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Summary of Significant Accounting Policies - Concentration Risk (Details) | 12 Months Ended
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Dec. 31, 2012 Customer | Dec. 31, 2011 Customer
Customer concentration risk |  |
Concentration risk: |  |
Number of major customers | 2 | 2
Accounts receivable | Customer concentration risk |  |
Concentration risk: |  |
Concentration risk percentage | 75.00% | 77.00%
Sales | Customer concentration risk |  |
Concentration risk: |  |
Concentration risk percentage | 74.00% | 80.00%
Sales | Geographic concentration risk | Mexico and Canada |  |
Concentration risk: |  |
Concentration risk percentage | 28.00% | 24.00%
Number of employees, geographic area | Labor force concentration risk |  |
Concentration risk: |  |
Concentration risk, number of employees | 1,373 |
Number of employees, geographic area | Labor force concentration risk | Mexico |  |
Concentration risk: |  |
Concentration risk, number of employees | 867 |
Number of employees, geographic area | Labor force concentration risk | United States |  |
Concentration risk: |  |
Concentration risk, number of employees | 506 |
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk |  |
Concentration risk: |  |
Concentration risk, number of employees | 1,373 |
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | International Association of Machinists and Aerospace Workers |  |
Concentration risk: |  |
Concentration risk, number of employees | 154 |
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | Sindicato de Jorneleros y Obreros |  |
Concentration risk: |  |
Concentration risk, number of employees | 764 |

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- Definition Concentration Risk, Number of Significant Customers + References No definition available. + Details
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References 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=6927468&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 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611 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=6927468&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 20 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611 + Details
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