Segment Reporting (Schedule of Operating Profit by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information
Operating profit	$ 45,353	$ 47,927	$ 169,261	$ 170,096
Operating Segments | OEM Segment
Segment Reporting Information
Operating profit	36,905	41,025	144,436	151,867
Operating Segments | Aftermarket Segment
Segment Reporting Information
Operating profit	$ 8,448	$ 6,902	$ 24,825	$ 18,229