Investment Securities (State And Municipal Obligations, By State And Economic Sector) (Details)	3 Months Ended
	Mar. 31, 2013 Y
Sector Classification, Texas [Member]
Investment [Line Items]
% of Portfolio	10.00%
Average Life (in years)	5.5
Average Rating (Moody's)	Aa1
Sector Classification, Florida [Member]
Investment [Line Items]
% of Portfolio	9.50%
Average Life (in years)	5.0
Average Rating (Moody's)	Aa2
Sector Classification, Ohio [Member]
Investment [Line Items]
% of Portfolio	5.80%
Average Life (in years)	5.5
Average Rating (Moody's)	Aa2
Sector Classification, Washington [Member]
Investment [Line Items]
% of Portfolio	5.60%
Average Life (in years)	5.1
Average Rating (Moody's)	Aa2
Sector Classification New York [Member]
Investment [Line Items]
% of Portfolio	5.10%
Average Life (in years)	7.0
Average Rating (Moody's)	Aa2
Sector Classification, General Obligation [Member]
Investment [Line Items]
% of Portfolio	31.90%
Average Life (in years)	5.0
Average Rating (Moody's)	Aa2
Sector Classification, Housing [Member]
Investment [Line Items]
% of Portfolio	17.60%
Average Life (in years)	6.6
Average Rating (Moody's)	Aa1
Sector Classification, Transportation [Member]
Investment [Line Items]
% of Portfolio	13.20%
Average Life (in years)	4.6
Average Rating (Moody's)	Aa3
Sector Classification, Lease [Member]
Investment [Line Items]
% of Portfolio	15.40%
Average Life (in years)	5.0
Average Rating (Moody's)	Aa3
Sector Classification, Limited Tax [Member]
Investment [Line Items]
% of Portfolio	5.10%
Average Life (in years)	5.7
Average Rating (Moody's)	Aa1