Loans Held for Investment - Allowance (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Changes in the allowance for loan losses
Balance, beginning of the year	$ 106,739	$ 58,809	$ 61,136	$ 59,486
Provision for (reversal of) credit losses	66,026	(672)	100,575	279
Loans charged off	(17,185)	(3,311)	(19,220)	(5,611)
Recoveries on charged off loans	803	351	1,330	1,023
Balance, end of the year	156,383	55,177	156,383	55,177
ASU 2016-13
Changes in the allowance for loan losses
Balance, beginning of the year			73,700
ASU 2016-13 \| Restatement
Changes in the allowance for loan losses
Balance, beginning of the year			12,562
Commercial Real Estate
Changes in the allowance for loan losses
Balance, beginning of the year	53,939	26,845	31,595	27,100
Provision for (reversal of) credit losses	56,875	(1,731)	71,350	(1,986)
Loans charged off	(4,274)		(4,488)
Recoveries on charged off loans	11		21
Balance, end of the year	106,551	25,114	106,551	25,114
Commercial Real Estate \| ASU 2016-13 \| Restatement
Changes in the allowance for loan losses
Balance, beginning of the year			8,073
Commercial \| Commercial And Industrial
Changes in the allowance for loan losses
Balance, beginning of the year	38,550	21,268	17,964	21,980
Provision for (reversal of) credit losses	5,176	1,254	23,622	1,712
Loans charged off	(12,544)	(2,430)	(13,984)	(4,248)
Recoveries on charged off loans	681	322	1,068	970
Balance, end of the year	31,863	20,414	31,863	20,414
Commercial \| Commercial And Industrial \| ASU 2016-13 \| Restatement
Changes in the allowance for loan losses
Balance, beginning of the year			3,193
Construction and land development
Changes in the allowance for loan losses
Balance, beginning of the year	6,360	5,908	4,878	6,061
Provision for (reversal of) credit losses	2,031	(1,512)	2,938	(1,665)
Loans charged off			(2)
Recoveries on charged off loans	2		2
Balance, end of the year	8,393	4,396	8,393	4,396
Construction and land development \| ASU 2016-13 \| Restatement
Changes in the allowance for loan losses
Balance, beginning of the year			577
1 - 4 family residential
Changes in the allowance for loan losses
Balance, beginning of the year	6,365	4,331	6,386	3,956
Provision for (reversal of) credit losses	1,199	1,447	1,400	1,836
Loans charged off	(170)	(871)	(373)	(899)
Recoveries on charged off loans	5	17	15	31
Balance, end of the year	7,399	4,924	7,399	4,924
1 - 4 family residential \| ASU 2016-13 \| Restatement
Changes in the allowance for loan losses
Balance, beginning of the year			(29)
Consumer
Changes in the allowance for loan losses
Balance, beginning of the year	1,203	409	265	267
Provision for (reversal of) credit losses	319	(128)	565	458
Loans charged off	(197)	(10)	(373)	(464)
Recoveries on charged off loans	104	12	224	22
Balance, end of the year	1,429	283	1,429	283
Consumer \| ASU 2016-13 \| Restatement
Changes in the allowance for loan losses
Balance, beginning of the year			748
Broker-dealer
Changes in the allowance for loan losses
Balance, beginning of the year	322	48	48	122
Provision for (reversal of) credit losses	426	(2)	700	(76)
Balance, end of the year	$ 748	$ 46	$ 748	$ 46

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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