Long-Term Debt (Cash Flow Hedges) (Narrative 2) (Details) (USD $)	3 Months Ended							3 Months Ended		3 Months Ended			3 Months Ended
	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2011	Sep. 30, 2011 Other Current Liabilities [Member]	Dec. 31, 2010 Other Current Liabilities [Member]	Sep. 30, 2011 Other Noncurrent Liabilities [Member]	Dec. 31, 2010 Other Noncurrent Liabilities [Member]	Mar. 31, 2011 Interest Rate Cap [Member]	Dec. 31, 2007 Interest Rate Swaps [Member]	Mar. 31, 2011 Forward Starting Interest Rate Cap [Member]	Mar. 31, 2011 Forward Starting Interest Rate Cap From December 15, 2011 To December 15, 2012 [Member]	Mar. 31, 2011 Forward Starting Interest Rate Cap From December 15, 2012 To December 15, 2014 [Member]	Mar. 31, 2011 Forward Starting Interest Rate Swaps [Member]	Mar. 31, 2011 1.91% Forward Starting Interest Rate Swaps [Member]	Mar. 31, 2011 2.50% Forward Starting Interest Rate Swaps [Member]	Mar. 31, 2011 1.96% Forward Starting Interest Rate Swaps [Member]	Mar. 31, 2011 1.32% Forward Starting Interest Rate Swaps [Member]	Dec. 31, 2010 2.38% Forward Starting Interest Rate Swaps [Member]	Dec. 31, 2007 4.7625% Forward Starting Interest Rate Swaps [Member]	Dec. 31, 2007 4.865% Forward Starting Interest Rate Swaps [Member]	Oct. 18, 2010 4.865% Forward Starting Interest Rate Swaps [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Total notional amount of interest rate cash flow hedges		$ 1,000,000,000						$ 275,000,000	$ 150,000,000		$ 450,000,000	$ 400,000,000	$ 425,000,000	$ 225,000,000	$ 100,000,000	$ 25,000,000	$ 75,000,000	$ 600,000,000	$ 75,000,000	$ 75,000,000	$ 50,000,000
Interest rate percentage above which counterparty agrees to pay the difference		2.25%
Premium paid on interest rate cap	30,000	240,000								740,000
Maturity date of interest rate cash flow hedges								Dec. 15, 2011						May 15, 2015	Dec. 15, 2014	Dec. 15, 2013	Dec. 15, 2012	May 15, 2015	Oct. 05, 2012	Oct. 17, 2011
Number of additional forward starting interest rate swaps													6
Fixed rate payable on interest rate swap														1.91%	2.50%	1.96%	1.32%	2.38%	4.7625%	4.865%
Fair value of our interest rate swaps, liability		$ 10,000,000	$ 50,000,000	$ 1,000,000	$ 2,000,000	$ 49,000,000	$ 8,000,000