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Supplier Concentration - Additional Information (Detail) - Supplier Concentration Risk - Vendor | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Concentration Risk [Line Items] |  |  |
Number of key suppliers | 10 |  |
Cost of Goods, Total |  |  |
Concentration Risk [Line Items] |  |  |
Percentage of purchases from key suppliers | 85.00% | 84.00% | 82.00%
Carrier and Its Affiliates | Cost of Goods, Total |  |  |
Concentration Risk [Line Items] |  |  |
Percentage of purchases from key suppliers | 62.00% | 62.00% | 61.00%

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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=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 + Details
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