Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,723,171	$ 10,779,685
Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,523,787	10,438,375
Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	80,394	165,736
Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	118,407	175,064
Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	583	376
Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	134
Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,292,783	5,074,076
Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,187,083	4,918,570
Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	51,255	62,128
Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	54,097	93,378
Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	348	0
Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Consumer | Other consumer | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,658	51,467
Consumer | Other consumer | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,380	50,625
Consumer | Other consumer | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	21
Consumer | Other consumer | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	278	821
Consumer | Other consumer | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Consumer | Other consumer | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Real Estate | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,844,472	3,818,037
Real Estate | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,768,761	3,712,847
Real Estate | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	38,839	48,206
Real Estate | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	36,524	56,984
Real Estate | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	348	0
Real Estate | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Real Estate | Construction | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	429,605	637,032
Real Estate | Construction | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	393,122	604,796
Real Estate | Construction | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	27,621	30,524
Real Estate | Construction | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,862	1,712
Real Estate | Construction | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Real Estate | Construction | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Real Estate | Single family residential | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	566,188	793,228
Real Estate | Single family residential | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	553,460	770,954
Real Estate | Single family residential | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,081	2,618
Real Estate | Single family residential | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	10,299	19,656
Real Estate | Single family residential | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	348	0
Real Estate | Single family residential | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Real Estate | Other commercial | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,848,679	2,387,777
Real Estate | Other commercial | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,822,179	2,337,097
Real Estate | Other commercial | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,137	15,064
Real Estate | Other commercial | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,363	35,616
Real Estate | Other commercial | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Real Estate | Other commercial | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	432,653	1,062,163
Commercial | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	402,942	1,012,689
Commercial | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,416	13,901
Commercial | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,295	35,573
Commercial | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Commercial | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	430,914	995,587
Commercial | Commercial | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	401,300	946,322
Commercial | Commercial | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,416	13,901
Commercial | Commercial | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,198	35,364
Commercial | Commercial | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Commercial | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Agricultural | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,739	66,576
Commercial | Agricultural | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,642	66,367
Commercial | Agricultural | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Agricultural | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	97	209
Commercial | Agricultural | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Commercial | Agricultural | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Other | Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 0	142,409
Other | Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		142,409
Other | Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		0
Other | Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		0
Other | Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		0
Other | Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 0