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
	Mar. 31, 2012	Mar. 31, 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	$ 54,441	$ 62,903	$ 52,043
Weighted average life (in years)	13.7	12.0	14.6
Servicing Assets And Servicing Liabilities At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed	7.30%	8.30%	6.90%
Impact on fair value of 10% adverse change	(1,958)	(2,577)	(1,887)
Impact on fair value of 20% adverse change	(3,474)	(4,642)	(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	(2,405)	(2,821)	(2,376)
Impact on fair value of 20% adverse change	$ (4,305)	$ (5,077)	$ (4,214)