Segment Reporting (Schedule of Operating Profit by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information
Operating profit	$ 59,820	$ 59,129
OEM Segment
Segment Reporting Information
Operating profit	53,940	54,397
Aftermarket Segment
Segment Reporting Information
Operating profit	$ 5,880	$ 4,732

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