Investment Securities (State and Municipal Obligations, by State and Economic Sector) (Details)	Jun. 30, 2011
Sector Classification, Texas [Member]
Sector percentage of state and municipal obligation portfolio	10.30%
Sector average life in years	5.6
Sector average credit quality rating	Aa1
Sector Classification, Florida [Member]
Sector percentage of state and municipal obligation portfolio	8.20%
Sector average life in years	5.2
Sector average credit quality rating	Aa3
Sector Classification, Washington [Member]
Sector percentage of state and municipal obligation portfolio	7.00%
Sector average life in years	3.3
Sector average credit quality rating	Aa2
Sector Classification, Arizona [Member]
Sector percentage of state and municipal obligation portfolio	5.10%
Sector average life in years	3.7
Sector average credit quality rating	Aa3
Sector Classification, Illinois [Member]
Sector percentage of state and municipal obligation portfolio	5.10%
Sector average life in years	5.2
Sector average credit quality rating	Aa2
Sector Classification, General obligation [Member]
Sector percentage of state and municipal obligation portfolio	26.00%
Sector average life in years	3.7
Sector average credit quality rating	Aa2
Sector Classification, Housing [Member]
Sector percentage of state and municipal obligation portfolio	18.50%
Sector average life in years	4.9
Sector average credit quality rating	Aa1
Sector Classification, Transportation [Member]
Sector percentage of state and municipal obligation portfolio	16.30%
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	12.80%
Sector average life in years	3.3
Sector average credit quality rating	Aa2
Sector Classification, Refunded [Member]
Sector percentage of state and municipal obligation portfolio	6.70%
Sector average life in years	2.0
Sector average credit quality rating	Aaa