Description of the Business and Basis of Presentation - Changes in Deferred Revenue (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Deferred Revenue Disclosure [Abstract]
Deferred revenue, including long-term portion, beginning balance	$ 90,437	$ 89,400
Additions	487,511	440,220
Revenue recognized during the period	(407,440)	(370,222)
Other adjustments	(2,047)	(3,085)
Deferred revenue, including long-term portion, ending balance	168,461	156,313
Long term deferred revenue	10,475	10,559
Deferred revenue, short-term portion	$ 157,986	$ 145,754