Employee and Director Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Postemployment Benefits [Abstract]
Net gain (loss)	$ (80)	$ 288	$ 123
Prior service charge	783	837	1,718
Total accumulated other comprehensive income	$ 703	$ 1,125	$ 1,841