Fair Value - Schedule of Net Fair Value Gains on Reverse Loans and Related HMBS Obligations (Detail) - USD ($) $ in Thousands	1 Months Ended	11 Months Ended	12 Months Ended
	Feb. 09, 2018	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Interest income on reverse loans	$ 47,116	$ 379,215	$ 450,628
Change in fair value of reverse loans	(15,640)	(176,371)	(208,340)
Net fair value gains on reverse loans	31,476	202,844	242,288
Interest expense on HMBS related obligations	(40,427)	(310,721)	(398,241)
Change in fair value of HMBS related obligations	19,527	154,710	198,372
Net fair value losses on HMBS related obligations	(20,900)	(156,011)	(199,869)
Net fair value gains on reverse loans and related HMBS obligations	$ 10,576	$ 46,833	$ 42,419