50,000,000	$ 70,000,000
Accelerated share repurchase (in shares)						1,200	40
Accelerated share repurchases price per share (in dollars per share)						$ 60.52	$ 96.37
April 2016 Stock Repurchase Program
Share Repurchases [Line Items]
Repurchase of common stock, common stock authorized										$ 300,000,000
Common stock repurchased and retired (shares)								500
Common stock repurchased (in dollars per share)								$ 92.58
Common stock repurchased and retired								$ 46,200,000
Accelerated share repurchase (in shares)								600
Accelerated share repurchases price per share (in dollars per share)								$ 81.89
2017 ASR
Share Repurchases [Line Items]
Common stock repurchased and retired (shares)					400		200
Common stock repurchased (in dollars per share)					$ 146.48		$ 243.40
Common stock repurchased and retired							$ 50,000,000
Authorized repurchase amount remaining							$ 200,000,000
Subsequent Event | 2017 ASR
Share Repurchases [Line Items]
Common stock repurchased and retired (shares)				400
Common stock repurchased and retired				$ 100,000,000
Accelerated share repurchases price per share (in dollars per share)				$ 252.24

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2009
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Accrued severance funds liability	$ 3.2	$ 3.1
Defined Contribution Pension Plan 401k
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Employer matching contribution as percentage of employee's salary deferral contributions				50.00%
Employer matching contribution as percentage of employee's eligible compensation				6.00%
Employer contributions amount	$ 4.3	$ 3.4	$ 2.7

Income Taxes - Domestic and For

Income Taxes - Domestic and Foreign Components of Income (loss) Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ 123,696	$ 118,871	$ 87,803
Foreign	241,103	123,695	98,298
Net income before provision for income taxes and equity in losses of investee	$ 364,799	$ 242,566	$ 186,101

Income Taxes Income Taxes - Pro

Income Taxes Income Taxes - Provision for (Benefit from) Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal
Current	$ 91,214	$ 40,235	$ 28,596
Deferred	15,724	24,794	6,679
Total federal income tax expense	106,938	65,029	35,275
State
Current	2,580	2,603	3,271
Deferred	2,677	2,636	(703)
Total state tax expense	5,257	5,239	2,568
Foreign
Current	15,285	8,964	4,305
Deferred	2,682	(28,032)	(67)
Total foreign tax expense	17,967	(19,068)	4,238
Provision for income taxes	$ 130,162	$ 51,200	$ 42,081

Income Taxes - Differences Betw

Income Taxes - Differences Between Income Taxes Using Federal Statutory Income Tax Rate and Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	1.40%	2.10%	1.50%
Impact of U.S. Tax Cuts and Jobs Act	23.10%	0.00%	0.00%
Impact of differences in foreign tax rates	(18.00%)	(6.30%)	(16.20%)
Valuation allowance release for Israel	0.00%	(12.90%)	0.00%
Stock-based compensation	(6.30%)	1.20%	1.60%
Other items not individually material	0.50%	2.00%	0.70%
Effective Income Tax Rate, Continuing Operations, Total	35.70%	21.10%	22.60%

Income Taxes Income Taxes - Def

Income Taxes Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss and capital loss carryforwards	$ 24,971	$ 25,445
Reserves and accruals	12,547	22,954
Stock-based compensation	10,074	16,399
Deferred revenue	10,811	13,975
Net translation losses	1,928	1,634
Credit carryforwards	792	679
Total deferred tax assets, gross	61,123	81,086
Deferred tax liabilities:
Depreciation and amortization	7,522	12,034
Unremitted foreign earnings	3,305	0
Prepaid expenses	751	969
Total deferred tax liabilities, gross	11,578	13,003
Net deferred tax assets before valuation allowance	49,545	68,083
Valuation allowance	(278)	(256)
Net deferred tax assets	$ 49,267	$ 67,827

Income Taxes - Rollforward of T

Income Taxes - Rollforward of Total Gross Unrecognized Tax Benefit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit as of beginning of period	$ 46,384	$ 39,413	$ 33,067
Tax positions related to current year, additions for uncertain tax positions	1,819	6,971	6,346
Tax positions related to prior year, Additions for uncertain tax positions	1,809
Tax positions related to prior year, Decreases for uncertain tax positions	(826)
Tax positions related to prior year, Settlements with tax authorities	(1,527)
Tax positions related to prior year, Reductions due to lapse of applicable statute of limitations	(3)
Unrecognized tax benefit as of end of period	$ 47,656	$ 46,384	$ 39,413

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Additional income tax expense due to TCJA	$ 84,300
Deferred tax liability due to TCJA	73,900
Deferred tax asset due to TCJA	10,400
Undistributed earnings of foreign subsidiaries	606,500	$ 606,500
Amount of no longer indefinitely reinvested foreign earnings		$ 591,900
Deferred tax liability due in event of foreign earnings being distributed		3.3
Amount of indefinitely reinvested foreign earnings	14,700	$ 14,700
Deferred tax assets, valuation allowance	278	278	$ 256
Change in valuation allowance			(31,400)
Unrecognized tax benefits that would impact effective tax rate	39,800	39,800
Unrecognized tax benefits	47,656	47,656	46,384	$ 39,413	$ 33,067
Interest and penalties expense		800	1,400
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	2,900	2,900	2,100
Expense related to restructuring			34,300
State and Local Jurisdiction
Income Taxes [Line Items]
Net operating loss carryforwards	4,100	4,100
Foreign Country
Income Taxes [Line Items]
Net operating loss carryforwards	$ 104,700	$ 104,700
Foreign Country | Costa Rica
Income Taxes [Line Items]
Tax incentives, corporate income tax rate that would apply absent the incentives		30.00%
Tax incentives, reduction in income taxes		$ 1,800	$ 19,100	$ 32,700
Tax benefit of tax holiday on net income per share (diluted) (usd per share)		$ 0.02	$ 0.23	$ 0.40

Net Profit per Share - Computat

Net Profit per Share - Computation of Basic and Diluted Net Profit Per Share Attributable to Common Stock (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 231,418	$ 189,682	$ 144,020
Denominator:
Weighted-average common shares outstanding, basic (shares)	80,085	79,856	79,998
Dilutive effect of potential common stock (shares)	1,747	1,628	1,523
Total shares, diluted (shares)	81,832	81,484	81,521
Net income per share, basic (usd per share)	$ 2.89	$ 2.38	$ 1.80
Net income per share, diluted (usd per share)	$ 2.83	$ 2.33	$ 1.77

Supplemental Cash Flow Inform72

Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Taxes paid	$ 51,231	$ 47,289	$ 40,621
Non-cash investing and financing activities:
Fixed assets acquired with accounts payable or accrued liabilities	15,105	4,434	14,636
Fair value of option to purchase property	$ 3,936	$ 0	$ 0

Segments and Geographical Inf73

Segments and Geographical Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017Segment
Segment Reporting [Abstract]
Number of reportable segments	2

Segments and Geographical Inf74

Segments and Geographical Information Segments and Geographical Information - (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue	[1]	$ 1,473,413	$ 1,079,874	$ 845,486
Gross profit		1,116,947	815,294	640,110
Operating Income (Loss)		353,611	248,921	188,634
Depreciation and amortization		37,739	24,002	18,004
Clear Aligner
Segment Reporting Information [Line Items]
Revenue		1,309,262	958,327	800,186
Scanner and Services
Segment Reporting Information [Line Items]
Revenue		164,151	121,547	45,300
Clear Aligner
Segment Reporting Information [Line Items]
Gross profit		1,019,563	747,494	628,187
Operating Income (Loss)		564,648	411,817	371,113
Depreciation and amortization		21,581	13,742	9,842
Scanners And Services
Segment Reporting Information [Line Items]
Gross profit		97,384	67,800	11,923
Operating Income (Loss)		49,613	37,498	(12,337)
Depreciation and amortization		4,385	3,871	3,839
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Operating Income (Loss)		(260,650)	(200,394)	(170,142)
Depreciation and amortization		$ 11,773	$ 6,389	$ 4,323
[1]	Long-lived assets are attributed to countries based on entity that owns the assets.

Segments and Geographical Inf75

Segments and Geographical Information - Net Revenues by Geographic Area (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating Income (Loss)		$ 353,611	$ 248,921	$ 188,634
Interest and other income (expense), net		11,188	(6,355)	(2,533)
Net income before provision for income taxes and equity in losses of investee		364,799	242,566	186,101
Net revenues	[1]	1,473,413	1,079,874	845,486
United States
Segment Reporting Information [Line Items]
Net revenues	[1]	836,200	692,254	585,874
the Netherlands
Segment Reporting Information [Line Items]
Net revenues	[1]	456,108	286,911	167,128
Other international
Segment Reporting Information [Line Items]
Net revenues	[1]	181,105	100,709	92,484
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Operating Income (Loss)		(260,650)	(200,394)	(170,142)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		$ 614,261	$ 449,315	$ 358,776
[1]	Long-lived assets are attributed to countries based on entity that owns the assets.

Segments and Geographical Inf76

Segments and Geographical Information - Long-Lived Assets by Geographic Area (Detail) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Long-Lived Assets	[1]	$ 348,793	$ 175,167
United States
Segment Reporting Information [Line Items]
Long-Lived Assets		128,171	43,278
Costa Rica
Segment Reporting Information [Line Items]
Long-Lived Assets	[2]	30,738	2,657
Mexico
Segment Reporting Information [Line Items]
Long-Lived Assets	[1]	25,090	17,918
China
Segment Reporting Information [Line Items]
Long-Lived Assets	[1]	5,480	461
the Netherlands
Segment Reporting Information [Line Items]
Long-Lived Assets	[1]	143,673	104,039
Other international
Segment Reporting Information [Line Items]
Long-Lived Assets	[1]	$ 15,641	$ 6,814
[1]	Effective July 2016, we implemented a new international corporate structure. This changed the structure of our international procurement and sales operations.
[2]	Long-lived assets are attributed to countries based on entity that owns the assets.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts and Reserves (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 4,310	$ 2,472	$ 1,563
Additions (reductions) to Costs and Expenses	9,948	8,585	8,944
Write offs	(7,080)	(6,747)	(8,035)
Balance at End of Period	7,178	4,310	2,472
Allowance for deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	256	31,685	32,498
Additions (reductions) to Costs and Expenses	21	(31,429)	(813)
Write offs	0	0	0
Balance at End of Period	$ 277	$ 256	$ 31,685