Allowance for Loan and Lease Losses - Credit Quality Indicators by Commercial and Industrial Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	$ 3,159,107	$ 3,033,655
Originated Loans and Leases | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	3,075,265	2,968,737
Originated Loans and Leases | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	34,245	44,334
Originated Loans and Leases | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	49,597	20,584
Total Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	227,436	258,723
Total Acquired Loans | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	223,930	251,103
Total Acquired Loans | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	465	2,265
Total Acquired Loans | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	3,041	5,355
Commercial and industrial | Originated Loans and Leases | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	927,866	932,067
Commercial and industrial | Originated Loans and Leases | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	902,263	919,214
Commercial and industrial | Originated Loans and Leases | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	10,201	6,680
Commercial and industrial | Originated Loans and Leases | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	15,402	6,173
Commercial and industrial | Originated Loans and Leases | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	93,228	108,608
Commercial and industrial | Originated Loans and Leases | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	80,541	100,470
Commercial and industrial | Originated Loans and Leases | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	6,315	8,068
Commercial and industrial | Originated Loans and Leases | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	6,372	70
Commercial and industrial | Total Acquired Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	44,291	50,976
Commercial and industrial | Total Acquired Loans | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	44,008	50,554
Commercial and industrial | Total Acquired Loans | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial and industrial | Total Acquired Loans | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	283	422
Commercial and industrial | Total Acquired Loans | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial and industrial | Total Acquired Loans | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial and industrial | Total Acquired Loans | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial and industrial | Total Acquired Loans | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial real estate | Originated Loans and Leases | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	1,811,348	1,660,782
Commercial real estate | Originated Loans and Leases | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	1,782,283	1,627,713
Commercial real estate | Originated Loans and Leases | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	10,773	19,068
Commercial real estate | Originated Loans and Leases | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	18,292	14,001
Commercial real estate | Originated Loans and Leases | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	147,582	129,712
Commercial real estate | Originated Loans and Leases | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	131,095	119,392
Commercial real estate | Originated Loans and Leases | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	6,956	9,980
Commercial real estate | Originated Loans and Leases | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	9,531	340
Commercial real estate | Originated Loans and Leases | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	179,083	202,486
Commercial real estate | Originated Loans and Leases | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	179,083	201,948
Commercial real estate | Originated Loans and Leases | Construction | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	538
Commercial real estate | Originated Loans and Leases | Construction | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial real estate | Total Acquired Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	181,504	206,020
Commercial real estate | Total Acquired Loans | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	178,281	198,822
Commercial real estate | Total Acquired Loans | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	465	2,265
Commercial real estate | Total Acquired Loans | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	2,758	4,933
Commercial real estate | Total Acquired Loans | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	231	247
Commercial real estate | Total Acquired Loans | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	231	247
Commercial real estate | Total Acquired Loans | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial real estate | Total Acquired Loans | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial real estate | Total Acquired Loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	1,410	1,480
Commercial real estate | Total Acquired Loans | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	1,410	1,480
Commercial real estate | Total Acquired Loans | Construction | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	0	0
Commercial real estate | Total Acquired Loans | Construction | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases, gross	$ 0	$ 0