Allowance for Loan and Lease Losses - Credit Quality Indicators by Class of Commercial Real Estate (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Originated Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 3,033,655	$ 2,635,335
Originated Loans and Leases | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,968,737	2,594,534
Originated Loans and Leases | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	44,334	20,485
Originated Loans and Leases | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	20,584	20,316
Originated Loans and Leases | Commercial and industrial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	932,067	847,055
Originated Loans and Leases | Commercial and industrial | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	919,214	836,788
Originated Loans and Leases | Commercial and industrial | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	6,680	7,218
Originated Loans and Leases | Commercial and industrial | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	6,173	3,049
Originated Loans and Leases | Commercial and industrial | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	108,608	118,247
Originated Loans and Leases | Commercial and industrial | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	100,470	117,135
Originated Loans and Leases | Commercial and industrial | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	8,068	755
Originated Loans and Leases | Commercial and industrial | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	70	357
Originated Loans and Leases | Commercial real estate | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,660,782	1,431,690
Originated Loans and Leases | Commercial real estate | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,627,713	1,403,370
Originated Loans and Leases | Commercial real estate | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	19,068	11,939
Originated Loans and Leases | Commercial real estate | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	14,001	16,381
Originated Loans and Leases | Commercial real estate | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	129,712	102,509
Originated Loans and Leases | Commercial real estate | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	119,392	101,407
Originated Loans and Leases | Commercial real estate | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	9,980	573
Originated Loans and Leases | Commercial real estate | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	340	529
Originated Loans and Leases | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	202,486	135,834
Originated Loans and Leases | Commercial real estate | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	201,948	135,834
Originated Loans and Leases | Commercial real estate | Construction | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	538	0
Originated Loans and Leases | Commercial real estate | Construction | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	258,723	330,125
Acquired Loans and Leases | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	251,103	316,458
Acquired Loans and Leases | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,265	526
Acquired Loans and Leases | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	5,355	13,141
Acquired Loans and Leases | Commercial and industrial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	50,976	79,317
Acquired Loans and Leases | Commercial and industrial | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	50,554	77,921
Acquired Loans and Leases | Commercial and industrial | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial and industrial | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	422	1,396
Acquired Loans and Leases | Commercial and industrial | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial and industrial | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial and industrial | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial and industrial | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial real estate | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	206,020	241,605
Acquired Loans and Leases | Commercial real estate | Other | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	198,822	229,334
Acquired Loans and Leases | Commercial real estate | Other | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,265	526
Acquired Loans and Leases | Commercial real estate | Other | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	4,933	11,745
Acquired Loans and Leases | Commercial real estate | Agriculture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	247	267
Acquired Loans and Leases | Commercial real estate | Agriculture | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	247	267
Acquired Loans and Leases | Commercial real estate | Agriculture | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial real estate | Agriculture | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,480	8,936
Acquired Loans and Leases | Commercial real estate | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,480	8,936
Acquired Loans and Leases | Commercial real estate | Construction | Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	0	0
Acquired Loans and Leases | Commercial real estate | Construction | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 0	$ 0