Income Taxes - Components of Income Tax Expense (Benefit) (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Deferred Federal AMT expense (benefit)	$ (147,000)	$ (303,000)	$ (92,000)