Loans Receivable and Allowance for Credit Losses (Composition of Loans Held-for-Investment- Narrative) (Details)	3 Months Ended
Mar. 31, 2020 USD ($) property_unit	Dec. 31, 2019 USD ($)
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Accrued interest receivable	$ 117,600,000	$ 121,800,000
Interest income related to nonaccrual loans reversed	366,000
Interest income recognized on nonaccrual loans	0
Loans receivable pledged to secure borrowings and to provide additional borrowing capacity from the FRB and the FHLB	23,107,287,000	$ 22,431,092,000
HELOCs
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Converted to term loan	31,300,000
Commercial And Industrial And Commercial Real Estate
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Converted to term loan	$ 0
Consumer lending \| Single-family residential and home equity line of credit
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loan-to-value ratio (or less at origination)	60.00%
Multifamily residential \| Commercial lending \| Minimum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units in multifamily properties used to secure multifamily residential loans \| property_unit	5

Financing Receivable, Accrued Interest, before Allowance for Credit Loss

No definition available.

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- Definition

Financing Receivable, Amount Converted to term loans

+ References

No definition available.

+ Details

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- Definition

Ratio which compares the amount of the borrower’s first mortgage with the appraised value of the property. It is computed as Current Loan Balance ÷ Current Appraised Value

+ References

No definition available.

+ Details

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- Definition

Net Reduction to Interest Income

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Number of Units in the Multifamily Properties Used as Collateral

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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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=119407570&loc=SL82919258-210447

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5086-111524

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- Details

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- Details

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- Details

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- Details

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