Description of the Business and Basis of Presentation - Changes in Deferred Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Deferred Revenue Disclosure [Abstract]
Deferred revenue, including long-term portion, beginning balance	$ 90,437	$ 89,400
Additions	197,227	173,477
Revenue recognized during the period	(137,509)	(117,690)
Other adjustments	(744)	(1,451)
Deferred revenue, including long-term portion, ending balance	149,411	143,736
Long term deferred revenue	10,606	10,494
Deferred revenue	$ 138,805	$ 133,242	$ 79,554