Loans (Aging of Past Due Loans) (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total Past Due		$ 31,485		$ 19,974	[1]
Loans Not Past Due		2,986,931		3,075,928	[1]
Total		3,018,416		3,081,973
Total	[1]			3,095,902
Accrued interest included in recorded investment		12,350		13,929
Commercial and Industrial Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		7,444
Loans Not Past Due		502,503
Total		509,947	$ 534,692	589,758
Commercial and Industrial Loans and Leases
Financing Receivable, Past Due [Line Items]
Total Past Due				5,571
Loans Not Past Due				585,832
Total	[1]			591,403
Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		10,523		2,746
Loans Not Past Due		1,478,830		1,497,118
Total		1,489,353	1,500,247	1,495,862
Total	[1]			1,499,864
Agricultural Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		4,130		828
Loans Not Past Due		362,156		390,043
Total		366,286	384,654	384,526
Total	[1]			390,871
Leases
Financing Receivable, Past Due [Line Items]
Total Past Due		0
Loans Not Past Due		55,833
Total		55,833	57,257
Home Equity Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		1,129		1,454
Loans Not Past Due		223,177		225,321
Total		224,306	225,790	225,755
Total	[1]			226,775
Consumer Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		689		592
Loans Not Past Due		67,396		80,837
Total		68,085	69,264	81,217
Total	[1]			81,429
Credit Cards
Financing Receivable, Past Due [Line Items]
Total Past Due		296
Loans Not Past Due		10,760
Total		11,056	11,953
Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		7,274		8,783
Loans Not Past Due		286,276		296,777
Total		293,550	$ 305,002	304,855
Total	[1]			305,560
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		16,854		11,879	[1]
30-59 Days Past Due | Commercial and Industrial Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		1,936
30-59 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Past Due [Line Items]
Total Past Due				4,689
30-59 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		8,238		209
30-59 Days Past Due | Agricultural Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		1,052		499
30-59 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Total Past Due		0
30-59 Days Past Due | Home Equity Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		753		1,121
30-59 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		501		347
30-59 Days Past Due | Credit Cards
Financing Receivable, Past Due [Line Items]
Total Past Due		221
30-59 Days Past Due | Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		4,153		5,014
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		5,344		2,384	[1]
60-89 Days Past Due | Commercial and Industrial Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		319
60-89 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Past Due [Line Items]
Total Past Due				83
60-89 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		733		431
60-89 Days Past Due | Agricultural Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		3,078		0
60-89 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Total Past Due		0
60-89 Days Past Due | Home Equity Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		76		253
60-89 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		51		156
60-89 Days Past Due | Credit Cards
Financing Receivable, Past Due [Line Items]
Total Past Due		21
60-89 Days Past Due | Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		1,066		1,461
Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		9,287		5,711	[1]
Greater Than 89 Days Past Due | Commercial and Industrial Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		5,189
Greater Than 89 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Past Due [Line Items]
Total Past Due				799
Greater Than 89 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		1,552		2,106
Greater Than 89 Days Past Due | Agricultural Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		0		329
Greater Than 89 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Total Past Due		0
Greater Than 89 Days Past Due | Home Equity Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		300		80
Greater Than 89 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		137		89
Greater Than 89 Days Past Due | Credit Cards
Financing Receivable, Past Due [Line Items]
Total Past Due		54
Greater Than 89 Days Past Due | Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Total Past Due		$ 2,055		2,308
Acquired with Deteriorated Credit Quality
Financing Receivable, Past Due [Line Items]
Total Past Due				1,607
Loans Not Past Due				11,191
Total				12,798
Acquired with Deteriorated Credit Quality | Commercial and Industrial Loans and Leases
Financing Receivable, Past Due [Line Items]
Total				1,368
Acquired with Deteriorated Credit Quality | Commercial Real Estate Loans
Financing Receivable, Past Due [Line Items]
Total				7,212
Acquired with Deteriorated Credit Quality | Agricultural Loans
Financing Receivable, Past Due [Line Items]
Total				3,161
Acquired with Deteriorated Credit Quality | Home Equity Loans
Financing Receivable, Past Due [Line Items]
Total				369
Acquired with Deteriorated Credit Quality | Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Total				688
Acquired with Deteriorated Credit Quality | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due				18
Acquired with Deteriorated Credit Quality | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due				0
Acquired with Deteriorated Credit Quality | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due				1,589
Loans Acquired In Current Year | Acquired with Deteriorated Credit Quality
Financing Receivable, Past Due [Line Items]
Total Past Due				1,437
Loans Not Past Due				320,027
Total				321,464
Loans Acquired In Current Year | Acquired with Deteriorated Credit Quality | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due				639
Loans Acquired In Current Year | Acquired with Deteriorated Credit Quality | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due				1
Loans Acquired In Current Year | Acquired with Deteriorated Credit Quality | Greater Than 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due				$ 797

[1] Total recorded investment in loans includes $13,929 in accrued interest.