Accumulated Other Comprehensive Loss (Changes in Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 1,920,158	$ 1,839,654	$ 2,909,286
Other comprehensive income (loss) before reclassifications	23,433	54,363	(116,986)
Income tax	8,060	(24,644)	18,384
Net other comprehensive income (loss) before reclassifications	31,493	29,719	(98,602)
Reclassifications	53,745	31,934	(2,636)
Net reclassifications	33,839	20,105	(1,660)
Total other comprehensive income (loss), net of tax	65,332	49,824	(100,262)
Balance, end of period	1,844,277	1,920,158	1,839,654
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(565,381)	(615,205)	(514,943)
Income tax benefit	(19,906)	(11,829)	976
Total other comprehensive income (loss), net of tax	65,332	49,824	(100,262)
Balance, end of period	(500,049)	(565,381)	(615,205)
Foreign currency translation adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(68,132)	(58,844)	(3,482)
Other comprehensive income (loss) before reclassifications	52,145	(7,591)	(48,309)
Income tax	(5,865)	(1,697)	(7,053)
Net other comprehensive income (loss) before reclassifications	46,280	(9,288)	(55,362)
Reclassifications	0	0	0
Income tax benefit	0	0	0
Net reclassifications	0	0	0
Total other comprehensive income (loss), net of tax	46,280	(9,288)	(55,362)
Balance, end of period	(21,852)	(68,132)	(58,844)
Marketable securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(1,194)	(1,094)	(700)
Other comprehensive income (loss) before reclassifications	1,896	(159)	(626)
Income tax	(702)	59	232
Net other comprehensive income (loss) before reclassifications	1,194	(100)	(394)
Reclassifications	0	0	0
Income tax benefit	0	0	0
Net reclassifications	0	0	0
Total other comprehensive income (loss), net of tax	1,194	(100)	(394)
Balance, end of period	0	(1,194)	(1,094)
Derivative financial instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	12,524	5,886	19,042
Other comprehensive income (loss) before reclassifications	(54,929)	28,176	38,008
Income tax	20,338	(10,436)	(14,079)
Net other comprehensive income (loss) before reclassifications	(34,591)	17,740	23,929
Reclassifications	7,644	(17,633)	(58,902)
Income tax benefit	(2,831)	6,531	21,817
Net reclassifications	4,813	(11,102)	(37,085)
Total other comprehensive income (loss), net of tax	(29,778)	6,638	(13,156)
Balance, end of period	(17,254)	12,524	5,886
Derivative financial instruments | Foreign currency contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	7,202	(18,253)	(59,730)
Derivative financial instruments | Commodity contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications		258	677
Derivative financial instruments | Treasury rate locks
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	442	362	151
Pension and postretirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(508,579)	(561,153)	(529,803)
Other comprehensive income (loss) before reclassifications	24,321	33,937	(106,059)
Income tax	(5,711)	(12,570)	39,284
Net other comprehensive income (loss) before reclassifications	18,610	21,367	(66,775)
Reclassifications	46,101	49,567	56,266
Income tax benefit	(17,075)	(18,360)	(20,841)
Net reclassifications	29,026	31,207	35,425
Total other comprehensive income (loss), net of tax	47,636	52,574	(31,350)
Balance, end of period	(460,943)	(508,579)	(561,153)
Pension and postretirement benefit plans; Prior service credits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	(1,153)	(1,784)	(2,782)
Pension and postretirement benefit plans; Actuarial losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications	$ 47,254	49,888	58,680
Pension and postretirement benefit plans; Curtailment and settlement losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassifications		$ 1,463	$ 368