Loans Acquired - Summary of Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 13,002,952	$ 11,723,171
Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,359,587	3,292,783
Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,761,764	11,523,787
Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,272,024	3,187,083
Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	95,017	80,394
Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	46,796	51,255
Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	146,039	118,407
Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	40,639	54,097
Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	132	583
Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128	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	7,431	15,658
Consumer | Other consumer | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,285	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	146	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	3,001,463	2,844,472
Real Estate | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,922,550	2,768,761
Real Estate | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	45,305	38,839
Real Estate | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	33,480	36,524
Real Estate | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128	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	362,000	429,605
Real Estate | Construction | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	344,075	393,122
Real Estate | Construction | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	17,874	27,621
Real Estate | Construction | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	51	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	504,490	566,188
Real Estate | Single family residential | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	492,826	553,460
Real Estate | Single family residential | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,224	2,081
Real Estate | Single family residential | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,312	10,299
Real Estate | Single family residential | Risk Rate 7 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128	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	2,134,973	1,848,679
Real Estate | Other commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,085,649	1,822,179
Real Estate | Other commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	26,207	9,137
Real Estate | Other commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	23,117	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	350,693	432,653
Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	342,189	402,942
Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,491	12,416
Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,013	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	349,821	430,914
Commercial | Commercial | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	341,385	401,300
Commercial | Commercial | Risk Rate 5 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,491	12,416
Commercial | Commercial | Risk Rate 6 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,945	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	872	1,739
Commercial | Agricultural | Risk Rate 1-4 | Loans acquired, net
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	804	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	68	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