Description of the Business and Basis of Presentation - Changes in Deferred Revenue (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Deferred Revenue Disclosure [Abstract]
Deferred revenue, including long-term portion	$ 161,253	$ 111,181
Long term deferred revenue	10,000	10,071
Deferred revenue, short-term portion	$ 151,253	$ 101,110