CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
NET SALES	$ 711,706	$ 615,101	$ 601,119
COSTS OF OPERATIONS	628,370	548,000	536,840
GROSS PROFIT	83,336	67,101	64,279
OPERATING EXPENSES:
Selling, general and administrative expenses	39,542	35,561	32,318
NON-OPERATING (INCOME) EXPENSES
Interest expense, net	1,878	1,588	1,161
Other (income) expense, net	253	(387)	(277)
Total expense, net	41,673	36,762	33,202
INCOME BEFORE INCOME TAXES	41,663	30,339	31,077
INCOME TAX PROVISION	7,917	7,323	11,155
NET INCOME	$ 33,746	$ 23,016	$ 19,922
BASIC INCOME PER COMMON SHARE (in dollars per share)	$ 2.96	$ 2.02	$ 1.76
DILUTED INCOME PER COMMON SHARE (in dollars per share)	2.96	2.02	1.75
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.72	$ 0.72	$ 0.68
WEIGHTED AVERAGE SHARES OUTSTANDING:
Basic (in shares)	11,388	11,368	11,346
Diluted (in shares)	11,393	11,385	11,374