Loans Held for Investment - Internal Risk Grades (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Internal risk grades of non-covered loans
2020	$ 474,016
2019	1,484,836
2018	1,203,427
2017	756,104
2016	655,723
2015 and Prior	767,491
Financing Receivable, Revolving	842,474
Total loans with credit quality measures	6,184,071
Total loans	7,345,250	$ 7,381,400
Commercial Real Estate
Internal risk grades of non-covered loans
Total loans	3,062,042	3,000,523
Commercial Real Estate | Non-owner occupied
Internal risk grades of non-covered loans
Total loans	1,744,724	1,709,352
Commercial Real Estate | Non-owner occupied | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	2,702
2019	42,015
2018	9,354
2017	14,536
2016	15,164
2015 and Prior	19,926
Financing Receivable, Revolving	402
Total loans with credit quality measures	104,099
Commercial Real Estate | Non-owner occupied | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	45,963
2019	186,755
2018	150,078
2017	149,826
2016	148,241
2015 and Prior	126,033
Financing Receivable, Revolving	25,449
Total loans with credit quality measures	832,345
Commercial Real Estate | Non-owner occupied | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	48,289
2019	117,730
2018	169,739
2017	126,886
2016	174,480
2015 and Prior	82,043
Financing Receivable, Revolving	1,145
Total loans with credit quality measures	720,312
Commercial Real Estate | Non-owner occupied | Internal Grade 13
Internal risk grades of non-covered loans
2019	1,189
2018	1,784
2017	4,317
2016	8,387
2015 and Prior	54,123
Total loans with credit quality measures	69,800
Commercial Real Estate | Non-owner occupied | Internal Grade 14
Internal risk grades of non-covered loans
2019	15,330
2017	882
2015 and Prior	1,956
Total loans with credit quality measures	18,168
Commercial Real Estate | Owner occupied
Internal risk grades of non-covered loans
Total loans	1,317,318	1,291,171
Commercial Real Estate | Owner occupied | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	19,261
2019	35,707
2018	11,362
2017	27,494
2016	23,433
2015 and Prior	48,577
Financing Receivable, Revolving	2
Total loans with credit quality measures	165,836
Commercial Real Estate | Owner occupied | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	73,334
2019	153,997
2018	219,995
2017	91,386
2016	75,445
2015 and Prior	124,679
Financing Receivable, Revolving	31,734
Total loans with credit quality measures	770,570
Commercial Real Estate | Owner occupied | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	6,627
2019	76,220
2018	64,306
2017	92,640
2016	33,586
2015 and Prior	43,919
Financing Receivable, Revolving	15,103
Total loans with credit quality measures	332,401
Commercial Real Estate | Owner occupied | Internal Grade 12 (Special mention)
Internal risk grades of non-covered loans
2015 and Prior	48
Total loans with credit quality measures	48
Commercial Real Estate | Owner occupied | Internal Grade 13
Internal risk grades of non-covered loans
2020	3,466
2019	2,436
2018	3,980
2017	11,661
2016	9,105
2015 and Prior	12,631
Total loans with credit quality measures	43,279
Commercial Real Estate | Owner occupied | Internal Grade 14
Internal risk grades of non-covered loans
2020	555
2018	81
2017	2,528
2016	1,041
2015 and Prior	979
Total loans with credit quality measures	5,184
Commercial | Commercial And Industrial
Internal risk grades of non-covered loans
Collateral maintenance	654,929
Total loans	2,101,968	2,025,720
Commercial | Commercial And Industrial | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	20,004
2019	14,683
2018	7,762
2017	6,239
2016	4,817
2015 and Prior	881
Financing Receivable, Revolving	92,106
Total loans with credit quality measures	146,492
Commercial | Commercial And Industrial | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	36,169
2019	119,001
2018	77,750
2017	58,562
2016	25,450
2015 and Prior	19,585
Financing Receivable, Revolving	374,251
Total loans with credit quality measures	710,768
Commercial | Commercial And Industrial | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	40,361
2019	98,826
2018	64,810
2017	26,805
2016	41,982
2015 and Prior	3,828
Financing Receivable, Revolving	200,425
Total loans with credit quality measures	477,037
Commercial | Commercial And Industrial | Internal Grade 12 (Special mention)
Internal risk grades of non-covered loans
2020	844
2019	1,372
2018	2,028
2017	492
2016	5,246
Financing Receivable, Revolving	13,306
Total loans with credit quality measures	23,288
Commercial | Commercial And Industrial | Internal Grade 13
Internal risk grades of non-covered loans
2020	28
2019	3,411
2018	8,785
2017	2,642
2016	6,596
2015 and Prior	4,396
Financing Receivable, Revolving	16,475
Total loans with credit quality measures	42,333
Commercial | Commercial And Industrial | Internal Grade 14
Internal risk grades of non-covered loans
2020	30,145
2019	2,445
2018	1,506
2017	8,225
2016	231
2015 and Prior	379
Financing Receivable, Revolving	4,190
Total loans with credit quality measures	47,121
Construction and land development
Internal risk grades of non-covered loans
Total loans	955,173	940,564
Construction and land development | FICO Score, 620 to 720
Internal risk grades of non-covered loans
2019	4,394
2018	1,474
Total loans with credit quality measures	5,868
Construction and land development | FICO Score, Greater than 720
Internal risk grades of non-covered loans
2020	3,171
2019	10,617
2018	5,184
Total loans with credit quality measures	18,972
Construction and land development | Other
Internal risk grades of non-covered loans
2020	144
Total loans with credit quality measures	144
Construction and land development | Internal Grade 1-3
Internal risk grades of non-covered loans
2020	4,717
2019	21,250
2018	23,557
2017	282
2016	1,169
2015 and Prior	337
Financing Receivable, Revolving	1,956
Total loans with credit quality measures	53,268
Construction and land development | Internal Grade 4-7
Internal risk grades of non-covered loans
2020	80,147
2019	237,466
2018	106,525
2017	38,310
2016	7,760
2015 and Prior	5,038
Financing Receivable, Revolving	41,525
Total loans with credit quality measures	516,771
Construction and land development | Internal Grade 8-11
Internal risk grades of non-covered loans
2020	24,257
2019	164,164
2018	133,025
2017	22,711
2016	4,431
2015 and Prior	2,119
Financing Receivable, Revolving	6,899
Total loans with credit quality measures	357,606
Construction and land development | Internal Grade 13
Internal risk grades of non-covered loans
2019	1,135
2015 and Prior	7
Total loans with credit quality measures	1,142
Construction and land development | Internal Grade 14
Internal risk grades of non-covered loans
2019	458
2016	768
2015 and Prior	176
Total loans with credit quality measures	1,402
1 - 4 family residential
Internal risk grades of non-covered loans
Total loans	676,630	791,020
1 - 4 family residential | FICO Score, Less than 620
Internal risk grades of non-covered loans
2019	738
2018	3,724
2017	231
2016	1,110
2015 and Prior	40,354
Financing Receivable, Revolving	545
Total loans with credit quality measures	46,702
1 - 4 family residential | FICO Score, 620 to 720
Internal risk grades of non-covered loans
2020	1,252
2019	11,793
2018	15,878
2017	10,850
2016	13,739
2015 and Prior	48,114
Financing Receivable, Revolving	1,585
Total loans with credit quality measures	103,211
1 - 4 family residential | FICO Score, Greater than 720
Internal risk grades of non-covered loans
2020	16,389
2019	84,807
2018	105,533
2017	54,505
2016	50,839
2015 and Prior	106,744
Financing Receivable, Revolving	4,521
Total loans with credit quality measures	423,338
1 - 4 family residential | Substandard non-accrual
Internal risk grades of non-covered loans
2017	101
2016	439
2015 and Prior	10,059
Total loans with credit quality measures	10,599
1 - 4 family residential | Other
Internal risk grades of non-covered loans
2020	8,660
2019	58,480
2018	9,557
2017	2,238
2016	1,466
2015 and Prior	10,152
Financing Receivable, Revolving	2,227
Total loans with credit quality measures	92,780
Consumer
Internal risk grades of non-covered loans
Total loans	43,187	47,046
Consumer | FICO Score, Less than 620
Internal risk grades of non-covered loans
2020	318
2019	1,830
2018	312
2017	193
2016	59
2015 and Prior	100
Financing Receivable, Revolving	373
Total loans with credit quality measures	3,185
Consumer | FICO Score, 620 to 720
Internal risk grades of non-covered loans
2020	2,145
2019	5,082
2018	971
2017	919
2016	183
2015 and Prior	152
Financing Receivable, Revolving	2,686
Total loans with credit quality measures	12,138
Consumer | FICO Score, Greater than 720
Internal risk grades of non-covered loans
2020	2,722
2019	8,327
2018	3,694
2017	542
2016	500
2015 and Prior	131
Financing Receivable, Revolving	5,062
Total loans with credit quality measures	20,978
Consumer | Substandard non-accrual
Internal risk grades of non-covered loans
2017	35
2015 and Prior	25
Financing Receivable, Revolving	250
Total loans with credit quality measures	310
Consumer | Other
Internal risk grades of non-covered loans
2020	2,346
2019	3,178
2018	673
2017	66
2016	56
Financing Receivable, Revolving	257
Total loans with credit quality measures	6,576
Broker-dealer
Internal risk grades of non-covered loans
Collateral maintenance	506,250
Total loans	$ 506,250	$ 576,527