SECURED FINANCING - Summary of Gross Amounts, Amounts Offset and Net Amounts of Repurchase Agreement and Reverse Repurchase Agreement (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Reverse Repurchase Agreements
Gross amounts	$ 300,000	$ 250,000
Amounts offset	(300,000)	(250,000)
Netted amounts	0	0
Repurchase Agreements
Gross amounts	61,502,477	65,075,239
Amounts offset	(300,000)	(250,000)
Netted amounts	$ 61,202,477	$ 64,825,239	[1]

[1] Derived from the audited consolidated financial statements at December 31, 2020.