Fair Value - Fair Value and Unpaid Principal Balance of Assets and Liabilities Carried Under Fair Value Option (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, Fair Value	$ 10,184,477,000	$ 6,710,211,000
Receivables related to Non-Residual Trusts	50,890,000	53,975,000
Liabilities, Fair Value	721,080,000	757,286,000
Liabilities, Fair Value	7,805,846,000	5,874,552,000
Reverse Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, Fair Value	0	28,500,000
Reverse Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, Fair Value	7,906,635	6,047,108
Assets, Unpaid Principal Balance	7,087,547	5,400,876
Residential Loans Related to Non-Residual Trusts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, Fair Value	613,627	646,498
Assets, Unpaid Principal Balance	770,917	814,481
Forward Loans Held for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, Fair Value	1,664,215	16,605
Assets, Unpaid Principal Balance	1,652,690	16,325
Receivables related to Non-Residual Trusts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Receivables related to Non-Residual Trusts	50,890	53,975
Assets, Unpaid Principal Balance	51,464	54,604
Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Assets, Fair Value	10,235,367	6,764,186
Assets, Unpaid Principal Balance	9,562,618	6,286,286
Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Liabilities, Fair Value	721,080	757,286
Liabilities, Unpaid Principal Balance	780,116	825,200
HMBS Related Obligations [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Liabilities, Fair Value	7,805,846	5,874,552
Liabilities, Unpaid Principal Balance	6,899,305	5,169,135
Liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Liabilities, Fair Value	8,526,926	6,631,838
Liabilities, Unpaid Principal Balance	$ 7,679,421	$ 5,994,335