Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 13,127,013	$ 11,723,171
Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,864,516	3,292,783
Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,863,999	11,523,787
Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,727,652	3,187,083
Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	90,248	80,394
Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	56,531	51,255
Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	172,215	118,407
Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	80,009	54,097
Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	551	583
Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	324	348
Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer | Other consumer | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,704	15,658
Consumer | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,532	15,380
Consumer | Other consumer | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer | Other consumer | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	172	278
Consumer | Other consumer | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Consumer | Other consumer | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Real Estate | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,442,152	2,844,472
Real Estate | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,322,663	2,768,761
Real Estate | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	54,994	38,839
Real Estate | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	64,171	36,524
Real Estate | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	324	348
Real Estate | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Real Estate | Construction | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	426,482	429,605
Real Estate | Construction | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	400,925	393,122
Real Estate | Construction | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	17,928	27,621
Real Estate | Construction | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,629	8,862
Real Estate | Construction | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Real Estate | Construction | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Real Estate | Single family residential | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	554,534	566,188
Real Estate | Single family residential | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	539,716	553,460
Real Estate | Single family residential | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,833	2,081
Real Estate | Single family residential | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,661	10,299
Real Estate | Single family residential | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	324	348
Real Estate | Single family residential | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Real Estate | Other commercial | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,461,136	1,848,679
Real Estate | Other commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,382,022	1,822,179
Real Estate | Other commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	35,233	9,137
Real Estate | Other commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	43,881	17,363
Real Estate | Other commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Real Estate | Other commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	412,660	432,653
Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	395,457	402,942
Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,537	12,416
Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	15,666	17,295
Commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Commercial | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	411,577	430,914
Commercial | Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	394,439	401,300
Commercial | Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,537	12,416
Commercial | Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	15,601	17,198
Commercial | Commercial | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Commercial | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Agricultural | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,083	1,739
Commercial | Agricultural | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,018	1,642
Commercial | Agricultural | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Agricultural | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	65	97
Commercial | Agricultural | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Commercial | Agricultural | Risk Rate 8 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0