Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (loss) - Reclassifications of Accumulated Other Comprehensive Loss (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Amortization of defined benefit pension and postretirement plan items:
Income tax benefit	$ (23,945,000)		$ (22,085,000)		$ (19,296,000)
Other Comprehensive Income Loss Adjustments AOCI Swap Agreements	(735,000)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amortization of defined benefit pension and postretirement plan items:
Net of tax	(581,000)		(278,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Amortization of defined benefit pension and postretirement plan items:
Prior service cost	58,000	[1]	60,000	[1]
Net gain	(279,000)	[1]	(523,000)	[1]
Total before income taxes	(221,000)		(463,000)
Income tax benefit	89,000		185,000
Net of tax	(132,000)		(278,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Amortization of defined benefit pension and postretirement plan items:
Total before income taxes	(752,000)		0
Income tax benefit	303,000		0
Net of tax	(449,000)		0
Other Comprehensive Income Loss Adjustments AOCI Swap Agreements	(735,000)	[2]	0	[2]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	$ (17,000)	[2]	$ 0	[2]

[1] These amounts are included in the computation of net periodic benefits. See Note 16, Employee Benefit Plans, for additional details.

[2] These amounts are included in the effects of gains and losses from derivative instruments. See Note 7, Derivative Instruments, for additional details.