Commitments, Contingencies And Uncertainties (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	6 Months Ended
	Apr. 30, 2011 mW	Jun. 30, 2011 years MT	Sep. 01, 2009
Increased power purchase quantity	125
Estimated allowances under CAIR		$ 0.3
Carbon dioxide emissions from stationary sources, metric tons per year		25,000
Required reduction in GHG emissions per year from 2012 through 2020		2.00%
Carbon dioxide emissions from industrial and electric generating facilities, metric tons per year		25,000
Reduction in emissions of industrial and electric generating facilities per year		3.00%
Number of facilities required to inventory emissions			10,000
Accrual for environmental loss contingencies		0.4
Site's environmental loss contingency		0.4
Maximum [Member]
Defined increase in GHG emissions, in tons		100,000
Minimum [Member]
Defined increase in GHG emissions, in tons		75,000
Gila River Boundary Site [Member]
Percentage of ownership in site		16.29%
Environmental exit costs anticipated cost		$ 0.1
Clean Air Transport Rule [Member]
Number of states affected by the Clean Air Transport Rule		27