Mortgage Banking Activities - Principal Balance of Mortgage Servicing Rights (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Mortgage loan portfolios serviced for:
Mortgage loan portfolios service	$ 1,100,000	$ 1,100,000
FHLMC
Mortgage loan portfolios serviced for:
Mortgage loan portfolios service	823,109	827,146
FNMA
Mortgage loan portfolios serviced for:
Mortgage loan portfolios service	$ 263,605	$ 283,340