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Basis of presentation and summary of significant accounting policies (Details 2) (USD $) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012
Changes in accumulated other comprehensive loss by component |  |  |  |
Balance at beginning of period |  |  | $ 9,400,000 |
Other comprehensive loss: |  |  |  |
Foreign currency translation adjustments | (18,000,000) | (13,900,000) | (30,100,000) | 3,300,000
Net change from periodic revaluations | 100,000 | 200,000 | 400,000 | 500,000
Tax benefit | 600,000 | (5,300,000) | (1,900,000) | (22,200,000)
Total Other comprehensive income (loss) | (17,300,000) | (14,200,000) | (29,100,000) | 3,300,000
Balance at end of period | (19,500,000) |  | (19,500,000) |
Foreign currency translation |  |  |  |
Changes in accumulated other comprehensive loss by component |  |  |  |
Balance at beginning of period | 600,000 | 13,800,000 | 12,700,000 | (3,400,000)
Other comprehensive loss: |  |  |  |
Foreign currency translation adjustments | (18,000,000) | (13,900,000) | 30,100,000 | 3,300,000
Balance at end of period | (17,400,000) | (100,000) | (17,400,000) | (100,000)
Cash flow hedges |  |  |  |
Changes in accumulated other comprehensive loss by component |  |  |  |
Balance at beginning of period | (1,100,000) | (1,100,000) | (1,400,000) | (1,400,000)
Other comprehensive loss: |  |  |  |
Net change from periodic revaluations | 1,000,000 | (800,000) | 1,000,000 | (800,000)
Tax (expense) benefit | (400,000) | 300,000 | (400,000) | 300,000
Total Other comprehensive income (loss) before reclassifications, net of tax | 600,000 | (500,000) | 600,000 | (500,000)
Tax benefit | 200,000 | 100,000 | 200,000 | 300,000
Total amount reclassified from Accumulated other comprehensive loss, net of tax | 100,000 | 200,000 | 400,000 | 500,000
Total Other comprehensive income (loss) | 700,000 | (300,000) | 100,000 |
Balance at end of period | (400,000) | (1,400,000) | (400,000) | (1,400,000)
Cash flow hedges | Amount reclassified from accumulated other comprehensive income |  |  |  |
Other comprehensive loss: |  |  |  |
Net amount reclassified to earnings: | 300,000 | 300,000 | 600,000 | 800,000
Cash flow hedges | Amount reclassified from accumulated other comprehensive income | Interest rate swaps |  |  |  |
Other comprehensive loss: |  |  |  |
Net amount reclassified to earnings: | 400,000 | 300,000 | 800,000 | 800,000
Cash flow hedges | Amount reclassified from accumulated other comprehensive income | Fuel commodity swaps |  |  |  |
Other comprehensive loss: |  |  |  |
Net amount reclassified to earnings: | $ (100,000) |  | $ (200,000) |

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