Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2015

Segment Reporting [Abstract]

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

In thousands	Utility		Gas Storage			Other		Total
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	2,800,018		261,750			14,924		3,076,692
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	2,775,011		273,813			16,121		3,064,945
2013
Operating revenues	$	727,182	$	31,112		$	224	$	758,518
Depreciation and amortization	69,420		6,485			—		75,905
Income from operations	128,066		14,669			11		142,746
Net income	54,920		5,569			49		60,538
Capital expenditures	137,466		1,458			—		138,924
Total assets at December 31, 2013	2,644,367		310,097			16,447		2,970,911

Utility Margin [Table Text Block]

In thousands	2015		2014		2013
Utility margin calculation:
Utility operating revenues (1)	$	702,210	$	731,578	$	727,182
Less: Utility cost of gas	327,305		365,490		373,298
Environmental remediation expense	3,513		—		—
Utility margin	$	371,392	$	366,088	$	353,884

⁽¹⁾   Utility operating revenues include environmental recovery revenues, which are collections received from customers through our environmental recovery mechanism in Oregon, offset by environmental remediation expense.