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
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net income (loss)	$ (1.0)	$ 29.8
Less: Preferred share dividends	2.6	2.6
Net income (loss) attributable to common shareholders	(3.6)	27.2
Net income (loss) attributable to common shareholders	$ (3.6)	$ 27.2
Weighted average common shares outstanding - basic (in shares)	34,891,935	34,712,650
Effect of dilutive securities:
Equity compensation awards (in shares)	0	225,363
Weighted average common shares outstanding - diluted (in shares)	34,891,935	34,938,013
Net income (loss) per common share:
Basic (in dollars per share)	$ (0.11)	$ 0.78
Diluted (in dollars per share)	$ (0.11)	$ 0.78