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Multiemployer plan (Details 2) - Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member] - USD ($) $ in Millions | 3 Months Ended |
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Mar. 31, 2015 | Mar. 31, 2016
Multiemployer plans, pension [Member] |  |
Multiemployer Plans [Line Items] |  |
Additional multiemployer plan withdrawal obligation | $ 2.4 |
Multiemployer Plans, Pension [Member] |  |
Multiemployer Plans [Line Items] |  |
Multiemployer plans, withdrawal obligation |  | $ 16.4

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- Definition Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References No definition available. + Details
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- Details
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