Loans Acquired - Carrying Value of all Acquired Impaired Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,723,171	$ 10,779,685
Loans allowance	56,694	42,086	$ 37,240
Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,292,783	5,074,076
Loans allowance	95	418	$ 954
Loans acquired | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,658	51,467
Loans acquired | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,844,472	3,818,037
Loans acquired | Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	429,605	637,032
Loans acquired | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	566,188	793,228
Loans acquired | Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,848,679	2,387,777
Loans acquired | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	432,653	1,062,163
Loans acquired | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	430,914	995,587
Loans acquired | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,739	66,576
Loans acquired | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 0	$ 142,409