CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net sales	$ 2,267,278	$ 1,767,161	$ 1,845,444
Cost of sales	1,983,627	1,506,286	1,519,910
Gross profit	283,651	260,875	325,534
General and administrative expenses	95,114	77,825	74,129
Selling expenses	33,046	25,588	27,270
Amortization of intangible assets	19,468	17,041	19,940
Acquisition expenses	68	9,605	0
Impairment	24,968	0	1,663
Income from operations	110,987	130,816	202,532
Other income (expense):
Interest expense	(28,759)	(16,400)	(15,663)
Other, net	13,776	8,122	(1,452)
Other expense, net	(14,983)	(8,278)	(17,115)
Income before income tax	96,004	122,538	185,417
Income tax expense	26,583	11,116	65,984
Net income	$ 69,421	$ 111,422	$ 119,433
Net income per share:
Basic (in usd per share)	$ 1.22	$ 1.88	$ 1.87
Diluted (in usd per share)	$ 1.19	$ 1.78	$ 1.82
Weighted average common shares outstanding (in thousands):
Basic (in shares)	56,996	59,358	63,729
Diluted (in shares)	58,430	62,599	65,762
Dividends declared per share (in usd per share)	$ 0.305	$ 0.255	$ 0.06