Fair Value Measurements - Quantitative Information About Level 3 Fair Value Measurements (Details) $ in Millions		3 Months Ended
		Mar. 31, 2017 USD ($) $ / MMBTU	Dec. 31, 2016 USD ($)
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative liabilities		$ 1.3	$ 0.1
Fair Value, Measurements, Recurring | Commodity
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative liabilities		1.3	0.1
Level 3 | Fair Value, Measurements, Recurring
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative liabilities		1.3
Level 3 | Fair Value, Measurements, Recurring | Commodity
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative liabilities		1.3	$ 0.0
Level 3 | Fair Value, Measurements, Recurring | Natural Gas | Commodity | Discounted cash flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative liabilities	[1]	$ 1.3
Level 3 | Fair Value, Measurements, Recurring | Natural Gas | Minimum | Commodity | Discounted cash flow | Derivative Financial Instruments, Liabilities
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair value inputs, price | $ / MMBTU	[2]	2.2
Level 3 | Fair Value, Measurements, Recurring | Natural Gas | Maximum | Commodity | Discounted cash flow | Derivative Financial Instruments, Liabilities
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair value inputs, price | $ / MMBTU	[2]	3.6
Level 3 | Fair Value, Measurements, Recurring | Natural Gas | Weighted Average | Commodity | Discounted cash flow | Derivative Financial Instruments, Liabilities
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair value inputs, price | $ / MMBTU	[3]	2.8

[1] Includes basis.

[2] Represents market prices beyond defined terms for Levels 1 and 2.

[3] Averages weighted by volume.