Changes to Accrued Cease-Use Liability (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Beginning balance	$ 181	$ 972	$ 853	$ 1,983
Change in estimate	0	0	(544)	(830)
Payments	(60)	(58)	(188)	(239)
Ending balance	$ 121	$ 914	$ 121	$ 914