Net Income (Loss) Per Common Share - Net Income (Loss) Per Common Share on Basic and Diluted Basis (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net income (loss)	$ (46.9)	$ (48.8)	$ (78.5)	$ (66.0)
Less: Preferred share dividends	2.6	2.6	7.9	7.9
Net income (loss) attributable to common shareholders	(49.5)	(51.4)	(86.4)	(73.9)
Net income (loss) attributable to common shareholders	$ (49.5)	$ (51.4)	$ (86.4)	$ (73.9)
Weighted average common shares outstanding - basic (in shares)	35,197,824	35,014,182	35,158,416	34,955,787
Effect of dilutive securities:
Equity compensation awards (in shares)	0	0	0	0
Weighted average common shares outstanding - diluted (in shares)	35,197,824	35,014,182	35,158,416	34,955,787
Net income (loss) per common share:
Basic (in dollars per share)	$ (1.41)	$ (1.47)	$ (2.46)	$ (2.11)
Diluted (in dollars per share)	$ (1.41)	$ (1.47)	$ (2.46)	$ (2.11)