Derivatives (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2011
Derivative [Line Items]
Number of interest rate swaps with an aggregate notional amount	1
Aggregate notional amount of interest rate swap	$ 488,400,000
Derivative, net hedge ineffectiveness gain (loss)	0
Decrease in interest expense	100,000
Notional amount of interest rate derivatives	488,400,000
Termination value of derivatives in a net liability position	11,500,000
Collateral for derivative instruments with credit-risk-related contingent features
Collateral obligations for derivative counterparties	11,600,000
Interest Rate Swap [Member]
Derivative [Line Items]
Aggregate notional amount of interest rate swap	140,000,000
Notional amount of interest rate derivatives	$ 140,000,000