Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2016

Accounting Policies [Abstract]

Schedule of Regulatory Assets [Table Text Block]

	Regulatory Assets
	June 30,				December 31,
In thousands	2016		2015		2015
Current:
Unrealized loss on derivatives(1)	$	3,439	$	15,017	$	22,092
Gas costs	9,571		19,070		8,717
Environmental costs(2)	9,610		—		9,270
Decoupling(3)	14,170		17,736		18,775
Other(4)	12,214		11,193		10,324
Total current	$	49,004	$	63,016	$	69,178
Non-current:
Unrealized loss on derivatives(1)	$	474	$	1,077	$	3,447
Pension balancing(5)	48,761		38,255		43,748
Income taxes	40,106		44,767		43,049
Pension and other postretirement benefit liabilities	177,596		193,356		184,223
Environmental costs(2)	65,983		49,917		76,584
Gas costs	1,487		2,472		1,949
Decoupling(3)	1,776		3,186		6,349
Other(4)	8,786		9,776		11,362
Total non-current	$	344,969	$	342,806	$	370,711

Schedule of Regulatory Liabilities [Table Text Block]

	Regulatory Liabilities
	June 30,				December 31,
In thousands	2016		2015		2015
Current:
Gas costs	$	12,501	$	20,087	$	14,157
Unrealized gain on derivatives(1)	7,428		1,015		2,659
Other(4)	7,371		5,610		13,111
Total current	$	27,300	$	26,712	$	29,927
Non-current:
Gas costs	$	1,622	$	3,615	$	8,869
Unrealized gain on derivatives(1)	3,541		1,369		27
Accrued asset removal costs(6)	332,627		320,206		327,047
Other(4)	3,469		3,456		3,344
Total non-current	$	341,259	$	328,646	$	339,287