Recent Accounting Pronouncements (Impact of ASC 326 in Balance Sheet as January 1, 2020) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	$ 3,012,989		$ 3,091,998				$ 3,081,973
Allowance for Credit Losses	(37,798)	$ (39,995)	(46,859)	$ (46,768)	$ (42,431)	$ (31,931)	(16,278)
Allowance for Credit Losses on Unfunded Loan Commitments						(173)
December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							3,081,973
Allowance for Credit Losses							(16,278)
Allowance for Credit Losses on Unfunded Loan Commitments							0
Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							0
Allowance for Credit Losses						(15,653)
Allowance for Credit Losses on Unfunded Loan Commitments						(173)
Commercial and Industrial Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	510,583		638,773			534,692	589,758
Allowance for Credit Losses	(8,054)	(6,080)	(6,445)	(7,700)	(8,787)		(4,799)
Commercial and Industrial Loans | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							532,501
Commercial and Industrial Loans | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						2,191	(57,257)
Commercial Real Estate Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	1,528,493		1,467,397			1,500,247	1,495,862
Allowance for Credit Losses	(21,392)	(24,220)	(29,878)	(28,382)	(22,369)		(4,692)
Commercial Real Estate Loans | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							1,495,862
Commercial Real Estate Loans | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						4,385
Agricultural Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	349,321		376,186			384,654	384,526
Allowance for Credit Losses	(4,695)	(5,847)	(6,756)	(6,715)	(7,030)		(5,315)
Agricultural Loans | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							384,526
Agricultural Loans | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						128
Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	56,186		55,664			57,257
Allowance for Credit Losses	(203)	(204)	(200)	(206)	(202)		0
Leases | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							57,257
Leases | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						0	57,257
Home Equity Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	217,994		219,348			225,790	225,755
Allowance for Credit Losses	(1,017)	(908)	(996)	(995)	(1,062)		(200)
Home Equity Loans | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							225,755
Home Equity Loans | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						35
Consumer Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	67,150		66,717			69,264	81,217
Allowance for Credit Losses	(483)	(460)	(490)	(492)	(496)		(434)
Consumer Loans | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							69,264
Consumer Loans | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						0	(11,953)
Credit Cards
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	13,856		11,637			11,953
Allowance for Credit Losses	(192)	(181)	(150)	(137)	(125)		0
Credit Cards | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							11,953
Credit Cards | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						0	11,953
Residential Mortgage Loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans	269,406		256,276			305,002	304,855
Allowance for Credit Losses	$ (1,762)	$ (2,095)	$ (1,944)	$ (2,141)	$ (2,360)		(333)
Residential Mortgage Loans | December 31, 2019 After Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans							$ 304,855
Residential Mortgage Loans | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loans						$ 147