Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2016

Accounting Policies [Abstract]

Schedule of Regulatory Assets [Table Text Block]

	Regulatory Assets
	March 31,				December 31,
In thousands	2016		2015		2015
Current:
Unrealized loss on derivatives(1)	$	17,313	$	23,242	$	22,092
Gas costs	7,978		19,653		8,717
Environmental costs(2)	9,096		—		9,270
Decoupling(3)	13,235		11,696		18,775
Other(4)	13,902		13,111		10,324
Total current	$	61,524	$	67,702	$	69,178
Non-current:
Unrealized loss on derivatives(1)	$	1,237	$	1,117	$	3,447
Pension balancing(5)	46,247		35,374		43,748
Income taxes	40,106		44,767		43,049
Pension and other postretirement benefit liabilities	180,909		197,601		184,223
Environmental costs(2)	67,999		50,175		76,584
Gas costs	2,462		4,334		1,949
Decoupling(3)	2,641		4,370		6,349
Other(4)	9,789		10,683		11,362
Total non-current	$	351,390	$	348,421	$	370,711

Schedule of Regulatory Liabilities [Table Text Block]

	Regulatory Liabilities
	March 31,				December 31,
In thousands	2016		2015		2015
Current:
Gas costs	$	22,098	$	12,774	$	14,157
Unrealized gain on derivatives(1)	1,960		436		2,659
Other(4)	11,538		11,053		13,111
Total current	$	35,596	$	24,263	$	29,927
Non-current:
Gas costs	$	9,221	$	4,729	$	8,869
Unrealized gain on derivatives(1)	452		117		27
Accrued asset removal costs(6)	331,000		315,946		327,047
Other(4)	6,088		5,632		3,344
Total non-current	$	346,761	$	326,424	$	339,287