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Summary of Significant Accounting Policies - Concentration Risk (Details)	12 Months Ended
	Dec. 31, 2016 Customer Employee	Dec. 31, 2015	Dec. 31, 2014
Sales | Customer concentration risk
Concentration risk:
Number of major customers, Sales | Customer	4
Concentration risk percentage	78.00%	82.00%	87.00%
Sales | Geographic concentration risk | Mexico and Canada
Concentration risk:
Concentration risk percentage	32.00%	35.00%	30.00%
Accounts receivable | Customer concentration risk
Concentration risk:
Concentration Risk, Accounts Receivable, Number of major customers | Customer	4
Concentration risk percentage	75.00%	88.00%
Number of employees, geographic area | Labor force concentration risk
Concentration risk:
Concentration risk, number of employees	1,247
Number of employees, geographic area | Labor force concentration risk | United States
Concentration risk:
Concentration risk, number of employees	568
Number of employees, geographic area | Labor force concentration risk | Mexico
Concentration risk:
Concentration risk, number of employees	679
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk
Concentration risk:
Concentration risk, number of employees	1,247
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | International Association of Machinists and Aerospace Workers
Concentration risk:
Concentration risk, number of employees	246
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | Sindicato de Jorneleros y Obreros
Concentration risk:
Concentration risk, number of employees	583

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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=64851502&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=73719730&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=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

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