Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of the provision for income taxes [Abstract]
Current income tax expense	$ 18,417	$ 18,416	$ 20,194
Deferred income tax expense (benefit)	701	115	(1,048)
Total income tax expense	19,118	18,531	19,146
Reconciliation of income tax expense at the statutory rate to actual income tax expense [Abstract]
Computed at the statutory rate	23,262	22,737	21,839
Adjustments resulting from [Abstract]
Tax-exempt interest	(1,289)	(1,275)	(1,204)
Housing and new markets credits	(2,680)	(2,692)	(1,076)
Dividends received deduction	(136)	(128)	(178)
Bank owned life insurance	(518)	(549)	(503)
ESOP dividend deduction	(313)	(298)	(284)
Other, net	792	736	552
Total income tax expense	$ 19,118	$ 18,531	$ 19,146
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	(1.94%)	(1.96%)	(1.93%)
Housing and new markets credits	(4.03%)	(4.14%)	(1.72%)
Dividends received deduction	(0.20%)	(0.20%)	(0.29%)
Bank owned life insurance	(0.78%)	(0.84%)	(0.81%)
ESOP dividend deduction	(0.47%)	(0.46%)	(0.46%)
Other, net	1.18%	1.13%	0.89%
Total	28.76%	28.53%	30.68%
Deferred tax assets [Abstract]
Allowance for loan and lease losses	$ 12,577	$ 12,633
Interest on nonperforming loans	806	806
Accrued expenses	1,883	2,087
Allowance for other real estate owned	1,898	2,185
Unrealized losses on available-for-sale securities	1,241	0
Other	282	665
Total deferred tax assets	18,687	18,376
Deferred tax liabilities [Abstract]
Depreciation and amortization	(20,287)	(20,150)
FHLB stock dividends	(3,460)	(3,460)
Loan fee income	(536)	(552)
Mortgage servicing rights	(1,202)	(1,133)
Capitalized lease obligations	(65)	(211)
Unrealized gains on AFS securities	0	(544)
Limited partnership investments	(411)	(650)
Other	(562)	(596)
Total deferred tax liabilities	(26,523)	(27,296)
Net deferred tax liability	$ (7,836)	$ (8,920)