Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Net book value of assets	$ 23.6	$ 24.6
Depreciation expense	33.7	32.1	$ 29.4
Capitalized Software and Web Site Development Costs [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 13.7	$ 13.7	$ 10.2