Commitments and Contingencies (Environmental Compliance) (Details) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2019 Release	Mar. 31, 2015 Release	Sep. 30, 2020 USD ($) miles	Dec. 31, 2019 USD ($) bbl	Sep. 15, 2015 USD ($)	May 31, 2015 bbl	Dec. 31, 2014 bbl
Site Contingency [Line Items]
Miles of Water Gathering Pipeline Removed | miles			30
Fort Berthold Indian Reservation
Site Contingency [Line Items]
Site Contingency, Loss Exposure, Number of Releases of Produced Water | Release	2	3
Site Contingency, Loss Exposure, Release of Produced Water | bbl				5,000		5,200	28,000
Accrual for Environmental Loss Contingencies			$ 3.6	$ 6.7
Maximum
Site Contingency [Line Items]
Loss Contingency, Estimate of Possible Loss					$ 1.1
Maximum | Fort Berthold Indian Reservation
Site Contingency [Line Items]
Site Contingency, Loss Exposure in Excess of Accrual, Best Estimate			$ 4.8