Consolidated Statement of Other Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 83,096	$ 63,859	$ 114,932
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	98	(293)	(1,471)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	468	339	83
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	526	829	971
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	(156)	(197)	583
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	974	(17)	1,151
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	0	0	(96)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(77)	(81)	(85)
Defined Benefit Plan, Amortization of Gains (Losses)	440	593	727
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	(330)	(124)	(424)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,007	371	1,273
Other Comprehensive Income (Loss), Net of Tax	1,475	710	1,356
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	84,571	64,569	116,288
Net Income (Loss) Attributable to Noncontrolling Interest	(29)	(36)	85
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 84,600	$ 64,605	$ 116,203