Unrealized and Realized Gain/Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Document Period End Date			Jun. 30, 2018
Financial [Member]
Derivative [Line Items]
Derivative, Loss on Derivative	$ 4,700		$ 13,700
Derivative, Gain on Derivative		$ 300		$ 300
Natural gas commodity
Derivative [Line Items]
Amounts deferred to regulatory accounts on balance sheet	(2,915)	5,263	2,980	17,347
Total gain (loss) in pre-tax earnings	134	(18)	55	(445)
Foreign exchange
Derivative [Line Items]
Amounts deferred to regulatory accounts on balance sheet	56	(216)	210	(224)
Total gain (loss) in pre-tax earnings	0	0	0	0
Benefit (expense) to cost of gas | Natural gas commodity
Derivative [Line Items]
Gain (loss) on derivative, net	2,658	(5,172)	(3,089)	(16,515)
Benefit (expense) to cost of gas | Foreign exchange
Derivative [Line Items]
Gain (loss) on derivative, net	(56)	216	(210)	224
Operating Expense [Member] | Natural gas commodity
Derivative [Line Items]
Gain (loss) on derivative, net	391	(109)	164	(1,277)
Operating Expense [Member] | Foreign exchange
Derivative [Line Items]
Gain (loss) on derivative, net	$ 0	$ 0	$ 0	$ 0