Revenue - Summary of Unbilled Accounts Receivable and Deferred Revenue (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Unbilled accounts receivable – current	$ 20,507		$ 23,296
Unbilled accounts receivable – noncurrent	8,320		4,122
Deferred revenue – current	60,547	$ 55,738	55,738
Deferred revenue – noncurrent	$ 290		$ 565