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Income Taxes - Change in Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Change in unrecognized tax benefits |  |  |
Balance as of January 1 | $ 179,255 | $ 188,376 | $ 201,338
Additions based on tax positions related to the current year |  |  | 384
Additions for tax positions of prior years | 25,119 | 3,873 |
Reductions for tax positions of prior years | (171,171) | (11,547) | (9,234)
Settlements |  | (1,447) | (4,112)
Balance as of December 31 | 33,203 | 179,255 | 188,376
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation |  |  | 2,000
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations |  |  | 1,100
Additions based on tax positions related to the current year due to internal restructuring |  | 167,000 |
Reductions for tax positions for prior years due to expiration of statutes |  |  | 1,100
Interest and penalties on unrecognized tax benefits | 9,700 | 9,200 | 7,400
Liability related to unrecognized tax benefit for accrued interest and penalties | 500 | 600 | 1,400
Canada, Trinidad and U.S |  |  |
Change in unrecognized tax benefits |  |  |
Settlements |  |  | (6,000)
Colombia, Ecuador, Canada and Montana |  |  |
Change in unrecognized tax benefits |  |  |
Settlements |  |  | $ (5,000)
Australia Algeria And Mexico |  |  |
Change in unrecognized tax benefits |  |  |
Settlements |  | (2,000) |
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations |  | 7,200 |
Reductions for tax positions for prior years due to expiration of statutes |  | 7,200 |
Trinidad |  |  |
Change in unrecognized tax benefits |  |  |
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation |  | $ 2,100 |
Norway |  |  |
Change in unrecognized tax benefits |  |  |
Settlements | (12,000) |  |
U.S. Federal |  |  |
Change in unrecognized tax benefits |  |  |
Settlements | (9,000) |  |
Egypt |  |  |
Change in unrecognized tax benefits |  |  |
Settlements | $ (2,000) |  |

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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