Income Taxes - Provision (Benefit) for Income Taxes Differs from Amounts Computed by Applying Statutory Federal Corporate Tax Rate (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes at statutory rate	$ 1,172	$ (115)	$ 1,206	$ (13,758)
Tax effect of:
Tax-exempt investment income	(20)	(10)	(54)	(30)
Change in the beginning of the period balance of the valuation allowance for deferred tax assets allocated to federal income taxes	(1)	(6)	(1)	51
Stock option expirations		12	229	29
State income taxes, net of federal income tax benefit and state valuation allowance	206	116	212	110
Other	(4)	9	30	27
Income tax expense (benefit)	$ 1,353	$ 6	$ 1,622	$ (13,571)