Segment Reporting (Schedule of Operating Profit by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information
Operating profit	$ 64,088	$ 63,040	$ 123,908	$ 122,169
Operating Segments | OEM Segment
Segment Reporting Information
Operating profit	53,591	56,445	107,531	110,842
Operating Segments | Aftermarket Segment
Segment Reporting Information
Operating profit	$ 10,497	$ 6,595	$ 16,377	$ 11,327