Contingencies (Details) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2008	Dec. 31, 2005	Sep. 30, 2010	Sep. 30, 2008	Dec. 31, 2003
Loss Contingencies [Line Items]
Customer refund for Trojan Investment, net of Interest					$ 15,400,000
Interest Rate Applied to Trojan Refund					9.60%
Refund to customers for Trojan Investment including interest					33,100,000
Class action damages sought						260,000,000
Annual charges for state and federal income taxes			92,600,000
Deferred Liability Under Sb 408 For 2005			26,500,000
Daily Penalty Sought Per Violation Before March 15 2004					27,500
Daily Penalty Sought Per Violation After March 15 2004					32,500
Payable for environmental projects	2,500,000
Payable for legal expenses	1,000,000
Settlement Expenses For Sierra Club Claim	2,000,000
Total penalties and damages asserted in Sierra Club Lawsuit					60,000,000
Maximum civil penalties the EPA is authorized to impose under the CAA for violations of the NSPS				25,000
Maximum civil penalties the EPA is authorized to impose under the CAA for violations of the NSPS - upper range				37,500
Repayments of Pollution Control Bond		$ 5,800,000