Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2016

Segment Reporting [Abstract]

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

In thousands	Utility		Gas Storage			Other			Total
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	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 from operations	119,215		5,032			1			124,248
Net income	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
2014
Operating revenues	$	731,578	$	22,235		$	224		$	754,037
Depreciation and amortization	72,660		6,533			—			79,193
Income from operations	138,711		3,987			267			142,965
Net income (loss)	58,587		(364		)	469			58,692
Capital expenditures	117,322		2,770			—			120,092
Total assets at December 31, 2014	2,766,493		273,712			16,121			3,056,326

Utility Margin [Table Text Block]

In thousands	2016		2015		2014
Utility margin calculation:
Utility operating revenues (1)	$	650,477	$	702,210	$	731,578
Less: Utility cost of gas	260,588		327,305		365,490
Environmental remediation expense	13,298		3,513		—
Utility margin	$	376,591	$	371,392	$	366,088