Commitments and contingencies (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2016 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Commitments and Contingencies Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Unrecorded Unconditional Purchase Obligations Disclosure | Based on current prices, our estimated minimum purchase obligations under our CO2 contract is as follows:
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| Schedule of Future Minimum Rental Payments for Operating Leases | As of December 31, 2016, total remaining payments associated with our operating leases were:
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