CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
NET SALES	$ 195,690	$ 153,363	$ 531,738	$ 455,385
COSTS OF OPERATIONS	174,214	137,713	470,556	406,737
GROSS PROFIT	21,476	15,650	61,182	48,648
OPERATING EXPENSES:
Selling, general and administrative expenses	9,450	8,580	28,717	26,690
NON-OPERATING (INCOME) EXPENSES:
Interest expense, net	525	469	1,429	1,162
Other (income) expense, net	76	(106)	(212)	(590)
Total expense, net	10,051	8,943	29,934	27,262
INCOME BEFORE INCOME TAXES	11,425	6,707	31,248	21,386
INCOME TAX PROVISION	2,748	2,251	8,301	7,666
NET INCOME	$ 8,677	$ 4,456	$ 22,947	$ 13,720
BASIC INCOME PER COMMON SHARE (in dollars per share)	$ 0.76	$ 0.39	$ 2.02	$ 1.21
DILUTED INCOME PER COMMON SHARE (in dollars per share)	0.76	0.39	2.01	1.21
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.18	$ 0.18	$ 0.54	$ 0.54
WEIGHTED AVERAGE SHARES OUTSTANDING:
Basic (in shares)	11,389	11,364	11,386	11,357
Diluted (in shares)	11,393	11,373	11,393	11,376