Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Derivative Instruments [Abstract]

Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]

	At December 31,
In thousands	2017		2016
Natural gas (in therms):
Financial	429,100		477,430
Physical	520,268		535,450
Foreign exchange	$	7,669	$	7,497

Income Statement Presentation of Derivative Instruments [Text Block]

	December 31, 2017						December 31, 2016
In thousands	Natural gas commodity			Foreign exchange			Natural gas commodity			Foreign exchange
Benefit (expense) to cost of gas	$	(26,000	)	$	107		$	22,746		$	(130	)
Operating revenues	(1,021		)	—			995			—
Amounts deferred to regulatory accounts on balance sheet	26,665			(107		)	(23,394		)	130
Total gain (loss) in pre-tax earnings	$	(356	)	$	—		$	347		$	—

Table Of Estimated Collateral Calls Table [Table Text Block]

			Credit Rating Downgrade Scenarios
In thousands	(Current Ratings) A+/A3		BBB+/Baa1		BBB/Baa2		BBB-/Baa3			Specul-ative
With Adequate Assurance Calls	$	—	$	—	$	—	$	(5,428	)	$	(15,422	)
Without Adequate Assurance Calls	—		—		—		(5,428		)	(11,594		)