Revenue - Summary of Changes in Deferred Revenue Related to Material Right Performance Obligations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue From Contract With Customer [Abstract]
Balance, beginning of period	$ 70,004	$ 57,189	$ 64,651	$ 51,624
Deferral of revenue	6,631	5,643	17,651	14,902
Recognition of unearned revenue	(3,270)	(2,018)	(8,937)	(5,712)
Balance, end of period	$ 73,365	$ 60,814	$ 73,365	$ 60,814