Fair value of purchased MSRs, their related valuation assumptions and sensitivity to immediate changes in those assumptions (Detail) (Residential Mortgage, Purchased Mortgage Servicing Rights M S R [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Residential Mortgage | Purchased Mortgage Servicing Rights M S R [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Interests Continued To Be Held By Transferor Fair Value	$ 52,531	$ 57,325	$ 52,043
Weighted average life (in years)	12.0	10.9	14.6
Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed	8.30%	9.20%	6.90%
Impact on fair value of 10% adverse change	(2,027)	(2,458)	(1,887)
Impact on fair value of 20% adverse change	(3,624)	(4,401)	(3,303)
Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Discount Rate	11.40%	11.40%	11.40%
Impact on fair value of 10% adverse change	(2,349)	(2,550)	(2,376)
Impact on fair value of 20% adverse change	$ (4,214)	$ (4,552)	$ (4,214)