Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2016

Summary of Derivative Instruments [Abstract]

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

	At December 31,
In thousands	2016		2015
Natural gas (in therms):
Financial	477,430		346,875
Physical	535,450		404,645
Foreign exchange	$	7,497	$	9,025

Income Statement Presentation of Derivative Instruments [Text Block]

	December 31, 2016						December 31, 2015
In thousands	Natural gas commodity			Foreign exchange			Natural gas commodity			Foreign exchange
Benefit (expense) to cost of gas	$	22,746		$	(130	)	$	(16,469	)	$	(419	)
Operating revenues	995			—			178			—
Amounts deferred to regulatory accounts on balance sheet	(23,394		)	130			16,351			419
Total gain in pre-tax earnings	$	347		$	—		$	60		$	—

Table Of Estimated Collateral Calls 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	$	—	$	—	$	—	$	—	$	16,086
Without Adequate Assurance Calls	—		—		—		—		13,784