Loans Held for Investment and Allowance for Loan Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		$ 195,047	$ 191,522
Provision for credit losses on loans		192,935	47,644
Charge-offs		133,038	25,095
Recoveries		1,193	501
Net charge-offs (recoveries)	$ 74,100	131,845	24,594
Ending balance	264,722	264,722	214,572
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		8,585
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		102,254	96,814
Provision for credit losses on loans		28,850	21,979
Charge-offs		32,940	9,745
Recoveries		770	501
Net charge-offs (recoveries)		32,170	9,244
Ending balance	83,194	83,194	109,549
Commercial \| Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		(15,740)
Energy
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		60,253	34,882
Provision for credit losses on loans		117,963	28,430
Charge-offs		100,098	15,173
Recoveries		423	0
Net charge-offs (recoveries)	62,400	99,675	15,173
Ending balance	102,695	102,695	48,139
Energy \| Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		24,154
Mortgage finance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		2,265	0
Provision for credit losses on loans		299	2,316
Charge-offs		0	0
Recoveries		0	0
Net charge-offs (recoveries)		0	0
Ending balance	4,595	4,595	2,316
Mortgage finance \| Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		2,031
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		30,275	52,595
Provision for credit losses on loans		45,823	2,150
Charge-offs		0	177
Recoveries		0	0
Net charge-offs (recoveries)		0	177
Ending balance	74,238	74,238	54,568
Real Estate \| Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		(1,860)
Additional Qualitative Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		0	7,231
Provision for credit losses on loans		0	(7,231)
Charge-offs		0	0
Recoveries		0	0
Net charge-offs (recoveries)		0	0
Ending balance	$ 0	0	$ 0
Additional Qualitative Reserve \| Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		$ 0

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of increase (decrease) in allowance for credit loss on financing receivable.

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Amount of increase in allowance for credit loss on financing receivable from recovery.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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

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