FAIR VALUE MEASUREMENTS - Estimated Fair Values for All Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financial liabilities
Other secured financing	$ 1,805,428	$ 4,455,700	[1]
Carrying Value | Level 1
Financial assets
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	72,580,183	101,740,728
Financial liabilities
Other secured financing	1,805,428	4,455,700
Carrying Value | Level 2
Financial assets
Corporate debt, held for investment	2,150,263	2,144,850
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	72,580,183	101,740,728
Financial liabilities
Other secured financing	1,805,428	4,455,700
Carrying Value | Level 3
Financial assets
Commercial real estate debt and preferred equity, held for investment	1,563,134	1,606,091
Corporate debt, held for investment	2,150,263	2,144,850
Financial liabilities
Mortgage payable	484,762	485,005
Fair Value | Level 1
Financial assets
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	72,580,183	101,740,728
Financial liabilities
Other secured financing	1,805,428	4,455,700
Fair Value | Level 2
Financial assets
Corporate debt, held for investment	1,965,186	2,081,327
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	72,580,183	101,740,728
Financial liabilities
Other secured financing	1,805,428	4,455,700
Fair Value | Level 3
Financial assets
Commercial real estate debt and preferred equity, held for investment	1,589,752	1,619,018
Corporate debt, held for investment	1,969,399	2,081,327
Financial liabilities
Mortgage payable	$ 574,648	$ 515,994

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