Employee Benefit Plans - Schedule of Vesting Activity Relating to Restricted Stock Units Outstanding (Detail) (Restricted Stock Units [Member], USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Balance, RSUs Vested	136,135	93,225	66,800
Vested, Number of RSUs Vested	38,270	42,910	29,205
Settled, Number of RSUs Vested	(19,550)		(2,780)
Balance, RSUs Vested	154,855	136,135	93,225
Vested, Fair Value	$ 697	$ 844	$ 734
Settled, Fair Value	$ 360		$ 70