Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 11,740,737	$ 11,723,171
Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,056,187	3,292,783
Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	11,484,631	11,523,787
Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,930,179	3,187,083
Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	78,751	80,394
Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	45,157	51,255
Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	176,789	118,407
Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	80,515	54,097
Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	566	583
Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	336	348
Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
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	11,979	15,658
Consumer | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	11,715	15,380
Consumer | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Consumer | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	264	278
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	2,668,901	2,844,472
Real estate | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,564,477	2,768,761
Real estate | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	41,418	38,839
Real estate | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	62,670	36,524
Real estate | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	336	348
Real estate | 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	404,512	429,605
Real estate | Construction | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	369,267	393,122
Real estate | Construction | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	27,475	27,621
Real estate | Construction | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	7,770	8,862
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	533,917	566,188
Real estate | Single family residential | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	520,159	553,460
Real estate | Single family residential | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	2,049	2,081
Real estate | Single family residential | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	11,373	10,299
Real estate | Single family residential | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	336	348
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	1,730,472	1,848,679
Real estate | Other commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	1,675,051	1,822,179
Real estate | Other commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	11,894	9,137
Real estate | Other commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	43,527	17,363
Real estate | Other commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Real estate | Other commercial | 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	375,307	432,653
Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	353,987	402,942
Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,739	12,416
Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	17,581	17,295
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	374,033	430,914
Commercial | Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	352,779	401,300
Commercial | Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	3,739	12,416
Commercial | Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	17,515	17,198
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	1,274	1,739
Commercial | Agricultural | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Recorded Investment [Line Items]
Loans	1,208	1,642
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	66	97
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