Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment [Table Text Block]

In thousands	Utility		Gas Storage			Other			Total
2017
Operating revenues	$	732,942	$	23,620		$	5,611		$	762,173
Depreciation and amortization	79,734		5,844			—			85,578
Income (loss) from operations (1)	132,807		(185,074		)	(960		)	(53,227		)
Net income (loss) (2)	60,509		(116,209		)	77			(55,623		)
Capital expenditures	211,672		1,923			—			213,595
Total assets at December 31, 2017	2,961,326		59,583			18,837			3,039,746
2016
Operating revenues	$	650,477	$	25,266		$	224		$	675,967
Depreciation and amortization	76,289		6,000			—			82,289
Income (loss) from operations	130,570		9,136			(426		)	139,280
Net income (loss) (3)	54,567		4,303			25			58,895
Capital expenditures	138,074		1,437			—			139,511
Total assets at December 31, 2016	2,806,627		256,333			16,841			3,079,801
2015
Operating revenues	$	702,210	$	21,356		$	225		$	723,791
Depreciation and amortization	74,410		6,513			—			80,923
Income (loss) from operations	119,215		5,032			1			124,248
Net income (loss) (3)	53,391		174			138			53,703
Capital expenditures	115,272		3,048			—			118,320
Total assets at December 31, 2015	2,791,623		261,750			16,037			3,069,410

Utility Margin [Table Text Block]

In thousands	2017		2016		2015
Utility margin calculation:
Utility operating revenues	$	732,942	$	650,477	$	702,210
Less: Utility cost of gas	325,019		260,588		327,305
Environmental remediation expense	15,291		13,298		3,513
Utility margin	$	392,632	$	376,591	$	371,392