Collaboration Revenue - Schedule of Revenue Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue recognized in the period from:
Amounts included in the contract liability at the beginning of the period	$ 6,081	$ 8,684	$ 21,909	$ 16,721