Revenue Recognition - Disaggregated Revenues by Timing of Transfer of Goods or Services (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues									$ 116,640	$ 40,130	$ 22,546
Product Revenue, net
Disaggregation of Revenue [Line Items]
Total revenues	$ 28,375	$ 35,743	$ 27,164	$ 20,362	$ 14,070	$ 7,176	$ 2,265	$ 606	111,644	24,117	0
Collaboration and License Revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 873	$ 1,056	$ 1,260	$ 1,807	$ 1,228	$ 7,001	$ 1,746	$ 6,038	4,996	16,013	$ 22,546
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues									111,644	24,117
Transferred at a point in time | Product Revenue, net
Disaggregation of Revenue [Line Items]
Total revenues									111,644	24,117
Transferred at a point in time | Collaboration and License Revenue
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues									4,996	16,013
Transferred over time | Product Revenue, net
Disaggregation of Revenue [Line Items]
Total revenues									0	0
Transferred over time | Collaboration and License Revenue
Disaggregation of Revenue [Line Items]
Total revenues									$ 4,996	$ 16,013