Unrealized and Realized Gain/Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financial [Member]
Derivative [Line Items]
Derivative, Loss on Derivative	$ 1,900		$ 15,600
Derivative, Gain on Derivative		$ 1,000		$ 1,000
Natural gas commodity
Derivative [Line Items]
Amounts deferred to regulatory accounts on balance sheet	(4,285)	2,548	(1,305)	19,895
Total gain (loss) in pre-tax earnings	(98)	10	(43)	(435)
Foreign exchange
Derivative [Line Items]
Amounts deferred to regulatory accounts on balance sheet	(210)	(51)	0	(275)
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	4,473	(2,566)	1,384	(19,081)
Benefit (expense) to cost of gas | Foreign exchange
Derivative [Line Items]
Gain (loss) on derivative, net	210	51	0	275
Operating Expense [Member] | Natural gas commodity
Derivative [Line Items]
Gain (loss) on derivative, net	(286)	28	(122)	(1,249)
Operating Expense [Member] | Foreign exchange
Derivative [Line Items]
Gain (loss) on derivative, net	$ 0	$ 0	$ 0	$ 0