Fair Value Measurements (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Natural Gas Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	$ 7.5	$ 7.2
Derivative Liability	1.0	1.3
Natural Gas Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.4	0.3
Derivative Liability	5.3	0.3
Oil Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	6.9
Derivative Liability		5.2
Natural Gas Liquid Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	4.7	0.1
Derivative Liability	0.2	0.9
Oil Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Liability		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
Derivative Liability		0.0
Fair Value, Inputs, Level 1 [Member] | Natural Gas Liquid 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
Fair Value, Inputs, Level 2 [Member] | Natural Gas Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	7.5	7.2
Derivative Liability	1.0	1.3
Fair Value, Inputs, Level 2 [Member] | Natural Gas Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	0.4	0.3
Derivative Liability	5.3	0.3
Fair Value, Inputs, Level 2 [Member] | Oil Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	6.9
Derivative Liability		5.2
Fair Value, Inputs, Level 2 [Member] | Natural Gas Liquid Derivative [Member]
Debt Instrument [Line Items]
Derivative Asset	4.7	0.1
Derivative Liability	0.2	0.9
Fair Value, Inputs, Level 2 [Member] | Oil Basis Derivative [Member]
Debt Instrument [Line Items]
Derivative Liability		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
Derivative Liability		0.0
Fair Value, Inputs, Level 3 [Member] | Natural Gas Liquid 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