Fair Value - Carrying Values and Estimated Fair Values of Financial Assets and Liabilities Required to be Disclosed at Fair Value (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Deferred debt issuance costs	$ 49,168	$ 47,544
Servicing Advance Liabilities [Member]
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Deferred debt issuance costs	500	700
Debt [Member]
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Deferred debt issuance costs	33,900	30,400
Mortgage-backed Debt [Member]
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Deferred debt issuance costs	$ 14,800	$ 16,400