Revenue Revenue by end customer (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Sales	$ 967,391	$ 902,051
Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	925,012
Commercial [Member]
Disaggregation of Revenue [Line Items]
Sales	15,084
Other Customers [Member]
Disaggregation of Revenue [Line Items]
Sales	27,295
North America [Member]
Disaggregation of Revenue [Line Items]
Sales	499,178
North America [Member] | Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	488,737
North America [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Sales	5,353
North America [Member] | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Sales	5,088
Europe [Member]
Disaggregation of Revenue [Line Items]
Sales	292,401
Europe [Member] | Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	260,656
Europe [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Sales	9,580
Europe [Member] | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Sales	22,165
Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Sales	149,175
Asia Pacific [Member] | Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	149,169
Asia Pacific [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Sales	6
Asia Pacific [Member] | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Sales	0
South America [Member]
Disaggregation of Revenue [Line Items]
Sales	26,637
South America [Member] | Automotive [Member]
Disaggregation of Revenue [Line Items]
Sales	26,450
South America [Member] | Commercial [Member]
Disaggregation of Revenue [Line Items]
Sales	145
South America [Member] | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Sales	$ 42