Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 6,751,199	$ 5,139,645
Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,493,493	1,194,646
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	121,757	79,689
Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	612,219	418,703
Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,562,691	1,953,062
Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	962,765	739,169
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	514,021	418,525
Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	86,935	77,479
Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans	2,527	311
Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	394,791	258,061
Commercial Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	5,099,464	3,769,920
Commercial Pass | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,418,401	1,117,545
Commercial Pass | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	73,800	30,712
Commercial Pass | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	587,906	398,646
Commercial Pass | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,408,329	1,811,367
Commercial Pass | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	185,725	146,251
Commercial Pass | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	28,554	7,310
Commercial Pass | Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans	2,527	228
Commercial Pass | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	394,222	257,861
Commercial Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	154,573	124,863
Commercial Special Mention | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	51,336	30,919
Commercial Special Mention | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	27,502	25,273
Commercial Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	828	3,490
Commercial Special Mention | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	70,074	60,028
Commercial Special Mention | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,376	5,106
Commercial Special Mention | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	457	47
Commercial Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans	129,218	159,215
Commercial Substandard | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	23,386	46,182
Commercial Substandard | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	20,018	23,704
Commercial Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	981	1,858
Commercial Substandard | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	79,769	80,626
Commercial Substandard | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	4,209	6,046
Commercial Substandard | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	286	516
Commercial Substandard | Finance Leases
Financing Receivable, Recorded Investment [Line Items]
Loans		83
Commercial Substandard | Other commercial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	569	200
Commercial Doubtful
Financing Receivable, Recorded Investment [Line Items]
Loans	2,407
Commercial Doubtful | Commercial and industrial loans
Financing Receivable, Recorded Investment [Line Items]
Loans	370
Commercial Doubtful | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	387
Commercial Doubtful | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	1,536
Commercial Doubtful | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	114
Commercial Loss
Financing Receivable, Recorded Investment [Line Items]
Loans	50
Commercial Loss | Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment [Line Items]
Loans	50
Consumer Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	1,354,790	1,076,417
Consumer Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	22,374	14,636
Consumer Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	2,980	1,034
Consumer Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	759,900	574,054
Consumer Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	482,661	409,237
Consumer Performing | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	86,875	77,456
Consumer Non Performing
Financing Receivable, Recorded Investment [Line Items]
Loans	10,697	9,230
Consumer Non Performing | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	130	73
Consumer Non Performing | Commercial and farmland
Financing Receivable, Recorded Investment [Line Items]
Loans	3	7
Consumer Non Performing | Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	8,441	7,712
Consumer Non Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	2,063	1,415
Consumer Non Performing | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 60	$ 23