Income Taxes - Provision (Benefit) for Income Taxes Differs from Amounts Computed by Applying Statutory Federal Corporate Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
(Benefit) provision for income taxes at statutory rate	$ (15,796)	$ (900)	$ 3,403
Tax effect of:
Tax-exempt investment income	(48)	(22)	(21)
Change in the beginning of the period balance of the valuation allowance for deferred tax assets allocated to federal income taxes	(157)	9	(22,427)
Stock-based compensation	64	22	137
State income taxes, net of federal income tax benefit and state valuation allowance	60	142	525
Other items	29	107	38
Income tax expense (benefit)	$ (15,848)	$ (642)	$ (18,345)