Loans Held for Investment and Allowance for Loan Losses (Details 3) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 191,522	$ 184,655
Provision for loan losses	77,794	84,637
Charge-offs	77,639	80,778
Recoveries	3,370	3,008
Net charge-offs (recoveries)	74,269	77,770
Ending balance	195,047	191,522
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	60,424	8,310
Loans collectively evaluated for impairment	134,623	183,212
Period end loans allocated to:
Loans individually evaluated for impairment	225,384	87,340
Loans collectively evaluated for impairment	24,511,258	22,589,184
Gross loans held for investment	24,736,642	22,676,524
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	129,442	118,806
Provision for loan losses	106,345	87,860
Charge-offs	76,958	79,692
Recoveries	3,290	2,468
Net charge-offs (recoveries)	73,668	77,224
Ending balance	162,119	129,442
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	59,832	8,252
Loans collectively evaluated for impairment	102,287	121,190
Period end loans allocated to:
Loans individually evaluated for impairment	213,460	78,428
Loans collectively evaluated for impairment	10,017,368	10,294,860
Gross loans held for investment	10,230,828	10,373,288
Mortgage Finance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0
Provision for loan losses	2,265	0
Charge-offs	0	0
Recoveries	0	0
Net charge-offs (recoveries)	0	0
Ending balance	2,265	0
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	2,265	0
Period end loans allocated to:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	8,169,849	5,877,524
Gross loans held for investment	8,169,849	5,877,524
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	19,242	19,273
Provision for loan losses	(4,469)	(31)
Charge-offs	0	0
Recoveries	0	0
Net charge-offs (recoveries)	0	0
Ending balance	14,773	19,242
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	14,773	19,242
Period end loans allocated to:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	2,563,339	2,120,966
Gross loans held for investment	2,563,339	2,120,966
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	33,353	34,287
Provision for loan losses	(17,189)	(1,003)
Charge-offs	662	0
Recoveries	0	69
Net charge-offs (recoveries)	662	(69)
Ending balance	15,502	33,353
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	549	48
Loans collectively evaluated for impairment	14,953	33,305
Period end loans allocated to:
Loans individually evaluated for impairment	11,700	8,857
Loans collectively evaluated for impairment	3,433,001	3,920,260
Gross loans held for investment	3,444,701	3,929,117
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	425	357
Provision for loan losses	(441)	397
Charge-offs	0	767
Recoveries	69	438
Net charge-offs (recoveries)	(69)	329
Ending balance	53	425
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	7	10
Loans collectively evaluated for impairment	46	415
Period end loans allocated to:
Loans individually evaluated for impairment	34	55
Loans collectively evaluated for impairment	71,429	63,383
Gross loans held for investment	71,463	63,438
Equipment Leases
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,829	3,542
Provision for loan losses	(1,486)	(1,427)
Charge-offs	19	319
Recoveries	11	33
Net charge-offs (recoveries)	8	286
Ending balance	335	1,829
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	36	0
Loans collectively evaluated for impairment	299	1,829
Period end loans allocated to:
Loans individually evaluated for impairment	190	0
Loans collectively evaluated for impairment	256,272	312,191
Gross loans held for investment	256,462	312,191
Additional Qualitative Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	7,231	8,390
Provision for loan losses	(7,231)	(1,159)
Charge-offs	0	0
Recoveries	0	0
Net charge-offs (recoveries)	0	0
Ending balance	0	7,231
Period end allowance for loan losses allocated to:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	0	7,231
Period end loans allocated to:
Loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	0	0
Gross loans held for investment	$ 0	$ 0

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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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