CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Net sales	$ 626,053	$ 612,690	$ 1,159,227	$ 1,104,009
Cost of sales	538,403	527,375	1,002,887	954,576
Gross profit	87,650	85,315	156,340	149,433
General and administrative expenses	26,509	25,778	56,649	50,887
Selling expenses	8,494	8,556	16,717	16,901
Amortization of intangible assets	5,109	4,940	10,238	9,881
Acquisition expenses	0	0	0	68
Income from operations	47,538	46,041	72,736	71,696
Other income (expense):
Interest expense	(7,020)	(7,151)	(14,110)	(14,605)
Other, net	1,081	4,037	912	11,953
Other expense, net	(5,939)	(3,114)	(13,198)	(2,652)
Income before income tax	41,599	42,927	59,538	69,044
Income tax expense	10,639	11,025	13,798	15,870
Net income	$ 30,960	$ 31,902	$ 45,740	$ 53,174
Net income per share:
Basic (in usd per share)	$ 0.56	$ 0.55	$ 0.83	$ 0.92
Diluted (in usd per share)	$ 0.56	$ 0.54	$ 0.82	$ 0.89
Weighted average common shares outstanding (in thousands):
Basic (in shares)	55,197	57,879	55,233	57,836
Diluted (in shares)	55,668	59,274	55,719	60,023
Dividends declared per share (in usd per share)	$ 0.080	$ 0.075	$ 0.160	$ 0.150