Fair Value Measurements Valuation Technicques for Measurement with Unobservable Inputs (Details) - Fair Value, Measurement Frequency [Domain] - Entity [Domain] $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) $ / MMBTU $ / MWh	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($) $ / MMBTU $ / MWh	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ 14,547	$ 4,966	$ 14,547	$ 4,966	$ 15,782	$ 17,692	$ 14,100	$ 15,709
Fair Value measurement, sensitivity analysis, hypothetical increase or decrease of market prices, result on fair value	10.00%		10.00%
Fair Value Measurements, Sensitivity Analysis, Hypothetical Increase or Decrease of Market Prices, Result on Fair Value	$ 3,800		$ 3,800				3,900
Commodity Contract [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets	21,088		21,088				24,348
Derivative Liability	167,748		$ 167,748				196,035
Electric portfolio [Member] | Discounted cash flow [Member] | Low [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh			15.17		21.79
Electric portfolio [Member] | Discounted cash flow [Member] | High [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh			38.00		35.46
Electric portfolio [Member] | Discounted cash flow [Member] | Weighted Average [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MWh) | $ / MWh			28.03		32.89
Natural gas portfolio [Member] | Discounted cash flow [Member] | Low [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MMBtu) | $ / MMBTU			1.71		3.11
Natural gas portfolio [Member] | Discounted cash flow [Member] | High [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MMBtu) | $ / MMBTU			3.54		3.83
Natural gas portfolio [Member] | Discounted cash flow [Member] | Weighted Average [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price (per MMBtu) | $ / MMBTU			2.79		3.28
Electric portfolio [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	15,370	4,693	$ 15,370	4,693	$ 15,421	16,091	12,061	14,606
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(3,800)	4,700	(8,800)	100
Natural gas portfolio [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ (823)	$ 273	$ (823)	$ 273	$ 361	$ 1,601	$ 2,039	$ 1,103