Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Period opening balance		$ (55,548)	$ (70,863)
Net current period other comprehensive income ending balance	[1]	655	1,557
Period closing balance		(54,893)	(69,306)
Amortization of actuarial loss included in net periodic cost, before tax		(1,500)	(3,100)
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax		400	500
Other comprehensive income (loss), tax		400	1,000
Defined Benefit Pension Plan Adjustments
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Period opening balance		(55,548)	(70,863)
Net current period other comprehensive income ending balance	[1]	655	1,557
Period closing balance		$ (54,893)	$ (69,306)

[1] For the three months ended March 31, 2016 and 2015, net periodic costs associated with our pension and other postretirement employee benefit, or OPEB, plans included in other comprehensive income and reclassified from accumulated other comprehensive loss included $1.5 million and $3.1 million, respectively, of actuarial loss amortization, as well as $0.4 million and $0.5 million, respectively, of prior service credit amortization, all net of tax totaling $0.4 million and $1.0 million, respectively. These accumulated other comprehensive loss components are included in the computation of net periodic pension and OPEB costs in Note 10, “Pension and Other Postretirement Employee Benefit Plans.”