Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Nov. 01, 2015
Derivative [Line Items]
Financial Derivative, Nonmonetary Notional Amount	517,980,000	350,250,000	517,980,000	350,250,000	346,875,000
Derivative, Nonmonetary Notional Amount	398,980,000	296,250,000	398,980,000	296,250,000	404,645,000
Notional Amount of Foreign Currency Derivatives	$ 7,254	$ 7,920	$ 7,254	$ 7,920	$ 9,025
Target Hedge for 2015-16 gas year						75.00%
Operating revenues	99,183	138,280	354,712	399,945
Derivative, Loss on Derivative	7,592	7,900	23,087	22,000
Unrealized Gain On Derivatives			4,856
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	8,127	1,100	8,127	1,100	2,700
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(1,086)	(14,800)	(1,086)	(14,800)	(25,500)
Derivative Fair Value Of Derivative Net	7,041	13,700	7,041	13,700	$ 22,800
Natural Gas Commodity [Member]
Derivative [Line Items]
Cost of sales	23,237	10,020	6,858	(13,461)
Operating revenues	29	(616)	29	22
Less:Amounts deferred to regulatory accounts on balance sheet	(23,271)	(9,618)	(6,892)	13,447
Total Impact On Earnings	(5)	(214)	(5)	8
Foreign Currency [Member]
Derivative [Line Items]
Cost of sales	(87)	478	154	(263)
Operating revenues	0	0	0	0
Less:Amounts deferred to regulatory accounts on balance sheet	87	(478)	(154)	263
Total Impact On Earnings	$ 0	$ 0	$ 0	$ 0