Earnings per Share ("EPS") - Schedule of Earnings Per Share Calculations, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings per basic common share
Income from continuing operations	$ 15.6	$ 14.4	$ 13.6	$ 11.8	$ 12.9	$ 12.9	$ (4.8)	$ 16.2	$ 55.4	$ 37.2	$ 80.3
Amounts attributable to participating securities									(0.3)	(0.2)	(0.6)
Income from continuing operations available to common stockholders									55.1	37.0	79.7
Loss from discontinued operations, net of income taxes									0.0	(0.8)	0.0
Amounts attributable to participating securities									0.0	0.0	0.0
Net income available to common stockholders									$ 55.1	$ 36.2	$ 79.7
Weighted-average basic shares outstanding (in shares)									16,848	16,850	16,805
Continuing operations (in dollars per share)	$ 0.92	$ 0.85	$ 0.80	$ 0.70	$ 0.77	$ 0.76	$ (0.29)	$ 0.96	$ 3.27	$ 2.20	$ 4.74
Discontinued operations (in dollars per share)									0	(0.05)	0
Basic (in dollars per share)									$ 3.27	$ 2.15	$ 4.74
Earnings per diluted common share
Income from continuing operations	$ 15.6	$ 14.4	$ 13.6	$ 11.8	$ 12.9	$ 12.9	$ (4.8)	$ 16.2	$ 55.4	$ 37.2	$ 80.3
Amounts attributable to participating securities									(0.3)	(0.4)	(0.5)
Income from continuing operations available to common stockholders									55.1	36.8	79.8
Loss from discontinued operations, net of income taxes									0.0	(0.8)	0.0
Amounts attributable to participating securities									0.0	0.0	0.0
Net income available to common stockholders									$ 55.1	$ 36.0	$ 79.8
Weighted-average basic shares outstanding (in shares)									16,848	16,850	16,805
Assumed incremental shares under stock-based compensation plans (in shares)									58	118	247
Weighted average diluted shares (in shares)									16,906	16,968	17,052
Continuing operations (in dollars per share)	$ 0.92	$ 0.84	$ 0.80	$ 0.69	$ 0.76	$ 0.75	$ (0.29)	$ 0.95	$ 3.26	$ 2.17	$ 4.68
Discontinued operations (in dollars per share)									0	(0.05)	0
Diluted (in dollars per share)									$ 3.26	$ 2.12	$ 4.68