Loans (Schedule of Aging of Recorded Investment in Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2018		Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	$ 2,163,545	[1]	$ 2,154,502	[2]
Loans Past Due	11,169	[1]	11,975	[2]
Loans Not Past Due	2,152,376	[1]	2,142,527	[2]
Accrued interest included in recorded investment	9,697		9,483
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	8,819		9,117
Loans Past Due	545		443
Loans Not Past Due	8,274		8,674
Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	483,512	[1]	488,058	[2]
Loans Past Due	1,472		2,479
Loans Not Past Due	482,040		485,579
Commercial and Industrial Loans and Leases | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	790		988
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	950,326	[1]	929,040	[2]
Loans Past Due	3,432		3,556
Loans Not Past Due	946,894		925,484
Commercial Real Estate Loans | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	6,194		6,452
Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	333,988	[1]	337,801	[2]
Loans Past Due	334		295
Loans Not Past Due	333,654		337,506
Agricultural Loans | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	957		789
Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	152,527	[1]	152,757	[2]
Loans Past Due	811		658
Loans Not Past Due	151,716		152,099
Home Equity Loans | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	0		0
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	64,655	[1]	67,647	[2]
Loans Past Due	436		629
Loans Not Past Due	64,219		67,018
Consumer Loans | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	0		0
Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	178,537	[1]	179,199	[2]
Loans Past Due	4,684		4,358
Loans Not Past Due	173,853		174,841
Residential Mortgage Loans | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	878		888
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	6,652	[1]	4,927	[2]
30-59 Days Past Due | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	518		342
30-59 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	659		209
30-59 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	1,195		1,229
30-59 Days Past Due | Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	106		27
30-59 Days Past Due | Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	529		366
30-59 Days Past Due | Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	303		246
30-59 Days Past Due | Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	3,860		2,850
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	459	[1]	4,452	[2]
60-89 Days Past Due | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	0		74
60-89 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	180		1,365
60-89 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	0		1,650
60-89 Days Past Due | Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	0		0
60-89 Days Past Due | Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	94		93
60-89 Days Past Due | Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	62		97
60-89 Days Past Due | Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	123		1,247
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	4,058	[1]	2,596	[2]
90 Days or More Past Due | Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	27		27
90 Days or More Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	633		905
90 Days or More Past Due | Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	2,237		677
90 Days or More Past Due | Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	228		268
90 Days or More Past Due | Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	188		199
90 Days or More Past Due | Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	71		286
90 Days or More Past Due | Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	$ 701		$ 261

[1] Total recorded investment in loans includes $9,697 in accrued interest.

[2] Total recorded investment in loans includes $9,483 in accrued interest.