Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 11,365,895	$ 10,779,685
Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	4,232,434	5,074,076
Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	11,114,152	10,438,375
Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	4,096,419	4,918,570
Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	77,588	165,736
Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	51,985	62,128
Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	173,525	175,064
Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	83,657	93,378
Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	630	376
Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	373	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	31,651	51,467
Consumer | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	30,912	50,625
Consumer | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	10	21
Consumer | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	729	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	3,433,501	3,818,037
Real estate | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,345,324	3,712,847
Real estate | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	32,931	48,206
Real estate | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	54,873	56,984
Real estate | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	373	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	2,240,578	2,387,777
Real estate | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,190,767	2,337,097
Real estate | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	11,345	15,064
Real estate | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	38,466	35,616
Real estate | Other consumer | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Other consumer | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Construction | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	521,321	637,032
Real estate | Construction | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	500,741	604,796
Real estate | Construction | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	19,624	30,524
Real estate | Construction | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	956	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	671,602	793,228
Real estate | Single family residential | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	653,816	770,954
Real estate | Single family residential | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	1,962	2,618
Real estate | Single family residential | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	15,451	19,656
Real estate | Single family residential | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	373	0
Real estate | Single family residential | Risk Rate 8 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Commercial | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	767,282	1,062,163
Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	720,183	1,012,689
Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	19,044	13,901
Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	28,055	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	764,473	995,587
Commercial | Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	717,441	946,322
Commercial | Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	19,044	13,901
Commercial | Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	27,988	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	2,809	66,576
Commercial | Agricultural | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,742	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	67	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