Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share, Basic and Diluted [Line Items]
Net income	$ 51.4	$ 29.3
Weighted average common shares outstanding for basic earnings per share computation (in shares)	61,591,877	64,790,186
Dilutive effects of stock-based compensation (in shares)	122,186	146,921
Weighted average common shares outstanding for diluted earnings per common share computation (in shares)	61,714,063	64,937,107
Basic earnings per common share (in dollars per share)	$ 0.83	$ 0.45
Diluted earnings per common share (in dollars per share)	$ 0.83	$ 0.45
Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock (in shares)	92,602	113,468
Unvested restricted stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock (in shares)	368,793	309,410