Mortgage Banking Activities - Principal Balance of Mortgage Servicing Rights (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Mortgage loan portfolios serviced for:
Mortgage loan portfolios service	$ 1,100,000,000	$ 1,100,000,000
FHLMC [Member]
Mortgage loan portfolios serviced for:
Mortgage loan portfolios service	830,295	817,108
FNMA [Member]
Mortgage loan portfolios serviced for:
Mortgage loan portfolios service	$ 291,015	$ 316,142