SECURED FINANCING - Summary of Gross Amounts, Amounts Offset and Net Amounts of Repurchase Agreement and Reverse Repurchase Agreement (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Reverse Repurchase Agreements
Gross amounts	$ 550,000	$ 650,040
Amounts offset	(550,000)	0
Netted amounts	0	650,040	[1]
Repurchase Agreements
Gross amounts	103,232,104	81,115,874
Amounts offset	(550,000)	0
Netted amounts	$ 102,682,104	$ 81,115,874	[1]

[1] ⁽¹⁾  Derived from the audited consolidated financial statements at December 31, 2018.