Subsequent Event (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Purchase price to acquire oil and gas property	$ 48,300,000	$ 94,500,000
Williston Basin Divestiture [Member]
Subsequent Event [Line Items]
Purchase price to acquire oil and gas property	1,725,000,000
Cash Payments to Acquire Oil and Gas Property	1,650,000,000
Net book value of assets	2,521,800,000
Williston Basin Divestiture [Member] | Threshold 1 [Member]
Subsequent Event [Line Items]
Contractual Rights	50,000,000
Buyer's Share Price	12.00
Williston Basin Divestiture [Member] | Threshold 2 [Member]
Subsequent Event [Line Items]
Contractual Rights	25,000,000
Buyer's Share Price	$ 15.00