Debt Obligations 2 Narrative (Details) (USD $)	0 Months Ended	12 Months Ended											12 Months Ended				12 Months Ended
	Nov. 01, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Term Loan 2013 [Member]	Feb. 18, 2011 Term Loan 2013 [Member]	Dec. 31, 2010 Term Loan 2013 [Member]	Dec. 31, 2011 Term Loan Due February 2015 [Member]	Dec. 31, 2010 Term Loan Due February 2015 [Member]	Dec. 31, 2011 Term Loan Due June 2012 [Member]	Feb. 18, 2011 Term Loan Due June 2012 [Member]	Dec. 31, 2010 Term Loan Due June 2012 [Member]	Dec. 31, 2011 Credit Facilities [Member]	Jul. 31, 2011 Credit Facilities [Member]	Feb. 18, 2011 Credit Facilities [Member]	Dec. 31, 2010 Credit Facilities [Member]	Dec. 31, 2011 Restrictive Covenants [Member]	Dec. 31, 2011 Revolver 2011 [Member]	Dec. 31, 2011 First Mortgage Bond [Member]
Debt Instrument [Line Items]
Variable debt rate	three-month LIBOR rate plus 3.0175 percent				LIBOR plus 2.125 percent
Debt at fixed interest rates		$ 2,830,000,000
Fixed interest rate minimum		3.63%
Fixed interest rate maximum		9.44%
Debt at variable interest rates		667,400,000
Variable interest rate minimum		0.85%
Variable interest rate maximum		3.45%
Repayment of long-term debt obligation		18,556,000	140,947,000	60,623,000
Effective interest rate					2.40%	2.38%	2.39%			0.85%	0.82%	0.81%	1.88%		1.86%	3.02%
Credit facilities/credit agreement		200,000,000	297,051,000							342,400,000	342,400,000	360,400,000		2,000,000		297,100,000
Time period for individual borrowings, minimum													15
Time period for individual borrowings, maximum													180
Debt to capitalization ratio maximum permitted																		65.00%	70.00%
Interest coverage ratio																	2.00
Debt instrument, face amount					250,000,000			455,000,000		465,000,000			550,000,000
Long-term Debt					$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 455,000,000	$ 455,000,000				$ 200,000,000		$ 148,300,000
Interest and Fee Rate Bases													LIBOR, plus 162.5 basis points, and 25 basis points, respectively