Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	$ (200,828)	$ (143,252)
Other comprehensive income before reclassifications to consolidated statements of income	86,515	(65,243)
Amounts reclassified from accumulated other comprehensive (loss) income to the consolidated statements of income	7,914	7,667
Total other comprehensive income (loss), net of tax	94,429	(57,576)	$ (43,799)
Accumulated other comprehensive income (loss)	(106,399)	(200,828)	(143,252)
Gains and Losses on Cash Flow Hedges
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	(227)	115
Other comprehensive income before reclassifications to consolidated statements of income	(231)	(739)
Amounts reclassified from accumulated other comprehensive (loss) income to the consolidated statements of income	530	397
Total other comprehensive income (loss), net of tax	299	(342)
Accumulated other comprehensive income (loss)	72	(227)	115
Pension and Other Postretirement Benefit Items
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	(114,570)	(105,703)
Other comprehensive income before reclassifications to consolidated statements of income	3,342	(16,137)
Amounts reclassified from accumulated other comprehensive (loss) income to the consolidated statements of income	7,384	7,270
Total other comprehensive income (loss), net of tax	10,726	(8,867)
Accumulated other comprehensive income (loss)	(103,844)	(114,570)	(105,703)
Foreign Currency Items
Changes in Accumulated Other Comprehensive Income by Component [Roll Forward]
Accumulated other comprehensive income (loss)	(86,031)	(37,664)
Other comprehensive income before reclassifications to consolidated statements of income	83,404	(48,367)
Amounts reclassified from accumulated other comprehensive (loss) income to the consolidated statements of income	0	0
Total other comprehensive income (loss), net of tax	83,404	(48,367)
Accumulated other comprehensive income (loss)	$ (2,627)	$ (86,031)	$ (37,664)