Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) $ / MMBTU
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivatives assets	$ 1.6
Fair Value, Measurements, Recurring | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivatives assets	1.6
Fair Value, Measurements, Recurring | Level 3 | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivatives assets	1.6
Fair Value, Measurements, Recurring | Level 3 | Commodity | Discounted cash flow
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivatives assets	1.6
Fair Value, Measurements, Recurring | Level 3 | Natural Gas | Commodity | Discounted cash flow
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivatives assets	$ 1.6
Fair Value, Measurements, Recurring | Level 3 | Natural Gas | Commodity | Discounted cash flow | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market price (per Dth) | $ / MMBTU	2.6	[1]
Fair Value, Measurements, Recurring | Level 3 | Natural Gas | Commodity | Discounted cash flow | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market price (per Dth) | $ / MMBTU	3.6	[1]
Fair Value, Measurements, Recurring | Level 3 | Natural Gas | Commodity | Discounted cash flow | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market price (per Dth) | $ / MMBTU	3.1	[1],[2]

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

[2] Averages weighted by volume.