Investment Securities (State And Municipal Obligations, By State And Economic Sector) (Details)	Mar. 31, 2012
Sector Classification, Texas [Member]
Investment [Line Items]
% of Portfolio	10.10%
Average Life (in years)	5.3
Average Rating (Moody's)	Aa1
Sector Classification, Florida [Member]
Investment [Line Items]
% of Portfolio	9.10%
Average Life (in years)	4.7
Average Rating (Moody's)	Aa3
Sector Classification, Washington [Member]
Investment [Line Items]
% of Portfolio	6.20%
Average Life (in years)	4.0
Average Rating (Moody's)	Aa2
Sector Classification, Illinois [Member]
Investment [Line Items]
% of Portfolio	4.90%
Average Life (in years)	6.0
Average Rating (Moody's)	Aa3
Sector Classification, Ohio [Member]
Investment [Line Items]
% of Portfolio	4.90%
Average Life (in years)	5.1
Average Rating (Moody's)	Aa2
Sector Classification, General Obligation [Member]
Investment [Line Items]
% of Portfolio	27.50%
Average Life (in years)	4.5
Average Rating (Moody's)	Aa2
Sector Classification, Housing [Member]
Investment [Line Items]
% of Portfolio	20.00%
Average Life (in years)	4.6
Average Rating (Moody's)	Aa1
Sector Classification, Transportation [Member]
Investment [Line Items]
% of Portfolio	14.50%
Average Life (in years)	4.0
Average Rating (Moody's)	Aa3
Sector Classification, Lease [Member]
Investment [Line Items]
% of Portfolio	13.90%
Average Life (in years)	3.7
Average Rating (Moody's)	Aa3
Sector Classification, Limited Tax [Member]
Investment [Line Items]
% of Portfolio	6.40%
Average Life (in years)	5.1
Average Rating (Moody's)	Aa2