Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (236,516)	$ (331,120)	$ (265,406)	$ (354,998)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	5,915	152
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	22,505	19,803
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	470	3,923
Other Comprehensive Income (Loss), Net of Tax	28,890	23,878
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2,371)	(90,973)	(31,340)	(115,322)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	28,969	24,349
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Net of Tax	28,969	24,349
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	1,619	(1,869)	(1,081)	(2,232)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	5,915	152
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(3,215)	211
Other Comprehensive Income (Loss), Net of Tax	2,700	363
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(235,764)	(238,278)	$ (232,985)	$ (237,444)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(6,464)	(4,546)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	3,685	3,712
Other Comprehensive Income (Loss), Net of Tax	$ (2,779)	$ (834)