Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 11,858,195	$ 10,779,685
Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,734,921	5,074,076
Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	11,644,398	10,438,375
Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,620,803	4,918,570
Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	68,510	165,736
Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	47,672	62,128
Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	144,691	175,064
Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	66,087	93,378
Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	596	376
Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer | Other consumer | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	21,278	51,467
Consumer | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	20,813	50,625
Consumer | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	9	21
Consumer | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	456	821
Consumer | Other consumer | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer | Other consumer | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,114,950	3,818,037
Real estate | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,037,255	3,712,847
Real estate | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	32,769	48,206
Real estate | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	44,567	56,984
Real estate | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Real estate | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Other consumer | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,040,189	2,387,777
Real estate | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,006,371
Real estate | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	12,283
Real estate | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	21,535
Real estate | Other consumer | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Real estate | Other consumer | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Real estate | Construction | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	467,895	637,032
Real estate | Construction | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	440,881	604,796
Real estate | Construction | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	18,011	30,524
Real estate | Construction | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	9,003	1,712
Real estate | Construction | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Construction | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Single family residential | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	606,866	793,228
Real estate | Single family residential | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	590,003	770,954
Real estate | Single family residential | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,475	2,618
Real estate | Single family residential | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	14,029	19,656
Real estate | Single family residential | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	359	0
Real estate | Single family residential | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Other commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,040,189	2,387,777
Real estate | Other commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		2,337,097
Real estate | Other commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		15,064
Real estate | Other commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		35,616
Real estate | Other commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Real estate | Other commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	598,693	1,062,163
Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	562,735	1,012,689
Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	14,894	13,901
Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	21,064	35,573
Commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	596,641	995,587
Commercial | Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	560,791	946,322
Commercial | Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	14,894	13,901
Commercial | Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	20,956	35,364
Commercial | Commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Agricultural | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,052	66,576
Commercial | Agricultural | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	1,944	66,367
Commercial | Agricultural | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Agricultural | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	108	209
Commercial | Agricultural | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Agricultural | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Other
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	142,409
Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		142,409
Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 0