DEBT AND OTHER OBLIGATIONS - Non-Recourse Funding Obligations (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Outstanding Principal	$ 2,549,691	$ 2,574,691
Carrying Value	2,607,021	2,632,497
Golden Gate Captive Insurance Company
Debt Instrument [Line Items]
Outstanding Principal	1,843,000	1,883,000
Carrying Value	$ 1,843,000	$ 1,883,000
Year-to-Date Weighted-Avg Interest Rate	4.75%	4.75%
Golden Gate II Captive Insurance Company
Debt Instrument [Line Items]
Outstanding Principal	$ 20,600	$ 20,600
Carrying Value	$ 17,717	$ 17,703
Year-to-Date Weighted-Avg Interest Rate	5.60%	4.99%
Golden Gate V Vermont Captive Insurance Company
Debt Instrument [Line Items]
Outstanding Principal	$ 685,000	$ 670,000
Carrying Value	$ 743,981	$ 729,454
Year-to-Date Weighted-Avg Interest Rate	5.12%	5.12%
MONY Life Insurance Company
Debt Instrument [Line Items]
Outstanding Principal	$ 1,091	$ 1,091
Carrying Value	$ 2,323	$ 2,340
Year-to-Date Weighted-Avg Interest Rate	6.19%	6.19%