Summary of Key Economic Assumptions and Sensitivity of Current Fair Value of MSRs (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
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]
Fair value amount of MSRs	$ 5,622		$ 4,638		$ 4,279
Weighted average life (in years)	6 years 1 month 6 days		4 years 9 months 18 days
Prepayment speeds (constant prepayment rate)	11.90%	[1]	15.90%	[1]
10% adverse change	(220)		(230)
20% adverse change	(426)		(442)
Discount rate	10.50%		10.50%
10% adverse change	(220)		(158)
20% adverse change	$ (424)		$ (306)

[1] Represents the weighted average prepayment rate for the life of the MSR asset.