Accumulated Other Comprehensive Earnings (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period			$ 759,854
Balance at the end of the period	$ 760,965	$ 758,329	760,965	$ 758,329
Foreign Currency Translation
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(26,432)	(23,563)	(23,368)	(24,159)
Other comprehensive earnings (loss) before reclassifications	328	(353)	(2,736)	243
Other comprehensive earnings (loss) net of tax	328	(353)	(2,736)	243
Balance at the end of the period	(26,104)	(23,916)	(26,104)	(23,916)
Investments
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	2,647	494	882	(1,516)
Other comprehensive earnings (loss) before reclassifications	(350)	278	1,415	2,288
Reclassifications from accumulated other comprehensive loss		26		26
Other comprehensive earnings (loss) net of tax	(350)	304	1,415	2,314
Balance at the end of the period	2,297	798	2,297	798
Foreign Currency Derivatives
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	324	(13)	10	(309)
Other comprehensive earnings (loss) before reclassifications	146	(105)	258	191
Reclassifications from accumulated other comprehensive loss	(62)	25	140	25
Other comprehensive earnings (loss) net of tax	84	(80)	398	216
Balance at the end of the period	408	(93)	408	(93)
Commodity Derivatives
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(70)	(84)	92	(444)
Other comprehensive earnings (loss) before reclassifications	316	(268)	36	(104)
Reclassifications from accumulated other comprehensive loss	69	270	187	466
Other comprehensive earnings (loss) net of tax	385	2	223	362
Balance at the end of the period	315	(82)	315	(82)
Postretirement and Pension Benefits
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	1,627	3,629	2,139	4,206
Reclassifications from accumulated other comprehensive loss	(255)	(288)	(767)	(865)
Other comprehensive earnings (loss) net of tax	(255)	(288)	(767)	(865)
Balance at the end of the period	1,372	3,341	1,372	3,341
Accumulated Other Comprehensive Earnings ( Loss )
Accumulated other comprehensive earnings (loss), net of tax
Balance at the beginning of the period	(21,904)	(19,537)	(20,245)	(22,222)
Other comprehensive earnings (loss) before reclassifications	440	(448)	(1,027)	2,618
Reclassifications from accumulated other comprehensive loss	(248)	33	(440)	(348)
Other comprehensive earnings (loss) net of tax	192	(415)	(1,467)	2,270
Balance at the end of the period	$ (21,712)	$ (19,952)	$ (21,712)	$ (19,952)