Loans (Residential, Home Equity and Consumer Loans Based on Payment Activity) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 3,012,989	$ 3,091,998		$ 3,081,973
Consumer Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	31,330	33,857
Fiscal Year Before Current Fiscal Year	19,007	16,486
Two Years Before Current Fiscal Year	5,614	8,467
Three Years Before Current Fiscal Year	5,201	2,117
Four Years Before Current Fiscal Year	880	924
Prior	1,960	2,268
Revolving Loans Amortized Cost Basis	3,158	2,598
Total	67,150	66,717	$ 69,264	81,217
Consumer Loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	31,330	33,857
Fiscal Year Before Current Fiscal Year	19,007	16,486
Two Years Before Current Fiscal Year	5,614	8,456
Three Years Before Current Fiscal Year	5,201	2,115
Four Years Before Current Fiscal Year	880	910
Prior	1,944	2,245
Revolving Loans Amortized Cost Basis	3,158	2,563
Total	67,134	66,632
Consumer Loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	11
Three Years Before Current Fiscal Year	0	2
Four Years Before Current Fiscal Year	0	14
Prior	16	23
Revolving Loans Amortized Cost Basis	0	35
Total	16	85
Home Equity Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	28	0
Two Years Before Current Fiscal Year	0	34
Three Years Before Current Fiscal Year	21	46
Four Years Before Current Fiscal Year	45	67
Prior	921	490
Revolving Loans Amortized Cost Basis	216,979	218,711
Total	217,994	219,348	225,790	225,755
Home Equity Loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	28	0
Two Years Before Current Fiscal Year	0	34
Three Years Before Current Fiscal Year	21	46
Four Years Before Current Fiscal Year	45	67
Prior	920	490
Revolving Loans Amortized Cost Basis	216,957	218,440
Total	217,971	219,077
Home Equity Loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	1	0
Revolving Loans Amortized Cost Basis	22	271
Total	23	271
Residential Mortgage Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	76,533	45,945
Fiscal Year Before Current Fiscal Year	41,468	26,536
Two Years Before Current Fiscal Year	15,892	28,050
Three Years Before Current Fiscal Year	18,773	28,764
Four Years Before Current Fiscal Year	21,480	25,155
Prior	95,260	101,826
Revolving Loans Amortized Cost Basis	0	0
Total	269,406	256,276	$ 305,002	$ 304,855
Residential Mortgage Loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	76,533	45,945
Fiscal Year Before Current Fiscal Year	41,468	26,536
Two Years Before Current Fiscal Year	15,892	28,050
Three Years Before Current Fiscal Year	18,773	28,764
Four Years Before Current Fiscal Year	21,480	25,155
Prior	94,721	100,998
Revolving Loans Amortized Cost Basis	0	0
Total	268,867	255,448
Residential Mortgage Loans | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year Before Current Fiscal Year	0	0
Two Years Before Current Fiscal Year	0	0
Three Years Before Current Fiscal Year	0	0
Four Years Before Current Fiscal Year	0	0
Prior	539	828
Revolving Loans Amortized Cost Basis	0	0
Total	$ 539	$ 828