Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012 derivative_instrument	Dec. 31, 2011 derivative_instrument
Interest rate swap contracts [Member] | Derivatives Designated as Cash Flow Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Number of derivative instruments held	3	3
Derivative asset notional amount	$ 33.0	$ 33.0
Pledged collateral to derivative counterparties	2.0	1.9
Interest rate swaps with customers [Member] | Derivatives not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative asset notional amount	70.5	61.6
Mirror swaps with counterparties [Member] | Derivatives not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative asset notional amount	$ 70.5	$ 61.6