Consolidated Statement of Other Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 63,859	$ 114,932	$ 258,626
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	(293)	(1,471)	(1,327)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	339	83	(1,082)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	829	971	245
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	(197)	583	0
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	(17)	1,151	(4,399)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit), Tax	0	0	1,024
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0	(96)	(87)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(81)	(85)	7
Defined Benefit Plan, Amortization of Gains (Losses)	593	727	540
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(124)	(424)	729
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	371	1,273	(2,186)
Other Comprehensive Income (Loss), Net of Tax	710	1,356	(3,268)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	64,569	116,288	255,358
Net Income (Loss) Attributable to Noncontrolling Interest	(36)	85	1,141
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 64,605	$ 116,203	$ 254,217