CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF OPERATIONS [Abstract]
Net sales	[1]	$ 1,116,143	$ 1,058,482	$ 971,975
Cost of sales		789,487	735,995	690,987
Gross profit		326,656	322,487	280,988
Selling, general and administrative expenses		223,584	221,658	206,287
Restructuring and integration expense (income)		6,173	3,957	(134)
Other income, net		1,275	1,195	1,025
Operating income		98,174	98,067	75,860
Other non-operating income (expense), net		597	2,059	(220)
Interest expense		2,329	1,556	1,537
Earnings from continuing operations before taxes		96,442	98,570	74,103
Provision for income taxes		52,812	36,158	25,983
Earnings from continuing operations		43,630	62,412	48,120
Loss from discontinued operations, net of income tax benefit of $3,769, $1,322 and $1,401		(5,654)	(1,982)	(2,102)
Net earnings		$ 37,976	$ 60,430	$ 46,018
Net earnings per common share - Basic:
Earnings from continuing operations (in dollars per share)		$ 1.92	$ 2.75	$ 2.11
Discontinued operations (in dollars per share)		(0.25)	(0.09)	(0.09)
Net earnings per common share - Basic (in dollars per share)		1.67	2.66	2.02
Net earnings per common share - Diluted:
Earnings from continuing operations (in dollars per share)		1.88	2.70	2.08
Discontinued operations (in dollars per share)		(0.24)	(0.08)	(0.09)
Net earnings per common share - Diluted (in dollars per share)		1.64	2.62	1.99
Dividend declared per share (in dollars per share)		$ 0.76	$ 0.68	$ 0.60
Average number of common shares (in shares)		22,726,491	22,722,517	22,811,862
Average number of common shares and dilutive common shares (in shares)		23,198,392	23,082,578	23,142,394

[1] Segment and product line net sales include intersegment sales in our Engine Management and Temperature Control segments.