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Subsequent Events (Details) $ / shares in Units, a in Thousands |  |  | 2 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 21, 2016 USD ($) $ / shares shares | Oct. 17, 2016 a | Dec. 01, 2016 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Oct. 31, 2016 MMBTU | Oct. 31, 2016 MBbls | Oct. 31, 2016 $ / bbl | Oct. 31, 2016 $ / MMBTU | Oct. 14, 2016 USD ($) | Feb. 23, 2016 USD ($) | Feb. 22, 2016 USD ($) | Feb. 02, 2016 $ / shares
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued, price per share (in usd per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 4.685
Net proceeds from offering |  |  |  | $ 182,791,000 | $ 462,833,000 |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, current borrowing capacity |  |  |  |  |  |  |  |  |  |  | $ 1,150,000,000.0 | $ 1,525,000,000.0 |
Subsequent Event [Member] | Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock (in shares) | shares | 55,200,000 |  |  |  |  |  |  |  |  |  |  |  |
Shares issued, price per share (in usd per share) | $ / shares | $ 10.80 |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from offering | $ 584,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Over-Allotment Option [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock (in shares) | shares | 7,200,000 |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Williston Basin Acquisition [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Acres acquired | a |  | 55 |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Revolving Credit Facility [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, current borrowing capacity |  |  |  |  |  |  |  |  |  | $ 1,150,000,000.0 |  |  |
Subsequent Event [Member] | Commodity derivative instruments [Member] | Commodity Contract Maturing in 2017 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total notional amount |  |  |  |  |  | 668,000 | 2,338 |  |  |  |  |  |
Subsequent Event [Member] | Commodity derivative instruments [Member] | Commodity Contract Maturing in 2018 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total notional amount |  |  |  |  |  | 62,000 | 1,219 |  |  |  |  |  |
Subsequent Event [Member] | Commodity derivative instruments [Member] | Commodity Contract Maturing in 2019 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Total notional amount | MBbls |  |  |  |  |  |  | 93 |  |  |  |  |  |
Subsequent Event [Member] | Crude oil [Member] | Commodity derivative instruments [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average floor price (in dollars per barrel) | $ / bbl |  |  |  |  |  |  |  | 51.73 |  |  |  |  |
Subsequent Event [Member] | Natural Gas [Member] | Commodity derivative instruments [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average floor price (in dollars per barrel) | $ / MMBTU |  |  |  |  |  |  |  |  | 3.38 |  |  |  |
Scenario, Forecast [Member] | Williston Basin Acquisition [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration to be paid for Purchase Agreement |  |  | $ 785,000,000 |  |  |  |  |  |  |  |  |  |

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