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INTANGIBLE ASSETS | 12 Months Ended
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Dec. 31, 2013
Finite-Lived Intangible Assets, Net [Abstract] |
Intangible Assets | INTANGIBLE ASSETS Intangible assets consisted of the following:
| December 31, 2013 |  | December 31, 2012
| Cost |  | Accumulated Amortization |  | Cost |  | Accumulated Amortization
| (Thousands of Dollars)
Customer relationships | $ | 127,614 |  |  | $ | (58,230 | ) |  | $ | 137,470 |  |  | $ | (46,951 | )
Other | 2,359 |  |  | (494 | ) |  | 2,359 |  |  | (443 | )
Total | $ | 129,973 |  |  | $ | (58,724 | ) |  | $ | 139,829 |  |  | $ | (47,394 | )
All of our intangible assets are subject to amortization. Amortization expense for intangible assets was $13.8 million, $7.8 million and $8.3 million for the years ended December 31, 2013, 2012 and 2011, respectively. The estimated aggregate amortization expense for the next five years is as follows:
| Amortization Expense
| (Thousands of Dollars)
2014 | $ | 12,579 |
2015 | $ | 9,709 |
2016 | $ | 6,840 |
2017 | $ | 6,840 |
2018 | $ | 6,840 |

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- Definition The entire disclosure for all or part of the information related to intangible assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16373-109275 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275 + Details
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