Loans Receivable and Allowance for Credit Losses (Composition of Loans Held-for-Investment- Narrative) (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Accrued interest receivable	$ 108,100,000	$ 108,100,000	$ 121,800,000
Interest income related to nonaccrual loans reversed	1,200,000	2,600,000
Interest income recognized on nonaccrual loans	18,000	29,000
Loans receivable pledged to secure borrowings and to provide additional borrowing capacity from the FRB and the FHLB	27,059,316,000	27,059,316,000	$ 22,431,092,000
HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Converted to term loan	59,800,000	118,200,000
Commercial and industrial (“C&I”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Converted to term loan	250,000	250,000
Commercial real estate (“CRE”)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Converted to term loan	$ 0	$ 0

Financing Receivable, Amount Converted to term loans

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- Definition

Net Reduction to Interest Income

+ References

No definition available.

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- Definition

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+ References

No definition available.

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- Definition

Amount, before allowance for credit loss, of accrued interest on financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL120267963-210447

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- Definition

Amount of interest income on financing receivable on nonaccrual status.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

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- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
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-Publisher FASB
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-Section 50
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