Allowance for Loan Losses - Summary of Changes in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Allowance for loan losses, beginning of year				$ 20,941				$ 19,197	$ 20,941	$ 19,197	$ 16,574
Loans charged-off									(1,382)	(1,813)	(2,301)
Recoveries on loans previously charged-off									709	847	774
Net charge-offs									(673)	(966)	(1,527)
Provision charged to expense	400	600	450	600	460	750	750	750	2,050	2,710	4,150
Allowance for loan losses, end of year	$ 22,318				$ 20,941				$ 22,318	$ 20,941	$ 19,197