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Subsequent Events - Additional Information (Detail) (USD $) | 9 Months Ended |  |  |  | 1 Months Ended |  | 1 Months Ended | 0 Months Ended
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Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 Drilling contracts [Member] | Sep. 30, 2013 Second Amended Credit Facility [Member] | Apr. 05, 2013 Second Amended Credit Facility [Member] | Mar. 31, 2013 Second Amended Credit Facility [Member] | Sep. 30, 2013 West Williston Acquisition [Member] | Oct. 10, 2013 Subsequent Event [Member] | Oct. 31, 2013 Subsequent Event [Member] Drilling contracts [Member] | Oct. 02, 2013 Subsequent Event [Member] Second Amended Credit Facility [Member] | Oct. 02, 2013 Subsequent Event [Member] West Williston Acquisition [Member] acre
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Acres acquired |  |  |  |  |  |  |  |  |  |  | 136,000
Acquisition, consideration transferred |  |  |  |  |  |  |  |  |  |  | $ 1,478,600,000
Acquisition, consideration transferred, deposit |  |  |  |  |  |  | 72,500,000 |  |  |  |
Proceeds from credit facility | 160,000,000 | 0 |  |  |  |  |  |  |  | 440,000,000 |
Line of credit facility, amount outstanding |  |  |  | 160,000,000 |  |  |  |  |  | 605,200,000 |
Line of credit facility, remaining borrowing capacity |  |  |  | 1,334,800,000 |  |  |  |  |  | 894,800,000 |
Line of credit facility, maximum borrowing capacity |  |  |  |  | 1,250,000,000 | 750,000,000 |  |  |  | 1,500,000,000 |
Payments upon early contract termination |  |  | 24,900,000 |  |  |  |  |  | 9,700,000 |  |
Purchase Commitment, Remaining Minimum Amount Committed |  |  |  |  |  |  |  | $ 3,600,000 |  |  |

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- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e6927-128479 + Details
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