Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Net sales	$ 269,059	$ 372,587	$ 835,266	$ 1,120,947
Cost of sales	176,908	234,421	532,214	717,370
Selling and administrative expenses	60,908	70,581	212,380	228,385
Total operating costs and expenses	237,816	305,002	744,594	945,755
Operating income	31,243	67,585	90,672	175,192
Interest expense	3,701	5,344	11,924	15,856
Other expense (income), net	47	2,524	2,700	6,043
Income before income taxes	27,495	59,717	76,048	153,293
Income taxes	12,137	13,948	30,390	35,916
Net income	$ 15,358	$ 45,769	$ 45,658	$ 117,377
Per common share:
Basic (in dollars per share)	$ 0.30	$ 0.90	$ 0.90	$ 2.29
Diluted (in dollars per share)	$ 0.30	$ 0.89	$ 0.89	$ 2.27
Weighted average common shares outstanding:
Basic (in shares)	50,833,157	50,926,521	50,886,094	51,276,801
Diluted (in shares)	50,937,093	51,230,845	51,123,024	51,718,574