Fair Value - Fair Value and Unpaid Principal Balance of Assets and Liabilities Carried Under Fair Value Option (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Residential loans at fair value	$ 10,172,160	$ 6,710,211
Receivables related to Non-Residual Trusts	45,849	53,975
Assets, Fair Value	10,218,009	6,764,186
Mortgage-backed debt at fair value	708,013	757,286
HMBS related obligations at fair value	8,132,753	5,874,552
Liabilities, Fair Value	8,840,766	6,631,838
Receivables related to Non-Residual Trusts	46,349	54,604
Assets, Unpaid Principal Balance	9,700,706	6,286,286
Mortgage-backed debt related to Non-Residual Trusts	758,121	825,200
HMBS related obligations	7,457,622	5,169,135
Liabilities, Unpaid Principal Balance	8,215,743	5,994,335
Reverse Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Residential loans at fair value	8,137,815	6,047,108
Residential Loans, Unpaid Principal Balance	7,556,982	5,400,876
Residential Loans Related to Non-Residual Trusts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Residential loans at fair value	609,399	646,498
Residential Loans, Unpaid Principal Balance	748,286	814,481
Forward Loans Held for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Residential loans at fair value	1,424,946	16,605
Residential Loans, Unpaid Principal Balance	$ 1,349,089	$ 16,325