Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) segment financial_institution aligner	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | segment	2
Restricted cash	$ 3.5	$ 3.8
Original maturity of highly liquid investments included in Cash and cash equivalents	2 years
Foreign currency net loss	$ 4.0	3.8
Number of financial instutions used | financial_institution	2
Scanners, Warranty period	1 year
No charge period	5 years
Number of optional replacements | aligner	6
Advertising cost	$ 23.4	26.9	$ 26.0
Lease term	9 years
Undistributed earnings of foreign subsidiaries	$ 359.8
Medical device tax expense	$ 6.8
Building
Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful lives	20 years
Software Development
Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful lives	10 years
Capitalized computer software development expenses during period	$ 25.4
Minimum
Significant Accounting Policies [Line Items]
Property plant and equipment estimated useful lives	3 years
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
Property plant and equipment estimated useful lives	10 years
Estimated useful lives of intangibles	15 years
Noncurrent Assets
Significant Accounting Policies [Line Items]
Restricted cash		4.0
Other Noncurrent Assets
Significant Accounting Policies [Line Items]
Restricted cash	$ 3.3	3.6
Prepaid Expenses and Other Current Assets
Significant Accounting Policies [Line Items]
Restricted cash		1.6
Other Current Assets
Significant Accounting Policies [Line Items]
Restricted cash	$ 0.2	$ 0.2