Loans (Schedule of Aging of Recorded Investment in Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	$ 2,725,212	[1]	$ 2,744,042	[2]
Loans Past Due	17,363	[1]	21,364	[2]
Loans Not Past Due	2,707,849	[1]	2,722,678	[2]
Accrued interest included in recorded investment	12,798		12,301
Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	10,472		11,556
Loans Past Due	2,290		2,592
Loans Not Past Due	8,182		8,964
Loans Acquired With Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income			481,901
Loans Past Due			6,382
Loans Not Past Due			475,519
Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	557,660	[1]	545,342	[2]
Loans Past Due	4,716		5,669
Loans Not Past Due	552,944		539,673
Commercial and Industrial Loans and Leases | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	902		1,038
Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	1,215,532	[1]	1,211,882	[2]
Loans Past Due	3,286		4,505
Loans Not Past Due	1,212,246		1,207,377
Commercial Real Estate Loans | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	6,127		6,993
Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	353,606	[1]	370,694	[2]
Loans Past Due	1,252		1,642
Loans Not Past Due	352,354		369,052
Agricultural Loans | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	1,798		1,877
Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	204,626	[1]	209,009	[2]
Loans Past Due	666		656
Loans Not Past Due	203,960		208,353
Home Equity Loans | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	368		365
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	78,356	[1]	77,761	[2]
Loans Past Due	652		1,214
Loans Not Past Due	77,704		76,547
Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	315,432	[1]	329,354	[2]
Loans Past Due	6,791		7,678
Loans Not Past Due	308,641		321,676
Residential Mortgage Loans | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, net of deferred income	1,277		1,283
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	11,343	[1]	12,958	[2]
30-59 Days Past Due | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	0		448
30-59 Days Past Due | Loans Acquired With Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due			2,571
30-59 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	4,447		5,414
30-59 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	896		768
30-59 Days Past Due | Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	16		563
30-59 Days Past Due | Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	546		471
30-59 Days Past Due | Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	216		971
30-59 Days Past Due | Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	5,222		4,771
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	1,024	[1]	3,432	[2]
60-89 Days Past Due | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	68		885
60-89 Days Past Due | Loans Acquired With Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due			1,620
60-89 Days Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	218		183
60-89 Days Past Due | Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	68		705
60-89 Days Past Due | Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	365		805
60-89 Days Past Due | Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	3		125
60-89 Days Past Due | Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	213		94
60-89 Days Past Due | Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	157		1,520
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	4,996	[1]	4,974	[2]
90 Days or More Past Due | Loans Acquired With Deteriorated Credit Quality
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	2,222		1,259
90 Days or More Past Due | Loans Acquired With Deteriorated Credit Quality | Loans Acquired in Current Year
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due			2,191
90 Days or More Past Due | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	51		72
90 Days or More Past Due | Commercial Real Estate Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	2,322		3,032
90 Days or More Past Due | Agricultural Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	871		274
90 Days or More Past Due | Home Equity Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	117		60
90 Days or More Past Due | Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	223		149
90 Days or More Past Due | Residential Mortgage Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans Past Due	$ 1,412		$ 1,387

[1] Total recorded investment in loans includes $12,798 in accrued interest.

[2] Total recorded investment in loans includes $12,301 in accrued interest.