Summary of Restructuring Expenses by Function (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses, Cash	$ 236	$ 388
Total restructuring expenses, Non-cash		145
Total restructuring expenses	236	533
Research and Development [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses, Cash	70	357
Total restructuring expenses, Non-cash		145
Total restructuring expenses	70	502
General and Administration [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses, Cash	166	31
Total restructuring expenses	$ 166	$ 31