Investment Securities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Schedule of Investments [Line Items]
Residential mortgage-backed securities and collateralized mortgage obligations, term	15 years
U.S. Treasury And Sponsored Entities Callable Notes [Member]
Schedule of Investments [Line Items]
Available-for-sale securities	599.1
U.S. Treasury And Sponsored Entities Callable Notes [Member] | Minimum [Member]
Schedule of Investments [Line Items]
Maturity period of U.S. treasury and sponsored entities callable notes	9 years
U.S. Treasury And Sponsored Entities Callable Notes [Member] | Maximum [Member]
Schedule of Investments [Line Items]
Maturity period of U.S. treasury and sponsored entities callable notes	15 years