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Summary of Significant Accounting Policies - Concentration Risk (Details) | 12 Months Ended
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Dec. 31, 2015 Employee Customer | Dec. 31, 2014 | Dec. 31, 2013
Sales | Customer concentration risk |  |  |
Concentration risk: |  |  |
Number of major customers, Sales | Customer | 4 |  |
Concentration risk percentage | 82.00% | 87.00% | 86.00%
Sales | Geographic concentration risk | Mexico and Canada |  |  |
Concentration risk: |  |  |
Concentration risk percentage | 35.00% | 30.00% | 34.00%
Accounts receivable | Customer concentration risk |  |  |
Concentration risk: |  |  |
Concentration Risk, Accounts Receivable, Number of major customers | Customer | 4 |  |
Concentration risk percentage | 88.00% | 90.00% |
Number of employees, geographic area | Labor force concentration risk |  |  |
Concentration risk: |  |  |
Concentration risk, number of employees | 1,525 |  |
Number of employees, geographic area | Labor force concentration risk | United States |  |  |
Concentration risk: |  |  |
Concentration risk, number of employees | 685 |  |
Number of employees, geographic area | Labor force concentration risk | Mexico |  |  |
Concentration risk: |  |  |
Concentration risk, number of employees | 840 |  |
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk |  |  |
Concentration risk: |  |  |
Concentration risk, number of employees | 1,525 |  |
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | International Association of Machinists and Aerospace Workers |  |  |
Concentration risk: |  |  |
Concentration risk, number of employees | 293 |  |
Workforce subject to collective bargaining arrangements | Unionized employees concentration risk | Sindicato de Jorneleros y Obreros |  |  |
Concentration risk: |  |  |
Concentration risk, number of employees | 731 |  |

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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=51801978&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=49121117&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=51801978&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=49121117&loc=d3e13537-108611 + Details
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