Stock Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 2,416	$ 2,889	$ 8,659	$ 11,710
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	2,316	2,349	7,558	5,690
Vesting of Restricted Stock Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	6	540	1,007	1,620
Stock Awarded to Directors and Officers
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized				4,400
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	94		94
Cost of Sales
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	64	48	164	96
Research and Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	688	567	1,915	1,475
Selling, General, and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense recognized	$ 1,664	$ 2,274	$ 6,580	$ 10,139