Industry Segment and Geographic Data, Reportable Segments (Details) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Segment		Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($)
Financial information for reportable segment [Abstract]
Number of reportable operating segments | Segment										2
Net sales		$ 282,738	$ 343,609	$ 247,939	$ 254,302	$ 241,252	$ 307,723	$ 305,172	$ 283,766	$ 1,128,588	[1]	$ 1,137,913	[1]	$ 1,092,051	[1]
Depreciation and amortization										26,323		25,809		24,104
Operating income (loss)										108,895		94,495		81,268
Investment in unconsolidated affiliates		40,507				38,858				40,507		38,858		32,469
Capital expenditures										17,820		16,185		20,141
Total assets		956,540				903,854				956,540		903,854		819,116
Intersegment Revenues [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									0		0		0
Engine Management [Member] | Reportable Segments [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									835,685		849,161		803,487
Depreciation and amortization										20,417		19,463		17,858
Operating income (loss)										111,217		103,808		84,844
Investment in unconsolidated affiliates		2,428				2,243				2,428		2,243		2,158
Capital expenditures										13,496		12,593		11,435
Total assets		618,210				594,953				618,210		594,953		532,092
Engine Management [Member] | Intersegment Revenues [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									15,952		19,569		23,367
Temperature Control [Member] | Reportable Segments [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									281,954		278,355		278,456
Depreciation and amortization										4,035		4,568		4,704
Operating income (loss)										21,296		13,667		14,586
Investment in unconsolidated affiliates		38,079				36,615				38,079		36,615		30,311
Capital expenditures										1,988		2,273		7,245
Total assets		230,111				216,591				230,111		216,591		202,411
Temperature Control [Member] | Intersegment Revenues [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									6,162		6,545		8,160
Other [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									10,949		10,397		10,108
Depreciation and amortization										1,871		1,778		1,542
Operating income (loss)										(23,618)		(22,980)		(18,162)
Investment in unconsolidated affiliates		0				0				0		0		0
Capital expenditures										2,336		1,319		1,461
Total assets		$ 108,219				$ 92,310				108,219		92,310		84,613
Other [Member] | Intersegment Revenues [Member]
Financial information for reportable segment [Abstract]
Net sales	[1]									$ (22,114)		$ (26,114)		$ (31,527)

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