Valuation and Qualifying Accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 31,777	$ 27,631	$ 25,610
Additions Charged to Income or Regulatory Assets	512	1,569	2,021
Other Changes Deductions from Provisions	1,130	(2,577)
Ending Balance	31,159	31,777	27,631
Accumulated Provisions Not Deducted from Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	395,250	141,315	147,452
Additions Charged to Income or Regulatory Assets	46,792	333,371	52,050
Other Changes Deductions from Provisions	56,530	79,436	58,187
Ending Balance	$ 385,512	$ 395,250	$ 141,315