Revenue from Contracts with Customers - Impact of Adoption of Asc 606 on Company's Condensed Consolidated Statement of Operations (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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 18,028	$ 14,156	$ 12,175	$ 11,281	$ 12,510	$ 11,253	$ 8,744	$ 29,478	$ 3,931	$ 3,571	$ 5,004	$ 3,040	$ 55,640	$ 61,985	$ 15,546
Net loss	$ (7,008)	$ (18,880)	$ (9,770)	$ (10,709)	$ (16,210)	$ (11,951)	$ (14,879)	$ 48,325	$ (15,942)	$ (15,977)	$ (16,486)	$ (18,733)	(33,867)	5,285	(67,138)
Product Sales [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													51,410	34,922	8,266
Product Royalty Revenues [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													3,389	5,070	3,646
Contract Revenues [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													841	$ 21,194	$ 2,500
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													55,610
Net loss													(33,897)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Product Sales [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													51,410
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Product Royalty Revenues [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													3,389
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Contract Revenues [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													811
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													30
Net loss													30
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Contract Revenues [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues													$ 30