SERVICER ADVANCE INVESTMENTS - Summary of Investments in Servicer Advances (Details) - Corporate Joint Venture - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments in and Advances to Affiliates [Line Items]
Amortized Cost Basis	$ 3,924,003,000	$ 5,687,635,000
Carrying Value	$ 4,027,379,000	$ 5,706,593,000
Weighted Average Discount Rate	6.80%	5.60%
Weighted Average Yield	7.30%	5.50%
Weighted Average Life (Years)	5 years 1 month 2 days	4 years 7 months 1 day
Change in Fair Value Recorded in Other Income for Year then Ended	$ 84,418,000	$ (7,768,000)
Asset-backed securities, face amount, collateralized by servicer advances		100,000,000
Asset-backed securities, carrying value, collateralized by servicer advances		$ 100,100,000