FAIR VALUES OF FINANCIAL INSTRUMENTS - Summary of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial assets [Abstract]
Residential mortgage loans	$ 11,965,381	$ 13,454,098
Carrying Amount [Member] \| Level 2 [Member]
Financial assets [Abstract]
Residential mortgage loans	1,425	1,864
Lending counterparty investments	5,002	5,002
Financial liabilities [Abstract]
Secured borrowings with initial terms of greater than 120 days		33,073
Unsecured borrowings	98,292	98,191
Fair Value [Member] \| Level 2 [Member]
Financial assets [Abstract]
Residential mortgage loans	1,400	1,900
Lending counterparty investments	5,002	5,002
Financial liabilities [Abstract]
Secured borrowings with initial terms of greater than 120 days		33,100
Unsecured borrowings	76,600	74,100
Interest Rate Swap Agreements [Member] \| Carrying Amount [Member] \| Unsecured Borrowings [Member] \| Level 2 [Member]
Financial liabilities [Abstract]
Interest rate swap agreements	17,834	23,772
Interest Rate Swap Agreements [Member] \| Fair Value [Member] \| Unsecured Borrowings [Member] \| Level 2 [Member]
Financial liabilities [Abstract]
Interest rate swap agreements	$ 17,834	$ 23,772

Investments in FHLB stock and other junior notes receivable with lending counterparties.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
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- Definition

The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

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