Commitments, Contingencies And Uncertainties (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		3 Months Ended			9 Months Ended			1 Months Ended
	Sep. 30, 2011 MT years securities	Sep. 01, 2009	Sep. 30, 2011 Purchase Power Agreement from New Plants, Original Agreement [Member] Southern New Mexico Plants [Member] mW electricalPlants	Sep. 30, 2011 Southern New Mexico Plant 2 [Member] Purchase Power Agreement from New Plants, Revised Agreement [Member] mW electricalPlants	Sep. 30, 2011 Purchase Power Agreement from New Plants, Revised Agreement [Member] Southern New Mexico Plant 1 [Member] mW electricalPlants	Sep. 30, 2011 Maximum [Member]	Sep. 30, 2011 Minimum [Member]	Sep. 30, 2011 Gila River Boundary Site [Member]	Apr. 30, 2011 Freeport-McMoran Copper and Gold Energy Services LLC [Member] mW
Increased power purchase quantity									125
Number of states affected by the Clean Air Transport Rule	27
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
Defined increase in GHG emissions, in tons						100,000	75,000
Accrual for environmental loss contingencies	$ 0.4
Accrued EPA Clean Site Costs	$ 0.1
Site Contingency Ownership Percentage Of Site								16.29%
Number of Solar Photovoltaic Plant(s)			2	1	1
Electric capacity, MW			12	10	12