Segment Reporting (Tables)

3 Months Ended

Mar. 31, 2016

Segment Reporting [Abstract]

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

	Three Months Ended March 31,
In thousands	Utility		Gas Storage		Other		Total
2016
Operating revenues	$	250,104	$	5,369	$	56	$	255,529
Depreciation and amortization	18,760		1,634		—		20,394
Income from operations	72,295		1,726		51		74,072
Net income	35,852		736		53		36,641
Capital expenditures	29,177		877		—		30,054
Total assets at March 31, 2016	2,726,696		260,535		14,802		3,002,033
2015
Operating revenues	$	256,306	$	5,303	$	56	$	261,665
Depreciation and amortization	18,475		1,636		—		20,111
Income from operations	51,880		1,055		66		53,001
Net income	28,335		114		37		28,486
Capital expenditures	25,809		1,326		—		27,135
Total assets at March 31, 2015	2,688,304		270,905		14,903		2,974,112
Total assets at December 31, 2015	2,792,736		261,750		14,924		3,069,410

Utility Margin [Table Text Block]

	Three Months Ended March 31,
In thousands	2016		2015
Utility margin calculation:
Utility operating revenues(1)	$	250,104	$	256,306
Less: Utility cost of gas	108,411		125,705
Environmental remediation expense	5,029		—
Utility margin	$	136,664	$	130,601

⁽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.