Loans (Schedule of Risk Category of Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	$ 2,744,042	[1]	$ 2,154,502	[2]
Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	545,342	[1]	488,058	[2]
Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,211,882	[1]	929,040	[2]
Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	370,694	[1]	337,801	[2]
Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	11,556		9,117		$ 11,048
Loans Acquired with Deteriorated Credit Quality | Branch and Bank Acquisitions
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	481,901
Loans Acquired with Deteriorated Credit Quality | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,038		988		1,656
Loans Acquired with Deteriorated Credit Quality | Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	6,993		6,452		7,688
Loans Acquired with Deteriorated Credit Quality | Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,877		789		$ 706
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,996,743		1,660,271
Pass | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	517,497		462,212
Pass | Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,165,937		894,027
Pass | Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	313,309		304,032
Pass | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0		2,604
Pass | Loans Acquired with Deteriorated Credit Quality | Branch and Bank Acquisitions
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	250,415
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	75,247		53,226
Special Mention | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	7,541		7,901
Special Mention | Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	26,723		18,037
Special Mention | Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	40,983		27,288
Special Mention | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,436		1,647
Special Mention | Loans Acquired with Deteriorated Credit Quality | Branch and Bank Acquisitions
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	14,972
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	55,928		41,402
Substandard | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	20,304		17,945
Substandard | Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	19,222		16,976
Substandard | Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	16,402		6,481
Substandard | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	8,472		3,978
Substandard | Loans Acquired with Deteriorated Credit Quality | Branch and Bank Acquisitions
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	11,521
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0		0
Doubtful | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0		0
Doubtful | Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0		0
Doubtful | Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0		0
Doubtful | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0		0
Doubtful | Loans Acquired with Deteriorated Credit Quality | Branch and Bank Acquisitions
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	0
Total
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	2,127,918		1,754,899
Total | Commercial and Industrial Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	545,342		488,058
Total | Commercial Real Estate Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	1,211,882		929,040
Total | Agricultural Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	370,694		337,801
Total | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	9,908		$ 8,229
Total | Loans Acquired with Deteriorated Credit Quality | Branch and Bank Acquisitions
Financing Receivable, Recorded Investment [Line Items]
Loans, net of deferred income	$ 276,908

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

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