Loans, Credit Risk Profile Based on Rating Category and Payment Activity and on Performing and Nonperforming Status, Segregated by Class (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		$ 3,118,241	$ 3,122,940
Consumer mortgage loans secured by real estate properties for which formal foreclosure proceedings are in process		4,700	3,700
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		1,611,593	1,619,235
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		$ 1,412,586	1,430,207
Commercial [Member] | Pass [Member] | Minimum [Member]
Financing Receivable, Recorded Investment [Line Items]
Review period for loans		12 months
Commercial [Member] | Pass [Member] | Maximum [Member]
Financing Receivable, Recorded Investment [Line Items]
Review period for loans		18 months
Commercial [Member] | Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		$ 110,798	97,513
Commercial [Member] | OAEM [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		27,296	26,948
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		60,529	63,998
Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		384	569
Commercial [Member] | Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		78,647	76,479
Commercial [Member] | Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		70,672	67,846
Commercial [Member] | Construction [Member] | Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		3,329	3,323
Commercial [Member] | Construction [Member] | OAEM [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		1,060	1,304
Commercial [Member] | Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		3,586	3,828
Commercial [Member] | Construction [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		0	178
Commercial [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		1,191,628	1,188,680
Commercial [Member] | Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		1,048,623	1,053,701
Commercial [Member] | Real Estate [Member] | Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		75,602	65,182
Commercial [Member] | Real Estate [Member] | OAEM [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		22,082	22,401
Commercial [Member] | Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		45,149	47,223
Commercial [Member] | Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		172	173
Commercial [Member] | Equipment Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		2,683	3,042
Commercial [Member] | Equipment Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		2,683	3,005
Commercial [Member] | Equipment Leases [Member] | Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		0	0
Commercial [Member] | Equipment Leases [Member] | OAEM [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		0	37
Commercial [Member] | Equipment Leases [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		0	0
Commercial [Member] | Equipment Leases [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		0	0
Commercial [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		338,635	351,034
Commercial [Member] | Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		290,608	305,655
Commercial [Member] | Other [Member] | Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		31,867	29,008
Commercial [Member] | Other [Member] | OAEM [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		4,154	3,206
Commercial [Member] | Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		11,794	12,947
Commercial [Member] | Other [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		212	218
Residential [Member] | Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		63,893	67,358
Residential [Member] | Construction [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		63,769	66,817
Residential [Member] | Construction [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile	[1]	124	541
Residential [Member] | Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		718,758	709,570
Residential [Member] | Real Estate [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		707,018	695,034
Residential [Member] | Real Estate [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile	[1]	11,740	14,536
Residential [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		99,593	99,356
Residential [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		98,965	98,800
Residential [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile	[1]	628	556
Consumer [Member] | Consumer Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		136,576	137,754
Consumer [Member] | Consumer Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		136,558	137,692
Consumer [Member] | Consumer Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile	[1]	18	62
Consumer [Member] | Consumer Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		487,828	489,667
Consumer [Member] | Consumer Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		487,361	489,019
Consumer [Member] | Consumer Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile	[1]	467	648
Residential and Consumer Portfolio Segments [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		1,506,648	1,503,705
Residential and Consumer Portfolio Segments [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile		1,493,671	1,487,362
Residential and Consumer Portfolio Segments [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loan portfolio based on credit risk profile	[1]	$ 12,977	$ 16,343

[1] A loan is considered nonperforming if it is 90 days or more past due and/or on nonaccrual.