Loans Acquired - Nonaccrual Acquired Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 40,505	$ 45,642
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	3,645	4,775
Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	3,317	4,605
Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	22,436	31,727
Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,289	2,242
Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	11,508	13,431
Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	9,639	16,054
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	14,424	9,140
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	11,932	6,980
Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	2,492	2,160
Loans Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	15,981	23,485
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	293	334
Loans Acquired | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	10,686	21,319
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	279	1,767
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	9,053	12,151
Loans Acquired | Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	1,354	7,401
Loans Acquired | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	5,002	1,832
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	4,964	1,748
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans in nonaccrual status	$ 38	$ 84