Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Capitalized software development costs, net of accumulated amortization	$ 735,000	$ 639,000
Amortization of capitalized software development costs	398,000	300,000	$ 230,000
Capital expenditures	710,330	749,348	787,041
New Corporate Headquarters
Property, Plant and Equipment [Line Items]
Capital expenditures			$ 229,000
Building Improvements
Property, Plant and Equipment [Line Items]
Capital expenditures	$ 70,000	$ 30,000