Exhibit 12.1

COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES

(Dollars in millions, except ratio amounts)

	Nine Months Ended September 30,			Year Ended December 31,
	2017			2016			2015 Adjusted			2014 Adjusted		2013		2012
(Loss) income before income taxes	$	(8.7	)	$	(142.0	)	$	(71.7	)	$	68.7	$	127.6	$	234.3
Plus:
Fixed charges	12.4			13.4			5.5			8.9		12.0		5.8
Amortization of capitalized interest	1.3			1.9			1.7			0.7		0.6		0.6
Less:
Interest capitalized	0.5			0.7			1.0			6.9		10.8		4.5
Earnings (loss)	4.5			(127.4		)	(65.5		)	71.4		129.4		236.2
Interest (A)	10.3			10.6			3.9			7.1		11.0		4.8
Amortization of deferred financing costs	1.2			1.5			0.5			0.9		0.1		0.2
Interest portion of rental expense	0.9			1.3			1.1			0.9		0.9		0.8
Fixed Charges	$	12.4		$	13.4		$	5.5		$	8.9	$	12.0	$	5.8
Ratio of Earnings to Fixed Charges	0.36			(B)			(B)			8.02		10.78		40.72

(A) Amount includes interest expense on debt and capitalized interest during the period.

(B) For the year ended December 31, 2016, there was a deficiency of earnings to cover the fixed charges of $114.2 million. For the year ended December 31, 2015, there was a deficiency of earnings to cover the fixed charges of $60.0 million. Accordingly, the ratios for these periods have not been presented.