Risk Management and Hedging Activities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Physical purchase and sale of gas and electricity at fixed prices	$ 0	$ 0
Interest Rate Swap [Member]
Derivative [Line Items]
Pre-tax gain on cash flow hedges remaining in AOCI	14,900
Pre-tax gain on cash flow hedge to be reclassified within twelve months from AOCI to interest expense	300
Interest Rate Swap [Member] | Interest Expense [Member]
Derivative [Line Items]
Amount of gain reclassified from AOCI	$ 62