CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
NET SALES	$ 176,888	$ 153,089	$ 336,048	$ 302,022
COSTS OF OPERATIONS	155,609	135,486	296,342	269,024
GROSS PROFIT	21,279	17,603	39,706	32,998
OPERATING EXPENSES:
Selling, general and administrative expenses	9,678	9,066	19,267	18,110
NON-OPERATING (INCOME) EXPENSES:
Interest expense, net	484	315	904	693
Other (income) expense, net	627	(470)	(288)	(484)
Total expense, net	10,789	8,911	19,883	18,319
INCOME BEFORE INCOME TAXES	10,490	8,692	19,823	14,679
INCOME TAX PROVISION	2,890	3,267	5,553	5,415
NET INCOME	$ 7,600	$ 5,425	$ 14,270	$ 9,264
BASIC INCOME PER COMMON SHARE (in dollars per share)	$ 0.67	$ 0.48	$ 1.25	$ 0.82
DILUTED INCOME PER COMMON SHARE (in dollars per share)	0.67	0.48	1.25	0.81
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.18	$ 0.18	$ 0.36	$ 0.36
WEIGHTED AVERAGE SHARES OUTSTANDING:
Basic (in shares)	11,384	11,365	11,384	11,357
Diluted (in shares)	11,393	11,383	11,393	11,381