Loans and Allowance for Loan Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 60,925	$ 34,201
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,893	2,455
Consumer | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	338	296
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,555	2,159
Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	26,506	20,413
Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	2,570	1,269
Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	15,324	11,939
Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	8,612	7,205
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	32,526	11,333
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	31,409	10,049
Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 1,117	$ 1,284