Accounting Policies - Accumulated Other Comprehensive Loss by Component, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,828,532
Ending balance	2,988,229
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	5,063	$ (321,033)
Other comprehensive income (loss) before reclassifications	77,967	49,395
Amounts reclassified from accumulated other comprehensive income	0	0
Net current period other comprehensive income (loss)	77,967	49,395
Ending balance	83,030	(271,638)
Derivative contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	4,015	(2,957)
Other comprehensive income (loss) before reclassifications	920	903
Amounts reclassified from accumulated other comprehensive income	448	426
Net current period other comprehensive income (loss)	1,368	1,329
Ending balance	5,383	(1,628)
Pension and post retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(54,070)	(55,615)
Other comprehensive income (loss) before reclassifications	(847)	(3,363)
Amounts reclassified from accumulated other comprehensive income	520	592
Net current period other comprehensive income (loss)	(327)	(2,771)
Ending balance	(54,397)	(58,386)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(44,992)	(379,605)
Other comprehensive income (loss) before reclassifications	78,040	46,935
Amounts reclassified from accumulated other comprehensive income	968	1,018
Net current period other comprehensive income (loss)	79,008	47,953
Ending balance	$ 34,016	$ (331,652)