Income Taxes - Provision (Benefit) for Income Taxes Differs from Amounts Computed by Applying Statutory Federal Corporate Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes at statutory rate	$ 3,403	$ 3,440	$ (3,166)
Tax effect of:
Tax-exempt investment income	(21)	(27)	(18)
Change in the beginning of the year balance of the valuation allowance for deferred tax assets allocated to income taxes	(22,427)	(4,277)	580
Stock-based compensation	137	1,133	2,552
State income taxes	525	479	(5)
Other	38	(98)	52
Income tax expense (benefit)	$ (18,345)	$ 650	$ (5)