Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share, Basic and Diluted [Line Items]
Net income	$ 36.7	$ 37.9	$ 66.0	$ 79.5
Weighted average common shares outstanding for basic earnings per share computation (in shares)	64,004,455	64,504,546	64,397,320	62,419,442
Dilutive effects of stock-based compensation (in shares)	78,034	202,913	116,566	248,949
Weighted average common shares outstanding for diluted earnings per common share computation (in shares)	64,082,489	64,707,459	64,513,886	62,668,391
Basic earnings per common share (in dollars per share)	$ 0.57	$ 0.59	$ 1.02	$ 1.27
Diluted earnings per common share (in dollars per share)	$ 0.57	$ 0.59	$ 1.02	$ 1.27
Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock (in shares)	108,369	761	108,369	108,046
Unvested restricted stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock (in shares)			296,188	147,415