Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	$ 6,198,057	$ 5,883,133
Deferred loan origination costs, net	40,300	38,700
Residential loans held for sale	600	0
Loans serviced for unrelated third parties	604,000	616,100
Mortgage servicing rights	900	1,100
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance at January 1	2,346	3,576
New loans	936	390
Adjustment due to change in composition of related parties	(406)	(265)
Repayments	(826)	(1,355)
Balance at December 31	2,050	2,346
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	1,242,701	1,159,089
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	1,543,301	1,430,618
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	1,641,657	1,568,204
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	507,784	528,442
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	2,786,002	2,589,707
Commercial Loans [Member] | Agricultural and Agricultural Real Estate Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans serviced for unrelated third parties	28,500	25,100
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	2,149,441	2,096,646
Residential Real Estate Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	$ 1,262,614	$ 1,196,780