Fair Value - Schedule of Net Fair Value Gains on Reverse Loans and Related HMBS Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Interest income on reverse loans	$ 450,008	$ 435,585	$ 398,925
Change in fair value of reverse loans	(111,687)	(232,993)	35,272
Net fair value gains on reverse loans	338,321	202,592	434,197
Interest expense on HMBS related obligations	(412,090)	(403,817)	(372,346)
Change in fair value of HMBS related obligations	132,791	299,490	48,121
Net fair value gains (losses) on HMBS related obligations	(279,299)	(104,327)	(324,225)
Net fair value gains on reverse loans and related HMBS obligations	$ 59,022	$ 98,265	$ 109,972