Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	$ (106,399)	$ (200,828)
Other comprehensive income before reclassifications	27,873	18,422
Amounts reclassified from accumulated other comprehensive income	2,640	1,535
Net current-period other comprehensive income	30,513	19,957
Accumulated other comprehensive income (loss)	(95,217)	(180,871)
Accounting Standards Update 2018-02 [Member]
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Amounts reclassified from accumulated other comprehensive income	(19,331)
Gains and Losses on Cash Flow Hedges
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	72	(227)
Other comprehensive income before reclassifications	157	27
Amounts reclassified from accumulated other comprehensive income	239	56
Net current-period other comprehensive income	396	83
Accumulated other comprehensive income (loss)	468	(144)
Gains and Losses on Cash Flow Hedges | Accounting Standards Update 2018-02 [Member]
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Amounts reclassified from accumulated other comprehensive income	0
Pension and Other Postretirement Benefit Items
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	(103,844)	(114,570)
Other comprehensive income before reclassifications	763	(214)
Amounts reclassified from accumulated other comprehensive income	2,401	1,479
Net current-period other comprehensive income	3,164	1,265
Accumulated other comprehensive income (loss)	(120,011)	(113,305)
Pension and Other Postretirement Benefit Items | Accounting Standards Update 2018-02 [Member]
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Amounts reclassified from accumulated other comprehensive income	(19,331)
Foreign Currency Items
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	(2,627)	(86,031)
Other comprehensive income before reclassifications	26,953	18,609
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income	26,953	18,609
Accumulated other comprehensive income (loss)	24,326	$ (67,422)
Foreign Currency Items | Accounting Standards Update 2018-02 [Member]
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Amounts reclassified from accumulated other comprehensive income	$ 0