Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Basic and Diluted Earnings per share
Weighted average basic common shares outstanding (in shares)	17,763,451	17,797,318
Dilutive effect of employee stock purchases, net of assumed repurchase of treasury stock (in shares)	44,810	52,016
Weighted average dilutive common shares (in shares)	17,808,261	17,849,334
Basic:
Net income (loss)	$ 29.8	$ 38.6	$ 38.6
Less: Earnings (loss) allocated to participating securities	1.1	1.5
Net income (loss) available to basic common shares	$ 28.7	$ 37.2
Basic earnings (loss) per common share (in dollars per share)	$ 1.62	$ 2.09
Diluted:
Net income (loss)	$ 29.8	$ 38.6	$ 38.6
Less: Earnings (loss) allocated to participating securities	1.1	1.5
Net income (loss) available to diluted common shares	$ 28.7	$ 37.2
Diluted earnings (loss) per common share (in dollars per share)	$ 1.61	$ 2.08