Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Net sales	$ 253,631	$ 336,866	$ 556,425	$ 651,573
Cost of goods sold	217,132	290,956	474,153	564,337
Gross profit	36,499	45,910	82,272	87,236
Selling, general, and administrative expenses	20,755	23,846	43,044	48,844
Operating income	15,744	22,064	39,228	38,392
Net interest and other income	267	1,082	1,151	2,160
Income before income taxes	16,011	23,146	40,379	40,552
Provision for income taxes	3,664	5,364	9,424	9,359
Net income	$ 12,347	$ 17,782	$ 30,955	$ 31,193
Earnings per common and common equivalent share - basic (in usd per share)	$ 0.60	$ 0.85	$ 1.50	$ 1.49
Earnings per common and common equivalent share - diluted (in usd per share)	$ 0.60	$ 0.85	$ 1.50	$ 1.49
Weighted average common and common equivalent shares outstanding - basic (in shares)	20,496	20,898	20,646	20,891
Weighted average common and common equivalent shares outstanding - diluted (in shares)	20,537	20,988	20,696	20,985
Cash dividends declared per share (in usd per share)	$ 0.02	$ 0.02	$ 0.04	$ 0.04