DEBT - Other Debt Financing Expenses (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Apr. 03, 2018	Oct. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Credit Facility prepayments	$ 7,200		$ 54,536	$ 12,071	$ 0
Collateral monitoring fees			1,556	2,505	538
Penalty under credit facility		$ 1,250	0	1,250	0
Amortization of debt issuance costs related to unfunded debt			756	1,190	1,502
Unused line fees			481	893	4,095
Amortization of prepaid agent fees and other			1,002	452	237
Total debt financing expenses			58,331	18,361	6,372
Funded Debt | Write Off DDIC, Prepayment
Debt Instrument [Line Items]
Credit Facility prepayments			7,169	12,071	0
Funded Debt | Write Off DDIC, Pay-off
Debt Instrument [Line Items]
Credit Facility prepayments			44,603	0	0
Unfunded Portion | Principal Prepayments
Debt Instrument [Line Items]
Credit Facility prepayments			$ 2,764	$ 0	$ 0