Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) stage segment financial_institution aligner	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
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)