Pension and Other Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 2017

Pension and Other Postretirement Benefit Expense [Abstract]

Schedule of Net Benefit Costs [Table Text Block]

	Three Months Ended March 31,
	Pension Benefits						Other Postretirement Benefits
In thousands	2017			2016			2017			2016
Service cost	$	1,870		$	1,944		$	98		$	121
Interest cost	4,472			4,574			274			300
Expected return on plan assets	(5,113		)	(5,017		)	—			—
Amortization of prior service costs	32			58			(117		)	(117		)
Amortization of net actuarial loss	3,621			3,502			138			192
Net periodic benefit cost	4,882			5,061			393			496
Amount allocated to construction	(1,521		)	(1,548		)	(132		)	(164		)
Amount deferred to regulatory balancing account(1)	(1,527		)	(1,627		)	—			—
Net amount charged to expense	$	1,834		$	1,886		$	261		$	332

Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]

	Three Months Ended March 31,
In thousands	2017			2016
Beginning balance	$	(6,951	)	$	(7,162	)
Amounts reclassified from AOCL:
Amortization of actuarial losses	225			321
Total reclassifications before tax	225			321
Tax (benefit) expense	(89		)	(127		)
Total reclassifications for the period	136			194
Ending balance	$	(6,815	)	$	(6,968	)