Earnings (Loss) Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Basic EPS:
Net income (loss)	$ 9.2	$ (5.2)	$ 0.2	$ (13.4)	$ (2.9)	$ (23.3)	$ 4.2	$ (39.6)
Less dividends on preferred shares	(5.3)			(4.8)			(15.4)	(14.2)
Less income allocated to preferred shareholders	(1.9)			0.0			0.0	0.0
Net income (loss) available/allocated to common shareholders - basic	2.0			(18.2)			(11.2)	(53.8)
Diluted EPS:
Less income allocated to preferred shareholders	(1.5)			0.0			0.0	0.0
Net income (loss) available/(allocated) to common shareholders - diluted	$ 2.4			$ (18.2)			$ (11.2)	$ (53.8)
Basic weighted-average common shares (in shares)	112,230,439			109,089,507			111,005,255	107,921,457
Add: Effect of dilutive equity awards (in shares)	10,465,800			0			0	0
Add: Effect of dilutive warrants (in shares)	42,926,168			0			0	0
Diluted weighted average common shares (in shares)	165,622,407			109,089,507			111,005,255	107,921,457
Net income (loss) per common share (basic) (in dollars per share)	$ 0.02			$ (0.17)			$ (0.10)	$ (0.50)
Net income (loss) per common share (diluted) (in dollars per share)	$ 0.01			$ (0.17)			$ (0.10)	$ (0.50)