Investment Securities (State And Municipal Obligations, By State And Economic Sector) (Details)	Dec. 31, 2011
Sector Classification, Texas [Member]
Sector percentage of state and municipal obligation portfolio	11.30%
Sector average life in years	5.2
Average Rating (Moody's)	Aa1
Sector Classification, Florida [Member]
Sector percentage of state and municipal obligation portfolio	8.60%
Sector average life in years	4.7
Average Rating (Moody's)	Aa3
Sector Classification, Washington [Member]
Sector percentage of state and municipal obligation portfolio	6.40%
Sector average life in years	3.9
Average Rating (Moody's)	Aa2
Sector Classification, Ohio [Member]
Sector percentage of state and municipal obligation portfolio	4.80%
Sector average life in years	5.2
Average Rating (Moody's)	Aa2
Sector Classification, Illinois [Member]
Sector percentage of state and municipal obligation portfolio	4.80%
Sector average life in years	5.6
Average Rating (Moody's)	Aa3
Sector Classification, General obligation [Member]
Sector percentage of state and municipal obligation portfolio	24.80%
Sector average life in years	4.3
Average Rating (Moody's)	Aa2
Sector Classification, Housing [Member]
Sector percentage of state and municipal obligation portfolio	20.50%
Sector average life in years	4.6
Average Rating (Moody's)	Aa1
Sector Classification, Transportation [Member]
Sector percentage of state and municipal obligation portfolio	15.80%
Sector average life in years	3.9
Average Rating (Moody's)	Aa3
Sector Classification, Lease [Member]
Sector percentage of state and municipal obligation portfolio	13.40%
Sector average life in years	3.7
Average Rating (Moody's)	Aa3
Sector Classification, Limited Tax [Member]
Sector percentage of state and municipal obligation portfolio	5.90%
Sector average life in years	5.1
Average Rating (Moody's)	Aa1