FAIR VALUE MEASUREMENTS - Estimated Fair Values for All Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Financial assets
Residential mortgages loans	[1]	$ 3,879,324	$ 4,585,975	[2]
Mortgage servicing rights		500,745	557,813	[2]
Interest rate swaps		26,020	48,114
Financial liabilities
Other secured financing		4,144,623	4,183,311	[2]
Securitized debt of consolidated VIEs		3,693,766	3,347,062	[2]
Interest rate swaps		509,485	420,365
Carrying Value | Level 2
Financial assets
Corporate debt		1,758,082	1,887,182
Corporate debt held for sale, net		44,525	0
Financial liabilities
Repurchase agreements		88,554,170	81,115,874
Other secured financing		4,144,623	4,183,311
Carrying Value | Level 3
Financial assets
Commercial real estate debt and preferred equity, held for investment		722,962	1,296,803
Commercial loans held for sale, net		42,035	42,184
Financial liabilities
Mortgage payable		510,386	511,056
Fair Value | Level 2
Financial assets
Corporate debt		1,742,320	1,863,524
Corporate debt held for sale, net		44,525	0
Financial liabilities
Repurchase agreements		88,554,170	81,115,874
Other secured financing		4,144,491	4,183,805
Fair Value | Level 3
Financial assets
Commercial real estate debt and preferred equity, held for investment		726,687	1,303,487
Commercial loans held for sale, net		42,035	42,184
Financial liabilities
Mortgage payable		$ 519,748	$ 507,770

[1] (4) Includes $101.3 million and $97.5 million of residential mortgage loans held for sale, $42.0 million and $42.2 million of commercial mortgage loans held for sale and $44.5 million and $0 of corporate loans held for sale at March 31, 2019 and December 31, 2018, respectively.

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