Loans and Allowance for Loan Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 61,956	$ 34,201
Consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,898	2,455
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	327	296
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,571	2,159
Real Estate
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	27,635	20,413
Real Estate | Construction
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	2,140	1,269
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	15,648	11,939
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	9,847	7,205
Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	32,423	11,333
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	31,240	10,049
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 1,183	$ 1,284