Loans Held for Investment and Allowance for Loan Losses (Allowance Roll Forward) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 124,058	$ 105,217	$ 109,015	$ 110,162
Recoveries of loans previously charged off	3,306	5,330	9,857	12,173
Loans charged off	(32,822)	(45,257)	(93,916)	(135,958)
Provision for loan losses	39,102	39,582	108,688	118,495
Allowance for loan losses at end of period	$ 133,644	$ 104,872	$ 133,644	$ 104,872

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

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- Definition

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

+ References

No definition available.

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- Definition

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

+ References

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-Publisher FASB
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- Definition

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.

+ References

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- Definition

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

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