Derivative Instruments and Hedging Activities (Details Textual) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Derivative Instruments and Hedging Activities (Textual) [Abstract]
Forecasted debt issuance variable rate period	3-month LIBOR
Percentage of interest rate swap effectiveness			100.00%
Interest rate swap recorded in other comprehensive income	$ 23,000,000
Increase Decrease in Interest expense due to amortization of gain on discontinuation of interest rate swap agreement	5,000,000	5,000,000
Ineffective portion of the cash flow hedges	2,000,000
Loss from the termination of the interest rate swap agreement	23,000,000		23,000,000
Issued notes	400,000,000
Additional expense related to the cash flow hedge terminated	$ 500,000