Net Income Per Share (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator (basic and diluted):
Net income	$ 22.5	$ 17.4
Less: Dividends paid to participating securities	(0.3)	(0.1)
Undistributed and distributed earnings available to common stockholders	$ 22.2	$ 17.3
Denominator:
Average number of common shares outstanding (in shares)	30,712,300	30,620,600
Effect of dilutive stock-based compensation (in shares)	197,700	96,100
Average number of common and potential common shares outstanding (in shares)	30,910,000.0	30,716,700