Description of the Business and Basis of Presentation - Deferred Revenue Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred Revenue Disclosure [Abstract]
Deferred revenue, including long-term portion	$ 125,209	$ 111,181
Less: Deferred revenue, long-term portion, included in other liabilities	10,673	10,071
Deferred revenue, short-term portion	$ 114,536	$ 101,110