Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Basic and Diluted [Line Items]
Net income	$ 48.3	$ 49.1	$ 114.3	$ 128.6
Weighted average common shares outstanding for basic earnings per share computation (in shares)	63,764,474	64,832,324	64,184,832	63,232,575
Dilutive effects of stock-based compensation (in shares)	96,983	211,162	110,693	238,708
Weighted average common shares outstanding for diluted earnings per common share computation (in shares)	63,861,457	65,043,486	64,295,525	63,471,283
Basic earnings per common share (in dollars per share)	$ 0.76	$ 0.76	$ 1.78	$ 2.03
Diluted earnings per common share (in dollars per share)	$ 0.76	$ 0.76	$ 1.78	$ 2.03
Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock (in shares)	68,397	4,808	73,633	5,569
Unvested restricted stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock (in shares)			293,236	143,415