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Commitments and contingencies - Legal Contingencies (Details) - USD ($) |  | 12 Months Ended | 45 Months Ended
--- | --- | --- | ---
Feb. 09, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2016
Loss Contingencies [Line Items] |  |  |  |  |  |
Estimated litigation liability |  | $ 23,000,000 |  |  |  | $ 23,000,000
Pension contributions |  | 0 | $ 34,595,000 | $ 0 |  |
PBGC Agreement [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Required pension contributions above minimum |  |  |  |  |  | $ 17,400,000
Pension contributions |  | 0 | $ 1,100,000 | $ 0 | $ 6,700,000 |
Pension contributions above minimum remaining |  | $ 9,600,000 |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Litigation settlement amount | $ 23,000,000 |  |  |  |  |
Litigation settlement period | 10 years |  |  |  |  |
Litigation settlement payable upon final approval of settlement | $ 5,000,000 |  |  |  |  |
Litigation settlement, annual installment | $ 2,000,000 |  |  |  |  |
Litigation settlement installment period | 9 years |  |  |  |  |

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- Definition Litigation Settlement, Annual Installment + References No definition available. + Details
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- Definition Litigation Settlement Installment Period + References No definition available. + Details
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- Definition Litigation Settlement, Payable upon Final Approval of Settlement + References No definition available. + Details
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- Definition Litigation Settlement Period + References No definition available. + Details
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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, this amount represents the remaining additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
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- Definition Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.25) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The amount of cash or cash equivalents contributed by the entity to fund its pension plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3536-108585 + Details
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