Reverse Mortgage Interests, Net - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	5 Months Ended	7 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests, net		$ 1,219,000
Unsecuritized HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest earned on HECM loans		206,000	$ 274,000	$ 490,000	$ 344,000
Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		107,000	198,000	547,000
Trust 2018-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		364,000
Trust 2017-1
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized		188,000
Trust 2018-1 and Trust 2018-2
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB securitized			760,000
Trust 2016-2 and Trust 2016-3
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecuritized interests, net			284,000
Reverse Mortgage Interests, Unsecuritized | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans	$ 467,000	1,429,000	2,439,000	4,268,000
Repurchase of HECM loans funded by prior servicer		328,000	512,000	1,018,000
HMBS Obligations | HECM
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repurchase of HECM loans	$ 460,000
Other Interest Securitized and Unsecuritized Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
UPB, Purchase discount						$ 290,000
Receivables From Prior Servicers, Reverse Mortgage Interests
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable		18,000		$ 22,000
Mortgage-backed debt | Participating Interests in HMBS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unamortized premium		$ 58,000	$ 58,000			$ 58,000