Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net income	$ 29.1	$ 28.0
Denominator — Weighted-average common shares outstanding (in thousands):
Basic (shares)	15,838	16,108
Add: dilutive effect of non-vested common shares, restricted stock units, performance shares and stock options (shares)	170	264
Diluted (shares)	16,008	16,372
Net income per common share:
Basic (in dollars per share)	$ 1.83	$ 1.74
Earnings per common share, Diluted:
Diluted (in dollars per share)	$ 1.81	$ 1.71