Income Taxes - Reconciliation of Income Tax Computed at Federal Statutory Rate (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Tax (benefit) expense at statutory tax rate	$ 1,214	$ (3,254)	$ (3,844)
State (benefit) taxes, net of federal tax (benefit)	63	(235)	(151)
Permanent differences	(76)	157	70
Federal and state research credits—current year	(1,046)	(722)	(765)
Federal research credits - prior year	(527)	0	0
(Release) accrual of uncertain tax positions	369	101	(21)
Expiration of statutes for uncertain tax positions	(3,452)	0	(953)
Impact of change in federal and state tax rate on revaluing deferred tax assets	(581)	56	110
Change in valuation allowance	0	756	2,331
Acquisition related adjustments	0	0	(485)
Other	80	(77)	(201)
Benefit for income taxes	$ (3,956)	$ (3,218)	$ (3,909)	$ (3,956)