Derivative Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Derivative [Line Items]
Notional amount of interest rate swaps	$ 13.9
Notional amount of nonhedging interest rate swaps	460.8
Interest rate swaps, net liability position	18.8
Collateral posted for interest rate swaps in a net liability position	18.3
Real Estate And Building Materials [Member]
Derivative [Line Items]
Derivative loss from industry concentration	3.8
Education [Member]
Derivative [Line Items]
Derivative loss from industry concentration	3.9
Manufacturing [Member]
Derivative [Line Items]
Derivative loss from industry concentration	$ 2.7