Investment Securities (State and Municipal Obligations, by State and Economic Sector) (Details)	Sep. 30, 2011
Sector Classification, Texas [Member]
Sector percentage of state and municipal obligation portfolio	11.20%
Sector average life in years	5.5
Sector average credit quality rating	Aa1
Sector Classification, Florida [Member]
Sector percentage of state and municipal obligation portfolio	8.40%
Sector average life in years	5.0
Sector average credit quality rating	Aa3
Sector Classification, Washington [Member]
Sector percentage of state and municipal obligation portfolio	7.40%
Sector average life in years	3.3
Sector average credit quality rating	Aa2
Sector Classification, Illinois [Member]
Sector percentage of state and municipal obligation portfolio	5.20%
Sector average life in years	5.3
Sector average credit quality rating	Aa2
Sector Classification, Ohio [Member]
Sector percentage of state and municipal obligation portfolio	4.80%
Sector average life in years	5.3
Sector average credit quality rating	Aa1
Sector Classification, General obligation [Member]
Sector percentage of state and municipal obligation portfolio	26.30%
Sector average life in years	4.0
Sector average credit quality rating	Aa2
Sector Classification, Housing [Member]
Sector percentage of state and municipal obligation portfolio	19.50%
Sector average life in years	4.5
Sector average credit quality rating	Aa1
Sector Classification, Transportation [Member]
Sector percentage of state and municipal obligation portfolio	15.90%
Sector average life in years	4.0
Sector average credit quality rating	Aa3
Sector Classification, Lease [Member]
Sector percentage of state and municipal obligation portfolio	13.10%
Sector average life in years	3.8
Sector average credit quality rating	Aa3
Sector Classification, Limited Tax [Member]
Sector percentage of state and municipal obligation portfolio	5.80%
Sector average life in years	5.3
Sector average credit quality rating	Aa1