Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 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 March 31, 2017 and December 31, 2016:

	March 31, 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	$	40.1		$	40.1	$	—		$	—
Unrealized gains on natural gas derivatives	1.9			—		1.9			—
Total assets at fair value	$	42.0		$	40.1	$	1.9		$	—
Unrealized losses on natural gas derivatives	$	(2.5	)	$	—	$	(2.5	)	$	—
Total liabilities at fair value	$	(2.5	)	$	—	$	(2.5	)	$	—

	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	)	$	—