Net Loss Per Share - Reconciliation of Numerator and Denominator of the Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net loss applicable to common shareholders	$ 15.5	$ (11.2)	$ (27.2)	$ (15.9)	$ (0.6)	$ (3.9)	$ (2.1)	$ (8.2)	$ (38.8)	$ (14.8)	$ (24.6)
Denominator:
Denominator for basic EPS–weighted-average common shares (in shares)									59,925,776	52,189,580	44,773,560
Dilutive effect of stock-based compensation arrangements (in shares)									0	0	0
Denominator for diluted EPS–adjusted weighted-average common shares (in shares)									59,925,776	52,189,580	44,773,560
Basic EPS (in dollars per share)	$ 0.23	$ (0.17)	$ (0.51)	$ (0.30)	$ (0.01)	$ (0.07)	$ (0.04)	$ (0.16)	$ (0.65)	$ (0.28)	$ (0.55)
Diluted EPS (in dollars per share)	$ 0.22	$ (0.17)	$ (0.51)	$ (0.30)	$ (0.01)	$ (0.07)	$ (0.04)	$ (0.16)	$ (0.65)	$ (0.28)	$ (0.55)