Allowance for Loan Losses and Credit Quality of Loans, Average Recorded Investments on Loans Specifically Evaluated for Impairment and Interest Income Recognized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 21,182	$ 25,672
Interest income recognized	222	206
Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	21,182	25,371
Interest income recognized	222	206
Originated Loans [Member] | Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	5,927	11,324
Interest income recognized	37	57
Originated Loans [Member] | Commercial Loans [Member] | C&I [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	467
Interest income recognized	0
Originated Loans [Member] | Commercial Loans [Member] | CRE [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	4,506
Interest income recognized	32
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment		2,926
Interest income recognized		0
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment		5,995
Interest income recognized		44
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment		173
Interest income recognized		0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment		1,580
Interest income recognized		11
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	954	650
Interest income recognized	5	2
Originated Loans [Member] | Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,374	8,436
Interest income recognized	112	110
Originated Loans [Member] | Consumer Loans [Member] | Dealer Finance [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	184
Interest income recognized	3
Originated Loans [Member] | Consumer Loans [Member] | Direct Lending [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,190	0
Interest income recognized	109	0
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment		5
Interest income recognized		0
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment		8,431
Interest income recognized		110
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	6,881	5,611
Interest income recognized	73	39
Acquired Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	301
Interest income recognized	0	0
Acquired Loans [Member] | Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	301
Interest income recognized	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	301
Interest income recognized	$ 0	$ 0