Energy Purchase Contracts (Future Contractual Commitments For Power Resources And Natural Gas Resources) (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Energy Purchase Contracts [Line Items]
2016	$ 340,895
2017	233,231
2018	214,519
2019	202,179
2020	150,134
Thereafter	1,265,971
Total	2,406,929
Power Resources [Member]
Energy Purchase Contracts [Line Items]
2016	261,560
2017	168,831
2018	149,375
2019	145,074
2020	104,688
Thereafter	838,536
Total	1,668,064
Natural Gas Resources [Member]
Energy Purchase Contracts [Line Items]
2016	79,335
2017	64,400
2018	65,144
2019	57,105
2020	45,446
Thereafter	427,435
Total	738,865
Generation Transmission And Distribution Facilities [Member]
Energy Purchase Contracts [Line Items]
2016	33,694
2017	31,134
2018	26,405
2019	31,117
2020	31,811
Thereafter	192,295
Total	$ 346,456