Loans Held for Investment - Internal Risk Grades (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Internal risk grades of non-covered loans
2020	$ 931,087
2019	1,343,072
2018	1,106,845
2017	620,994
2016	605,861
2015 and Prior	672,622
Financing Receivable, Revolving	700,544
Total loans with credit quality measures	5,981,025
Total loans	7,849,904	$ 7,381,400
Commercial Real Estate
Internal risk grades of non-covered loans
Total loans	3,043,723	3,000,523
Commercial Real Estate | Non-owner occupied
Internal risk grades of non-covered loans
Total loans	1,732,448	1,709,352
Commercial Real Estate | Non-owner occupied | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	8,455
2019	39,658
2018	5,310
2017	12,951
2016	13,452
2015 and Prior	16,990
Financing Receivable, Revolving	402
Total loans with credit quality measures	97,218
Commercial Real Estate | Non-owner occupied | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	123,378
2019	157,843
2018	160,125
2017	124,013
2016	160,255
2015 and Prior	105,776
Financing Receivable, Revolving	22,671
Total loans with credit quality measures	854,061
Commercial Real Estate | Non-owner occupied | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	114,528
2019	133,162
2018	128,832
2017	106,085
2016	144,102
2015 and Prior	66,126
Financing Receivable, Revolving	381
Total loans with credit quality measures	693,216
Commercial Real Estate | Non-owner occupied | Internal Grade 13
Internal risk grades of non-covered loans
2020	3,620
2019	10,571
2018	8,550
2017	13,949
2016	8,153
2015 and Prior	39,591
Total loans with credit quality measures	84,434
Commercial Real Estate | Non-owner occupied | Internal Grade 14
Internal risk grades of non-covered loans
2017	882
2016	222
2015 and Prior	2,415
Total loans with credit quality measures	3,519
Commercial Real Estate | Owner occupied
Internal risk grades of non-covered loans
Total loans	1,311,275	1,291,171
Commercial Real Estate | Owner occupied | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	28,290
2019	30,841
2018	11,075
2017	30,513
2016	23,041
2015 and Prior	46,508
Financing Receivable, Revolving	2
Total loans with credit quality measures	170,270
Commercial Real Estate | Owner occupied | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	104,569
2019	143,052
2018	216,241
2017	84,590
2016	69,401
2015 and Prior	111,861
Financing Receivable, Revolving	29,618
Total loans with credit quality measures	759,332
Commercial Real Estate | Owner occupied | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	75,276
2019	83,909
2018	65,866
2017	29,401
2016	30,419
2015 and Prior	40,902
Financing Receivable, Revolving	9,644
Total loans with credit quality measures	335,417
Commercial Real Estate | Owner occupied | Internal Grade 12 (Special mention)
Internal risk grades of non-covered loans
2015 and Prior	30
Total loans with credit quality measures	30
Commercial Real Estate | Owner occupied | Internal Grade 13
Internal risk grades of non-covered loans
2020	4,418
2019	2,427
2018	3,945
2017	7,614
2016	6,840
2015 and Prior	10,758
Total loans with credit quality measures	36,002
Commercial Real Estate | Owner occupied | Internal Grade 14
Internal risk grades of non-covered loans
2020	552
2018	270
2017	5,591
2016	2,881
2015 and Prior	930
Total loans with credit quality measures	10,224
Commercial | Commercial And Industrial
Internal risk grades of non-covered loans
Total loans	2,736,089	2,025,720
Commercial | Commercial And Industrial | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	22,556
2019	12,880
2018	6,327
2017	5,761
2016	4,310
2015 and Prior	698
Financing Receivable, Revolving	19,218
Total loans with credit quality measures	71,750
Commercial | Commercial And Industrial | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	56,557
2019	107,050
2018	70,933
2017	56,709
2016	23,741
2015 and Prior	16,322
Financing Receivable, Revolving	367,699
Total loans with credit quality measures	699,011
Commercial | Commercial And Industrial | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	66,368
2019	84,275
2018	50,768
2017	20,955
2016	33,751
2015 and Prior	3,035
Financing Receivable, Revolving	183,972
Total loans with credit quality measures	443,124
Commercial | Commercial And Industrial | Internal Grade 12 (Special mention)
Internal risk grades of non-covered loans
2020	6,211
2019	1,337
2017	350
Financing Receivable, Revolving	301
Total loans with credit quality measures	8,199
Commercial | Commercial And Industrial | Internal Grade 13
Internal risk grades of non-covered loans
2020	3,260
2019	3,087
2018	10,155
2017	1,447
2016	5,618
2015 and Prior	666
Financing Receivable, Revolving	11,525
Total loans with credit quality measures	35,758
Commercial | Commercial And Industrial | Internal Grade 14
Internal risk grades of non-covered loans
2020	11,441
2019	10,413
2018	1,851
2017	446
2016	646
2015 and Prior	3,448
Financing Receivable, Revolving	4,014
Total loans with credit quality measures	32,259
Commercial | Mortgage Warehouse Lending
Internal risk grades of non-covered loans
Loans without credit quality measures	774,129
Commercial | Loans Funded Through Paycheck Protection Program
Internal risk grades of non-covered loans
Loans without credit quality measures	671,859
Total loans	671,900
Construction and land development
Internal risk grades of non-covered loans
Total loans	931,899	940,564
Construction and land development | FICO Score, 620 to 720
Internal risk grades of non-covered loans
2020	1,884
2019	82
2018	1,467
Total loans with credit quality measures	3,433
Construction and land development | FICO Score, Greater than 720
Internal risk grades of non-covered loans
2020	6,086
2019	5,330
2018	5,744
Total loans with credit quality measures	17,160
Construction and land development | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	5,880
2019	6,986
2018	22,927
2017	279
2016	1,115
2015 and Prior	311
Financing Receivable, Revolving	2,224
Total loans with credit quality measures	39,722
Construction and land development | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	121,835
2019	184,223
2018	75,290
2017	32,349
2016	7,530
2015 and Prior	4,572
Financing Receivable, Revolving	23,898
Total loans with credit quality measures	449,697
Construction and land development | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	86,018
2019	158,812
2018	137,512
2017	18,524
2016	3,701
2015 and Prior	1,050
Financing Receivable, Revolving	8,398
Total loans with credit quality measures	414,015
Construction and land development | Internal Grade 13
Internal risk grades of non-covered loans
2019	1,112
2017	5,356
Total loans with credit quality measures	6,468
Construction and land development | Internal Grade 14
Internal risk grades of non-covered loans
2019	437
2018	29
2016	769
2015 and Prior	169
Total loans with credit quality measures	1,404
1 - 4 family residential
Internal risk grades of non-covered loans
Total loans	672,843	791,020
1 - 4 family residential | FICO Score, Less than 620
Internal risk grades of non-covered loans
2020	719
2019	882
2018	3,704
2017	229
2016	1,049
2015 and Prior	38,230
Financing Receivable, Revolving	538
Total loans with credit quality measures	45,351
1 - 4 family residential | FICO Score, 620 to 720
Internal risk grades of non-covered loans
2020	8,514
2019	23,071
2018	11,113
2017	9,476
2016	13,609
2015 and Prior	46,358
Financing Receivable, Revolving	1,428
Total loans with credit quality measures	113,569
1 - 4 family residential | FICO Score, Greater than 720
Internal risk grades of non-covered loans
2020	44,434
2019	110,514
2018	94,278
2017	49,710
2016	48,653
2015 and Prior	95,031
Financing Receivable, Revolving	6,342
Total loans with credit quality measures	448,962
1 - 4 family residential | Substandard non-accrual
Internal risk grades of non-covered loans
2017	98
2016	476
2015 and Prior	10,777
Total loans with credit quality measures	11,351
1 - 4 family residential | Other
Internal risk grades of non-covered loans
2020	11,881
2019	18,060
2018	9,735
2017	2,211
2016	1,418
2015 and Prior	9,764
Financing Receivable, Revolving	541
Total loans with credit quality measures	53,610
Consumer
Internal risk grades of non-covered loans
Total loans	42,459	47,046
Consumer | FICO Score, Less than 620
Internal risk grades of non-covered loans
2020	594
2019	1,625
2018	155
2017	155
2016	53
2015 and Prior	90
Financing Receivable, Revolving	356
Total loans with credit quality measures	3,028
Consumer | FICO Score, 620 to 720
Internal risk grades of non-covered loans
2020	2,795
2019	4,283
2018	792
2017	846
2016	156
2015 and Prior	125
Financing Receivable, Revolving	2,347
Total loans with credit quality measures	11,344
Consumer | FICO Score, Greater than 720
Internal risk grades of non-covered loans
2020	7,075
2019	5,027
2018	3,487
2017	410
2016	450
2015 and Prior	66
Financing Receivable, Revolving	4,584
Total loans with credit quality measures	21,099
Consumer | Substandard non-accrual
Internal risk grades of non-covered loans
2017	35
2015 and Prior	23
Financing Receivable, Revolving	250
Total loans with credit quality measures	308
Consumer | Other
Internal risk grades of non-covered loans
2020	3,893
2019	2,123
2018	364
2017	59
2016	50
Financing Receivable, Revolving	191
Total loans with credit quality measures	6,680
Broker-dealer
Internal risk grades of non-covered loans
Loans without credit quality measures	422,891
Total loans	$ 422,891	$ 576,527