Revenue Recognition - Disaggregated Revenues by Timing of Transfer of Goods or Services (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Disaggregated Revenue									$ 40,130	$ 22,546	$ 35,504
Product Revenue, net
Disaggregation of Revenue [Line Items]
Disaggregated Revenue	$ 14,070	$ 7,176	$ 2,265	$ 606					24,117
Collaboration and License Revenue
Disaggregation of Revenue [Line Items]
Disaggregated Revenue	$ 1,228	$ 7,001	$ 1,746	$ 6,038	$ 9,803	$ 3,828	$ 3,787	$ 5,128	16,013	$ 22,546	$ 35,504
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Disaggregated Revenue									24,117
Transferred at a point in time | Product Revenue, net
Disaggregation of Revenue [Line Items]
Disaggregated Revenue									24,117
Transferred over time
Disaggregation of Revenue [Line Items]
Disaggregated Revenue									16,013
Transferred over time | Collaboration and License Revenue
Disaggregation of Revenue [Line Items]
Disaggregated Revenue									$ 16,013