Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Schedule of assets and liabilities that are recognized at fair value on a recurring basis

The following table presents assets and liabilities included in our consolidated balance sheets that are recognized at fair value on a recurring basis, and indicates the fair value hierarchy utilized to determine such fair value as of September 30, 2017 and December 31, 2016:

	September 30, 2017
	Total			Quoted Market Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
	(in millions)
Cash equivalents	$	59.8		$	59.8	$	—		$	—
Unrealized gains on natural gas derivatives	0.2			—		0.2			—
Total assets at fair value	$	60.0		$	59.8	$	0.2		$	—
Unrealized losses on natural gas derivatives	$	(2.6	)	$	—	$	(2.6	)	$	—
Total liabilities at fair value	$	(2.6	)	$	—	$	(2.6	)	$	—

	December 31, 2016
	Total			Quoted Market Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
	(in millions)
Cash equivalents	$	32.0		$	32.0	$	—		$	—
Unrealized gains on natural gas derivatives	9.0			—		9.0			—
Total assets at fair value	$	41.0		$	32.0	$	9.0		$	—
Unrealized losses on natural gas derivatives	$	(1.6	)	$	—	$	(1.6	)	$	—
Total liabilities at fair value	$	(1.6	)	$	—	$	(1.6	)	$	—