Restructuring and Severance (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring And Related Activities [Abstract]
Restructuring and Severance Beginning Balance			$ 237	$ 633
Restructuring expense incurred for the period	$ (49)	$ 160	(49)	3,100
Payments and non-cash item adjustment			$ (188)	(3,246)
Restructuring and Severance Ending Balance		$ 487		$ 487