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Loans (Recorded Investment by Loan Class in Current and Nonaccrual Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 5,226	$ 7,081
Investment securities, nonaccrual	10,762	8,634
Current	3,516,886	3,163,750
Total Loans	3,532,874	3,179,465	$ 3,114,733
Nonaccrual with no allowance	8,831
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,462	5,897
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	623	1,178
Greater than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	141	6
Commercial Business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	141	361
Investment securities, nonaccrual	2,628	1,177
Current	820,842	569,684
Total Loans	823,611	571,222	573,610
Nonaccrual with no allowance	894
Commercial Business [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	139	361
Commercial Business [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	2
Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans		531
Investment securities, nonaccrual	3,372	3,146
Current	1,200,981	1,104,638
Total Loans	1,204,353	1,108,315	1,037,304
Nonaccrual with no allowance	3,175
Commercial Mortgage [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans		531
Residential Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	424	1,043
Investment securities, nonaccrual	3,305	2,484
Current	580,234	557,190
Total Loans	583,963	560,717	547,839
Nonaccrual with no allowance	3,305
Residential Real Estate Loans [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	389	929
Residential Real Estate Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	35	114
Residential Real Estate Lines [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	288	268
Investment securities, nonaccrual	207	102
Current	90,404	100,678
Total Loans	90,899	101,048	104,545
Nonaccrual with no allowance	207
Residential Real Estate Lines [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	288	231
Residential Real Estate Lines [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans		37
Consumer Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	4,086	4,748
Investment securities, nonaccrual	1,244	1,725
Current	808,015	815,706
Total Loans	813,345	822,179	834,968
Nonaccrual with no allowance	1,244
Consumer Indirect [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	3,520	3,729
Consumer Indirect [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	566	1,019
Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	287	130
Investment securities, nonaccrual	6
Current	16,410	15,854
Total Loans	16,703	15,984	$ 16,467
Nonaccrual with no allowance	6
Other Consumer [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	126	116
Other Consumer [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	20	8
Other Consumer [Member] | Greater than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due Loans	$ 141	$ 6

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