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Summary of Significant Accounting Policies Concentration Risk (Details)	12 Months Ended
	Dec. 31, 2018 Employee Customer	Dec. 31, 2017	Dec. 31, 2016
Sales Revenue, Total [Member] | Customer Concentration Risk [Member]
Concentration risk:
Number of major customers, Sales | Customer	4
Concentration Risk, Percentage	65.00%	65.00%	68.00%
Sales Revenue, Total [Member] | Geographic concentration risk | Mexico and Canada [Member]
Concentration risk:
Concentration Risk, Percentage	32.00%	36.00%	32.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member]
Concentration risk:
Concentration Risk, Accounts Receivable, Number of major customers | Customer	4
Concentration Risk, Percentage	64.00%	74.00%
Number of employees, geographic area | Labor force concentration risk
Concentration risk:
Concentration risk, number of employees	2,190
Number of employees, geographic area | Labor force concentration risk | MEXICO
Concentration risk:
Concentration risk, number of employees	1,033
Number of employees, geographic area | Labor force concentration risk | United States
Concentration risk:
Concentration risk, number of employees	886
Number of employees, geographic area | Labor force concentration risk | CANADA
Concentration risk:
Concentration risk, number of employees	271
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | International Association of Machinists and Aerospace Workers
Concentration risk:
Concentration risk, number of employees	372
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | Sindicato de Jorneleros y Obreros
Concentration risk:
Concentration risk, number of employees	876
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | United Food & Commercial Workers Canada [Member] [Member]
Concentration risk:
Concentration risk, number of employees	221
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | Sindicato de trabajadores de la industria metalica y del comercio del estado de Nuevo Leon Presidente Benito Juarez Garcia C.T.M. [Member]
Concentration risk:
Concentration risk, number of employees	26

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

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-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
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-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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