Retirement Plans - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Employee service period under ESOP	1 year
Deferred compensation obligations	$ 7,484,000		$ 7,408,000
Earnings credits on deferred balances included in noninterest expense	149,000	152,000
401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum age for employees	21 years
Minimum period for employees to participate	90 days
Employee Stock Ownership Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution and paid out as benefits	368,000	195,000
Supplemental Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution and paid out as benefits	219,000	125,000
Supplemental Retirement Plans [Member] | December 31, 2015 [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution and paid out as benefits	$ 1,194,000