Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of the provision for income taxes [Abstract]
Current income tax expense	$ 18,416,000	$ 20,194,000	$ 19,418,000
Deferred income tax expense (benefit)	115,000	(1,048,000)	582,000
Total income tax expense	18,531,000	19,146,000	20,000,000
Reconciliation of income tax expense at the statutory rate to actual income tax expense [Abstract]
Computed at the statutory rate	22,737,000	21,839,000	22,810,000
Adjustments resulting from [Abstract]
Tax-exempt interest	(1,275,000)	(1,204,000)	(1,126,000)
Housing and new markets credits	(2,692,000)	(1,076,000)	(996,000)
Dividends received deduction	(128,000)	(178,000)	(291,000)
Bank owned life insurance	(549,000)	(503,000)	(791,000)
ESOP dividend deduction	(298,000)	(284,000)	(281,000)
Other, net	736,000	552,000	675,000
Total income tax expense	$ 18,531,000	$ 19,146,000	$ 20,000,000
Reconciliation of income tax expense at the statutory rate to actual income tax expense [Abstract]
Computed at the statutory rate	35.00%	35.00%	35.00%
Adjustment resulting from [Abstract]
Tax-exempt interest	(1.96%)	(1.93%)	(1.73%)
Housing and new markets credits	(4.14%)	(1.72%)	(1.52%)
Dividends received deduction	(0.20%)	(0.29%)	(0.45%)
Bank owned life insurance	(0.84%)	(0.81%)	(1.22%)
ESOP dividend deduction	(0.46%)	(0.46%)	(0.43%)
Other, net	1.13%	0.89%	1.04%
Total	28.53%	30.68%	30.69%
Deferred tax assets [Abstract]
Allowance for loan and lease losses	$ 12,633,000	$ 12,019,000
Interest on nonperforming loans	806,000	1,039,000
Accrued expenses	2,087,000	1,911,000
Allowance for other real estate owned	2,185,000	1,901,000
Other	665,000	1,145,000
Total deferred tax assets	18,376,000	18,015,000
Deferred tax liabilities [Abstract]
Depreciation and amortization	(20,150,000)	(19,181,000)
FHLB stock dividends	(3,460,000)	(3,460,000)
Loan fee income	(552,000)	(744,000)
Mortgage servicing rights	(1,133,000)	(1,039,000)
Capitalized lease obligations	(211,000)	(681,000)
Unrealized gains on AFS securities	(544,000)	(1,231,000)
Limited partnership investments	(650,000)	(395,000)
Other	(596,000)	(776,000)
Total deferred tax liabilities	(27,296,000)	(27,507,000)
Net deferred tax liability	$ (8,920,000)	$ (9,492,000)