Summary of Restructuring Expenses by Function (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses, Cash	$ 13	$ 995	$ 2,773	$ 1,919
Total restructuring expenses, Non-cash		269		504
Total restructuring expenses	13	1,264	2,773	2,423
Research and Development [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses, Cash	10	628	184	1,448
Total restructuring expenses, Non-cash		143		336
Total restructuring expenses	10	771	184	1,784
Selling, General and Administrative [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses, Cash	3	367	2,589	471
Total restructuring expenses, Non-cash		126		168
Total restructuring expenses	$ 3	$ 493	$ 2,589	$ 639