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Commitments and Contingencies - Additional Information (Detail) $ in Thousands |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Jul. 06, 2013 defendant | Sep. 30, 2015 USD ($) MBbls MMcf | Sep. 30, 2014 USD ($) | Sep. 30, 2015 USD ($) MBbls MMcf | Sep. 30, 2014 USD ($) | Oct. 01, 2015 USD ($)
Commitments And Contingencies [Line Items] |  |  |  |  |  |
Total rental commitments under leases |  | $ 28,700 |  | $ 28,700 |  |
Rig termination |  | 0 | $ 0 | 3,895 | $ 0 |
Future obligations under purchase agreements |  |  |  | 38,600 |  |
Future obligations under cost sharing agreements |  |  |  | 2,300 |  |
Number of named defendants (over) | defendant | 50 |  |  |  |  |
Long Term Commitments [Member] |  |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |  |
Future obligations under supply agreements |  |  |  | 193,800 |  |
Drilling contracts [Member] |  |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |  |
Payments upon early contract termination |  | $ 5,300 |  | $ 5,300 |  | $ 7,100
Williston Basin Project [Member] | Long Term Commitments [Member] |  |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |  |
Maximum commitment term (less than) |  |  |  | 10 years |  |
Williston Basin Project [Member] | Long Term Commitments [Member] | Crude oil [Member] |  |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |  |
Minimum quantity of delivery | MBbls |  | 29,200 |  | 29,200 |  |
Williston Basin Project [Member] | Long Term Commitments [Member] | Natural Gas [Member] |  |  |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |  |  |
Minimum quantity of delivery | MMcf |  | 4,100 |  | 4,100 |  |

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