Accumulated Other Comprehensive Earnings (Loss) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 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	703,433	$ 700,135
AOCI from 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	95	440
Reclassifications from accumulated other comprehensive loss	34	655
Other comprehensive earnings (loss) net of tax	129	1,095
Balance at the end of the period	53	(580)
AOCI from 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	(1,213)	1,552
Reclassifications from accumulated other comprehensive loss	(122)	(27)
Other comprehensive earnings (loss) net of tax	(1,335)	1,525
Balance at the end of the period	(221)	1,698
Investments
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(697)	(605)
Other comprehensive earnings (loss) before reclassifications	242	637
Reclassifications from accumulated other comprehensive loss		3
Other comprehensive earnings (loss) net of tax	242	640
Balance at the end of the period	(455)	35
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	4
Reclassifications from accumulated other comprehensive loss	(466)	(524)
Other comprehensive earnings (loss) net of tax	(462)	(524)
Balance at the end of the period	4,411	5,863
Foreign Currency Translation
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	3,091	(1,431)
Other comprehensive earnings (loss) net of tax	3,091	(1,431)
Balance at the end of the period	(22,369)	(23,075)
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	2,219	1,198
Reclassifications from accumulated other comprehensive loss	(554)	107
Other comprehensive earnings (loss) net of tax	1,665	1,305
Balance at the end of the period	$ (18,581)	$ (16,059)