DEBT OBLIGATIONS, NET - Additional Information (Details)								3 Months Ended		12 Months Ended
	Mar. 21, 2017 USD ($) Extension	Feb. 22, 2017	Jan. 13, 2017 USD ($)	Aug. 03, 2016 USD ($) Extension	Oct. 25, 2015	Oct. 31, 2014	Feb. 11, 2014 USD ($) Extension	Mar. 31, 2017 USD ($) servicing_asset counterparty agreement Extension	Mar. 31, 2016 USD ($) agreement	Dec. 31, 2016 USD ($) Extension	Mar. 01, 2017 USD ($)	Jul. 01, 2016 USD ($)	Jun. 28, 2016 USD ($)	Feb. 19, 2016
Committed Loan and Securities Repurchase Facilities
Debt obligations outstanding								$ 1,039,355,000		$ 1,107,185,000
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Contractual payments under current maturities subject to extensions								1,312,542,000
Restricted equity from payment as dividend								899,400,000
Mortgage Loans on Real Estate [Abstract]
Amortization of premiums								$ (226,000)	$ (216,000)
Number of loans transferred for which Company retains control | servicing_asset								2
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Percent of FHLB advances to total debt obligations outstanding								33.70%
Tuebor
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Amount restricted from transfer								$ 324,300,000
Revolving credit facility | One-Month LIBOR
Committed Loan and Securities Repurchase Facilities
Number of extension maturity periods | Extension							4
Length of extension options							12 months
Number of additional extension maturity periods | Extension								2
Length of additional extension maturity periods								1 year
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Basis spread on variable rate (as a percent)							3.50%
Committed amount on credit agreement							$ 168,500,000
Debt borrowings term							3 years
Letters of credit
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Committed amount on credit agreement							$ 25,000,000.0
Term master repurchase agreement
Committed Loan and Securities Repurchase Facilities
Committed amount on master repurchase agreement								$ 400,000,000.0
Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Number of agreements | agreement								5
Committed amount on master repurchase agreement								$ 1,650,000,000		1,650,000,000
Debt obligations outstanding								684,994,000		567,163,000
Total Repurchase Facilities
Committed Loan and Securities Repurchase Facilities
Committed amount on master repurchase agreement								2,050,000,000		2,050,000,000
Debt obligations outstanding								$ 1,039,355,000		$ 1,107,185,000
Total Repurchase Facilities | Deutshe Bank, J.P. Morgan and Wells Fargo
Committed Loan and Securities Repurchase Facilities
Repurchase agreements, number of counterparties | counterparty								9
Excess collateral over amounts borrowed under repurchase agreements								$ 74,100,000
Ratio indebtedness over total equity (as a percent)								5.00%
Haircut on repurchase agreements (as a percent)								36.10%
Uncommitted securities Repurchase Facilities | Minimum
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Advance rates (as a percent)								70.00%
Uncommitted securities Repurchase Facilities | Maximum
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Advance rates (as a percent)								95.00%
Mortgage loan financing
Mortgage Loans on Real Estate [Abstract]
Book value of loans transferred for which Company retains control								$ 56,100,000
Committed Loan Repurchase and Revolving Credit Facilities
Committed Loan and Securities Repurchase Facilities
Number of extension maturity periods | Extension								1
Length of additional extension maturity periods								1 year
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Contractual payments under current maturities subject to extensions								$ 1,000,000,000.0
4/9/2017 | Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Number of extension maturity periods | Extension										2
Committed amount on master repurchase agreement										$ 400,000,000
Length of extension options										364 days
Debt obligations outstanding										$ 100,979,000
4/9/2018 | Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Number of extension maturity periods | Extension								2
Committed amount on master repurchase agreement	$ 300,000,000.0							$ 300,000,000
Length of extension options		1 year
Debt obligations outstanding								$ 151,257,000
Number of additional extension maturity periods | Extension	1							1
Length of additional extension maturity periods	364 days							364 days
4/9/2018 | Committed Loan repurchase facility | Bank
Committed Loan and Securities Repurchase Facilities
Number of additional extension maturity periods | Extension	1
Length of additional extension maturity periods	364 days
10/30/2018 | Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Number of extension maturity periods | Extension								3		3
Committed amount on master repurchase agreement								$ 600,000,000		$ 600,000,000
Length of extension options								12 months	1 year	12 months
Debt obligations outstanding								$ 311,312,000		$ 183,604,000
6/28/2019 | Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Committed amount on master repurchase agreement								100,000,000		100,000,000			$ 100,000,000.0
Debt obligations outstanding								34,369,000		27,132,000
7/1/2018 | Term master repurchase agreement
Committed Loan and Securities Repurchase Facilities
Committed amount on master repurchase agreement								400,000,000		400,000,000		$ 400,000,000.0
Debt obligations outstanding								115,000,000		$ 228,317,000
8/2/2019 | Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Number of extension maturity periods | Extension				1						1
Committed amount on master repurchase agreement				$ 100,000,000.0						$ 100,000,000
Length of extension options				12 months						12 months
Debt obligations outstanding										$ 71,290,000
Number of additional extension maturity periods | Extension				2						2
Length of additional extension maturity periods				6 months						6 months
10/24/2016 | Committed Loan repurchase facility
Committed Loan and Securities Repurchase Facilities
Length of extension options					6 months
Committed amount or master repurchase facility terminated				$ 35,000,000.0
2/28/2022 | Revolving credit facility
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Committed amount on credit agreement											$ 200,000,000.0
Credit and Security Agreement | One-Month LIBOR
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Basis spread on variable rate (as a percent)						1.85%
Credit Agreement and Revolving Credit Facility
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Unamortized debt issuance costs								5,500,000		$ 4,900,000
Mortgage loan financing
Committed Loan and Securities Repurchase Facilities
Number of agreements | agreement									4
Mortgage Loans on Real Estate [Abstract]
Mortgage loan financing								589,200,000		590,100,000
Net unamortized premiums								5,300,000		5,600,000
Amortization of premiums								200,000	$ 200,000
Pledged assets, real estate and lease intangibles, net								$ 749,700,000		$ 757,500,000
Mortgage loan financing | Minimum
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Stated interest rate on debt instrument (as a percent)								4.25%
Mortgage loan financing | Maximum
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Stated interest rate on debt instrument (as a percent)								6.75%
Borrowings from the Federal Home Loan Bank | Tuebor
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Debt borrowings term								7 years		7 years
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Maximum advance limit			$ 2,000,000,000.0
Advance rates of total assets (as a percent)			40.00%
Advance rates of total equity (as a percent)			150.00%
FHLB borrowings outstanding								$ 1,500,000,000		$ 1,700,000,000
Additional committed term financing available from FHLB								$ 524,500,000		$ 338,900,000
Weighted average term								2 years 7 months 6 days		2 years 4 months 24 days
Weighted average interest rate								1.24%		1.12%
Maximum percent of FHLB advances to total assets														40.00%
Borrowings from the Federal Home Loan Bank | Tuebor | Minimum
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Advance rates (as a percent)								57.80%		49.60%
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Stated interest rate on debt instrument (as a percent)								0.57%		0.43%
Borrowings from the Federal Home Loan Bank | Tuebor | Maximum
Borrowing Under Credit Facilties and Debt Issuance Costs [Abstract]
Advance rates (as a percent)								95.20%		95.20%
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Stated interest rate on debt instrument (as a percent)								2.74%		2.74%
Borrowings from the Federal Home Loan Bank | Tuebor | CMBS and U.S. Agency Securities
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Collateral for debt instrument								$ 1,200,000,000		$ 1,400,000,000
Borrowings from the Federal Home Loan Bank | Tuebor | First mortgage commercial real estate loans
Borrowings from Federal Home Loan Bank (FHLB) [Abstract]
Collateral for debt instrument								$ 761,000,000.0		$ 724,000,000.0