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Commitments and Contingencies - Additional Information (Details) - 6 months ended Jun. 30, 2016 $ in Millions | USD ($) | MBbls | MMcf
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Commitments And Contingencies [Line Items] |  |  |
Total rental commitments under leases | $ 22.6 |  |
Future obligations under purchase agreements | $ 38.8 |  |
Williston Basin Project [Member] | Long Term Commitments [Member] |  |  |
Commitments And Contingencies [Line Items] |  |  |
Maximum commitment term (less than) | 10 years |  |
Future obligations under supply agreements | $ 442.0 |  |
Williston Basin Project [Member] | Crude oil [Member] | Long Term Commitments [Member] |  |  |
Commitments And Contingencies [Line Items] |  |  |
Minimum quantity of delivery (in MBbl of crude oil, MBbl of natural gas liquids, and MMcf of natural gas) | MBbls |  | 30,500 |
Williston Basin Project [Member] | Natural Gas [Member] | Long Term Commitments [Member] |  |  |
Commitments And Contingencies [Line Items] |  |  |
Minimum quantity of delivery (in MBbl of crude oil, MBbl of natural gas liquids, and MMcf of natural gas) |  | 23,000 | 220,600

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- Definition Total amount of product committed to be supplied under existing contracts or agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1207 -Paragraph (a) -Subparagraph (2) + Details
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- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
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