Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Securities	Dec. 31, 2015 USD ($) Securities	Dec. 31, 2014 USD ($)
Investments, Debt and Equity Securities [Abstract]
Number of securities holdings | Securities	0	0
Shareholders' equity percentage	10.00%	10.00%
Securities	$ 329,379	$ 312,669
Tax provision related to net realized gains	352	233	$ 150
Proceeds from sale of trading securities	540	2,129	248
Net realized (losses) gains on trading securities	$ 70	$ (211)	$ 10