DEBT OBLIGATIONS - Narrative (Details) $ in Thousands	Jun. 30, 2019 USD ($) agreement
Debt Instrument [Line Items]
Face amount of debt	$ 28,783,315
Repurchase Agreements \| Total Repurchase Agreements
Debt Instrument [Line Items]
Face amount of debt	$ 21,481,285
Repurchase Agreements \| Stockholders' Equity, Total \| Counterparty Concentration Risk
Debt Instrument [Line Items]
Number of repurchase agreements, outstanding \| agreement	0

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant