SECURED FINANCING - Summary of Gross Amounts, Amounts Offset and Net Amounts of Repurchase Agreement and Reverse Repurchase Agreement (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Reverse Repurchase Agreements
Gross amounts	$ 1,000,000	$ 100,000
Amounts offset	(1,000,000)	(100,000)
Netted amounts	0	0
Repurchase Agreements
Gross amounts	73,580,183	101,840,728
Amounts offset	(1,000,000)	(100,000)
Netted amounts	$ 72,580,183	$ 101,740,728	[1]

[1] Derived from the audited consolidated financial statements at December 31, 2019.