Fair Value Measurements Valuation Technicques for Measurement with Unobservable Inputs (Details) (USD $)					6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended					3 Months Ended		6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Commodity Contract [Member]	Dec. 31, 2013 Commodity Contract [Member]	Jun. 30, 2014 Electric portfolio [Member] Discounted cash flow [Member] Low [Member]	Dec. 31, 2013 Electric portfolio [Member] Discounted cash flow [Member] Low [Member]	Jun. 30, 2014 Electric portfolio [Member] Discounted cash flow [Member] High [Member]	Dec. 31, 2013 Electric portfolio [Member] Discounted cash flow [Member] High [Member]	Jun. 30, 2014 Electric portfolio [Member] Discounted cash flow [Member] Weighted Average [Member]	Dec. 31, 2013 Electric portfolio [Member] Discounted cash flow [Member] Weighted Average [Member]	Jun. 30, 2014 Natural gas portfolio [Member] Discounted cash flow [Member] Low [Member]	Dec. 31, 2013 Natural gas portfolio [Member] Discounted cash flow [Member] Low [Member]	Jun. 30, 2014 Natural gas portfolio [Member] Discounted cash flow [Member] High [Member]	Dec. 31, 2013 Natural gas portfolio [Member] Discounted cash flow [Member] High [Member]	Jun. 30, 2014 Natural gas portfolio [Member] Discounted cash flow [Member] Weighted Average [Member]	Dec. 31, 2013 Natural gas portfolio [Member] Discounted cash flow [Member] Weighted Average [Member]	Jun. 30, 2014 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Subsidiaries [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Subsidiaries [Member]	Jun. 30, 2014 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Parent Company [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value, Measurements, Recurring [Member] Parent Company [Member]	Jun. 30, 2014 Electric portfolio [Member]	Jun. 30, 2013 Electric portfolio [Member]	Jun. 30, 2014 Electric portfolio [Member]	Jun. 30, 2013 Electric portfolio [Member]	Jun. 30, 2014 Electric portfolio [Member] Level 3 [Member] Fair Value, Measurements, Recurring [Member] Subsidiaries [Member] Commodity Contract [Member]		Dec. 31, 2013 Electric portfolio [Member] Level 3 [Member] Fair Value, Measurements, Recurring [Member] Subsidiaries [Member] Commodity Contract [Member]		Jun. 30, 2014 Natural gas portfolio [Member] Level 3 [Member] Fair Value, Measurements, Recurring [Member] Subsidiaries [Member] Commodity Contract [Member]		Dec. 31, 2013 Natural gas portfolio [Member] Level 3 [Member] Fair Value, Measurements, Recurring [Member] Subsidiaries [Member] Commodity Contract [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts																					$ 4,700,000	$ (15,600,000)	$ 100,000	$ (14,200,000)
Derivative Assets			52,083,000	26,600,000													13,845,000	6,491,000							11,020,000	[1]	3,818,000	[1]	2,825,000	[1]	2,673,000	[1]
Derivative Liability			33,102,000	72,988,000													18,811,000	22,273,000	0	0					15,713,000	[1]	19,239,000	[1]	3,098,000	[1]	3,034,000	[1]
Price (per MWh)					19.08	17.06	44.36	47.09	35.77	38.74
Price (per MMBtu)											3.84	3.62	4.09	4.19	4.02	3.78
Fair Value measurement, sensitivity analysis, hypothetical increase or decrease of market prices, result on fair value	10.00%
Fair Value Measurements, Sensitivity Analysis, Hypothetical Increase or Decrease of Market Prices, Result on Fair Value	$ 8,700,000	$ 7,000,000

[1] 1 The valuation techniques, unobservable inputs and ranges are the same for asset and liability positions