Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Interest bearing amounts held at other financial institutions	$ 39.8	$ 96.8	$ 39.8	$ 96.8
Dilutive effect of common stock issuable upon exercise of options and nonvested restricted shares	549,819	435,029	616,990	369,781
Anti-dilutive shares	150,739	394,863	150,739	628,698