Segments and Geographical Information - Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net revenues	$ 490,259	$ 356,482	$ 927,183	$ 666,823
Gross profit	365,582	270,917	692,990	506,542
Income from operations	122,691	83,569	220,883	145,242
Interest income	1,917	1,441	4,093	2,636
Depreciation and amortization	12,632	8,876	24,066	16,743
Other income (expense), net	(7,099)	1,771	(6,922)	2,221
Net income before provision for income taxes and equity in losses of investee	117,509	86,781	218,054	150,099
Operating segments
Segment Reporting Information [Line Items]
Income from operations	207,957	142,711	385,493	263,449
Clear Aligner
Segment Reporting Information [Line Items]
Net revenues	433,241	321,036	818,746	603,435
Gross profit	331,612	250,814	628,588	470,761
Income from operations	190,287	133,916	351,741	248,650
Depreciation and amortization	6,759	5,600	13,143	9,963
Scanner
Segment Reporting Information [Line Items]
Net revenues	57,018	35,446	108,437	63,388
Gross profit	33,970	20,103	64,402	35,781
Income from operations	17,670	8,795	33,752	14,799
Depreciation and amortization	1,169	1,082	2,273	2,119
Unallocated corporate expenses
Segment Reporting Information [Line Items]
Income from operations	(85,266)	(59,142)	(164,610)	(118,207)
Depreciation and amortization	$ 4,704	$ 2,194	$ 8,650	$ 4,661