Derivative Instruments (Impact of Derivative Instruments Designated as Cash Flow Hedges) (Details) (Cash Flow Hedging, Treasury Lock, Interest Expense, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Cash Flow Hedging | Treasury Lock | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income	$ (813)	$ 0	$ (813)	$ 0