Property Dispositions (Notes)	9 Months Ended
Sep. 30, 2016
Property Dispositions [Abstract]
Property Acquisitions and Dispositions [Text Block]	On September 30, 2016, the Company sold non-strategic properties in North Dakota and Montana to a third party for cash proceeds of $214.8 million, with no gain or loss recognized. The sale included approximately 68,000 net acres of leasehold primarily in western Williams County, North Dakota, and approximately 12,000 net acres of leasehold in Roosevelt County, Montana. The sale also included producing properties with production totaling approximately 2,700 barrels of oil equivalent per day. The disposed properties represented an immaterial portion of the Company’s proved reserves. In April 2016, the Company sold approximately 132,000 net acres of undeveloped leasehold acreage located in Wyoming to a third party for cash proceeds of $110.0 million. In connection with the transaction, the Company recognized a pre-tax gain of $96.9 million. The disposed properties had no production or proved reserves. See Note 11. Subsequent Events for discussion of an asset disposition that closed subsequent to September 30, 2016. During the nine months ended September 30, 2015, the Company sold certain non-strategic properties in various areas to third parties for cash proceeds totaling $33.2 million. The proceeds primarily related to the assignment of certain non-producing leasehold acreage in Oklahoma to a third party for $25.9 million in May 2015. The Company recognized a pre-tax gain on that transaction of $20.5 million. The assigned properties represented an immaterial portion of the Company’s total acreage.

On September 30, 2016, the Company sold non-strategic properties in North Dakota and Montana to a third party for cash proceeds of $214.8 million, with no gain or loss recognized. The sale included approximately 68,000 net acres of leasehold primarily in western Williams County, North Dakota, and approximately 12,000 net acres of leasehold in Roosevelt County, Montana. The sale also included producing properties with production totaling approximately 2,700 barrels of oil equivalent per day. The disposed properties represented an immaterial portion of the Company’s proved reserves.

In April 2016, the Company sold approximately 132,000 net acres of undeveloped leasehold acreage located in Wyoming to a third party for cash proceeds of $110.0 million. In connection with the transaction, the Company recognized a pre-tax gain of $96.9 million. The disposed properties had no production or proved reserves.

See Note 11. Subsequent Events for discussion of an asset disposition that closed subsequent to September 30, 2016.

During the nine months ended September 30, 2015, the Company sold certain non-strategic properties in various areas to third parties for cash proceeds totaling $33.2 million. The proceeds primarily related to the assignment of certain non-producing leasehold acreage in Oklahoma to a third party for $25.9 million in May 2015. The Company recognized a pre-tax gain on that transaction of $20.5 million. The assigned properties represented an immaterial portion of the Company’s total acreage.