Fair Value Measurements (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Natural Gas Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	$ 1.5	$ 11.7
Derivative Liability	4.0	0.2
Natural Gas Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	1.1	3.4
Derivative Liability	0.4	0.9
Oil Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	2.5	1.6
Derivative Liability	5.9	7.0
Oil Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Liability	0.8	0.1
Fair Value, Inputs, Level 1 [Member] | Natural Gas Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Natural Gas Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Oil Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Oil Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Natural Gas Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	1.5	11.7
Derivative Liability	4.0	0.2
Fair Value, Inputs, Level 2 [Member] | Natural Gas Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	1.1	3.4
Derivative Liability	0.4	0.9
Fair Value, Inputs, Level 2 [Member] | Oil Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	2.5	1.6
Derivative Liability	5.9	7.0
Fair Value, Inputs, Level 2 [Member] | Oil Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Liability	0.8	0.1
Fair Value, Inputs, Level 3 [Member] | Natural Gas Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Natural Gas Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Oil Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.0	0.0
Derivative Liability	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Oil Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Liability	$ 0.0	$ 0.0