Segment Reporting (Schedule of Operating Profit by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information
Operating profit	$ 47,755	$ 59,820
Operating Segments \| OEM Segment
Segment Reporting Information
Operating profit	40,408	53,940
Operating Segments \| Aftermarket Segment
Segment Reporting Information
Operating profit	$ 7,347	$ 5,880

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