Fair Value - Schedule of Net Fair Value Gains on Reverse Loans and Related HMBS Obligations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Interest income on reverse loans	$ 113,644	$ 113,631	$ 226,946	$ 224,225
Change in fair value of reverse loans	(41,075)	27,744	(111,765)	71,984
Net fair value gains on reverse loans	72,569	141,375	115,181	296,209
Interest expense on HMBS related obligations	(101,290)	(103,368)	(203,726)	(206,622)
Change in fair value of HMBS related obligations	36,593	(30,357)	111,119	(46,729)
Net fair value losses on HMBS related obligations	(64,697)	(133,725)	(92,607)	(253,351)
Net fair value gains on reverse loans and related HMBS obligations	$ 7,872	$ 7,650	$ 22,574	$ 42,858