Loans Acquired - Carrying Value of all Acquired Impaired Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 14,425,260	$ 11,723,171
Loans allowance	68,244	56,694	$ 42,086
Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,795,184	3,292,783
Loans allowance	444	95	$ 418
Loans acquired | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	57,748	15,658
Loans acquired | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,999,658	2,844,472
Loans acquired | Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	475,967	429,605
Loans acquired | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	997,444	566,188
Loans acquired | Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,526,247	1,848,679
Loans acquired | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	737,778	432,653
Loans acquired | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	585,720	430,914
Loans acquired | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 152,058	$ 1,739