CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF INCOME
NET SALES	$ 651,286	$ 818,166	$ 711,706
COSTS OF OPERATIONS	572,928	721,678	628,370
GROSS PROFIT	78,358	96,488	83,336
OPERATING EXPENSES:
Selling, general and administrative expenses	39,714	43,394	39,542
NON-OPERATING (INCOME) EXPENSES:
Interest expense, net	1,215	2,378	1,878
Other (income) expense, net	(668)	331	253
Total expense, net	40,261	46,103	41,673
INCOME BEFORE INCOME TAXES	38,097	50,385	41,663
INCOME TAX PROVISION	8,267	11,274	7,917
NET INCOME	$ 29,830	$ 39,111	$ 33,746
BASIC INCOME PER COMMON SHARE (in dollars per share)	$ 2.62	$ 3.43	$ 2.96
DILUTED INCOME PER COMMON SHARE (in dollars per share)	2.62	3.43	2.96
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.72	$ 0.72	$ 0.72
WEIGHTED AVERAGE SHARES OUTSTANDING:
Basic (in shares)	11,405	11,400	11,388
Diluted (in shares)	11,405	11,400	11,393