Employee and Director Benefit Plans - Reconciliation of Accumulated Post-Retirement Benefit Obligation, Included Employee and Director Benefit Plans Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Postemployment Benefits [Abstract]
Accumulated post-retirement benefit obligation as of December 31, 2013	$ 2,853
Service cost	105	55	45
Interest cost	132	82	72
Actuarial loss	544
Benefits paid	(64)	(90)	(67)
Accumulated post-retirement benefit obligation as of December 31, 2014	$ 3,570	$ 2,853