Summary of Disaggregation of Product Revenues from Contracts with Customers by Major Product Line (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 49,529	$ 36,580	$ 142,090	$ 99,624
Product revenue, percentage change amount	12,986		42,526
Royalty and other revenue, percentage change amount	(37)		(60)
Total revenue, percentage change amount	$ 12,949		$ 42,466
Product revenue, percentage change	35.60%		42.70%
Royalty and other revenue, percentage change	(56.10%)		(55.60%)
Total revenue, percentage change	35.40%		42.60%
Product Revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 49,500	36,514	$ 142,042	99,516
Royalty and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 29	$ 66	$ 48	$ 108