Segments and Geographical Information - Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenue	$ 385,267	$ 278,589	$ 1,052,090	$ 786,671
Gross profit	292,488	209,202	799,030	595,045
Income from operations	98,763	62,079	244,005	180,549
Depreciation and amortization	9,972	6,901	26,715	16,786
Interest and other income (expense), net	3,750	1,463	8,607	1,161
Net income before provision for income taxes and equity in losses of investee	102,513	63,542	252,612	181,710
Operating segments
Segment Reporting Information [Line Items]
Income from operations	168,139	114,408	431,588	327,122
Clear Aligner
Segment Reporting Information [Line Items]
Revenue	341,611	243,668	945,046	706,802
Gross profit	266,285	189,270	737,046	552,663
Income from operations	154,614	102,431	403,264	306,789
Depreciation and amortization	5,643	3,541	15,607	10,163
Scanner
Segment Reporting Information [Line Items]
Revenue	43,656	34,921	107,044	79,869
Gross profit	26,203	19,932	61,984	42,382
Income from operations	13,525	11,977	28,324	20,333
Depreciation and amortization	1,130	761	3,248	2,853
Unallocated corporate expenses
Segment Reporting Information [Line Items]
Income from operations	(69,376)	(52,329)	(187,583)	(146,573)
Depreciation and amortization	$ 3,199	$ 2,599	$ 7,860	$ 3,770

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1,2)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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The net result for the period of deducting operating expenses from operating revenues.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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