Divestitures, Assets Held for Sale, and Acquisitions Acquisitions (Details) $ in Thousands		3 Months Ended
	Apr. 19, 2018 USD ($) a	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Business Acquisition [Line Items]
Payments to Acquire Oil and Gas Property and Equipment		$ 0	$ 75,105
Subsequent Event [Member] | Other Martin County Acquisition 2018 [Member]
Business Acquisition [Line Items]
Net Acreage Acquired | a	760
Payments to Acquire Oil and Gas Property and Equipment	$ 24,600