Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2017

Accounting Policies [Abstract]

Schedule of Regulatory Assets [Table Text Block]

	Regulatory Assets
	March 31,				December 31,
In thousands	2017		2016		2016
Current:
Unrealized loss on derivatives(1)	$	1,580	$	17,313	$	1,315
Gas costs	2,757		7,978		6,830
Environmental costs(2)	7,574		9,096		9,989
Decoupling(3)	10,087		13,235		13,067
Other(4)	12,876		13,902		11,161
Total current	$	34,874	$	61,524	$	42,362
Non-current:
Unrealized loss on derivatives(1)	$	2,546	$	1,237	$	913
Pension balancing(5)	53,105		46,247		50,863
Income taxes	36,591		40,106		38,670
Pension and other postretirement benefit liabilities	179,586		180,909		183,035
Environmental costs(2)	62,227		67,999		63,970
Gas costs	114		2,462		89
Decoupling(3)	2,803		2,641		5,860
Other(4)	12,085		9,789		14,130
Total non-current	$	349,057	$	351,390	$	357,530

Schedule of Regulatory Liabilities [Table Text Block]

	Regulatory Liabilities
	March 31,				December 31,
In thousands	2017		2016		2016
Current:
Gas costs	$	13,741	$	22,098	$	8,054
Unrealized gain on derivatives(1)	2,870		1,960		16,624
Other(4)	16,600		11,538		15,612
Total current	$	33,211	$	35,596	$	40,290
Non-current:
Gas costs	$	4,740	$	9,221	$	1,021
Unrealized gain on derivatives(1)	46		452		3,265
Accrued asset removal costs(6)	345,614		331,000		341,107
Other(4)	7,187		6,088		3,926
Total non-current	$	357,587	$	346,761	$	349,319