Accumulated Other Comprehensive Earnings (Loss) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	$ 711,364
Balance at the end of the period	714,481	$ 705,330
Foreign Currency Derivatives | Foreign currency forward contracts
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(76)	(1,675)
Other comprehensive earnings (loss) before reclassifications	170	391
Reclassifications from accumulated other comprehensive loss		946
Other comprehensive earnings (loss) net of tax	170	1,337
Balance at the end of the period	94	(338)
Foreign Currency Derivatives | Commodity futures contracts
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	1,114	173
Other comprehensive earnings (loss) before reclassifications	(1,276)	2,424
Reclassifications from accumulated other comprehensive loss	(69)	(533)
Other comprehensive earnings (loss) net of tax	(1,345)	1,891
Balance at the end of the period	(231)	2,064
Investments
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(697)	(605)
Other comprehensive earnings (loss) before reclassifications	319	451
Reclassifications from accumulated other comprehensive loss		3
Other comprehensive earnings (loss) net of tax	319	454
Balance at the end of the period	(378)	(151)
Postretirement and Pension Benefits
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	4,873	6,387
Other comprehensive earnings (loss) before reclassifications	6
Reclassifications from accumulated other comprehensive loss	(700)	(786)
Other comprehensive earnings (loss) net of tax	(694)	(786)
Balance at the end of the period	4,179	5,601
Foreign Currency Translation Adjustment
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(25,460)	(21,644)
Other comprehensive earnings (loss) before reclassifications	2,875	(2,337)
Other comprehensive earnings (loss) net of tax	2,875	(2,337)
Balance at the end of the period	(22,585)	(23,981)
Accumulated Other Comprehensive Earnings ( Loss )
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(20,246)	(17,364)
Other comprehensive earnings (loss) before reclassifications	2,094	929
Reclassifications from accumulated other comprehensive loss	(769)	(370)
Other comprehensive earnings (loss) net of tax	1,325	559
Balance at the end of the period	$ (18,921)	$ (16,805)