Borrowed Funds - Summary of Federal Home Loan Bank Advances and Securities Sold Under Agreements to Repurchase (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
FHLB Advances [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Average balance	$ 219,847	$ 219,102
Maximum amount outstanding at any month end	305,238	282,500
Average interest rate for the year	1.14%	1.82%
Reverse Repurchase Agreements [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Average balance	64,223	69,621
Maximum amount outstanding at any month end	68,856	73,067
Average interest rate for the year	0.12%	0.18%
Amortized cost of collateral, Mortgage-backed securities	70,449	78,474
Estimated fair value of collateral, Mortgage-backed securities	$ 70,954	$ 78,512