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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Basic
Income from continuing operations	$ 16.4	$ 16.4	$ 21.4	$ 19.2	$ 14.5	$ 13.5	$ 16.4	$ 16.1	$ 73.4	$ 60.5	$ 68.0
Amounts attributable to participating securities									(0.7)	(0.6)	(0.8)
Income from continuing operations available to common stockholders									72.7	59.9	67.2
Income (loss) from discontinued operations, net of income taxes									(0.4)	(9.4)	0.7
Amounts attributable to participating securities									0.0	0.1	0.0
Net income available to common stockholders									$ 72.3	$ 50.6	$ 67.9
Weighted-average basic shares outstanding (in shares)									16,773	16,754	16,584
Continuing operations (in dollars per share)	$ 0.97	$ 0.97	$ 1.26	$ 1.13	$ 0.86	$ 0.79	$ 0.97	$ 0.95	$ 4.33	$ 3.58	$ 4.05
Discontinued operations (in dollars per share)									(0.02)	(0.56)	0.04
Basic (in dollars per share)									$ 4.31	$ 3.02	$ 4.09
Diluted
Amounts attributable to participating securities									$ (0.6)	$ (0.5)	$ (0.8)
Income from continuing operations available to common stockholders									72.8	60.0	67.2
Amounts attributable to participating securities									0.0	0.1	0.0
Net income available to common stockholders									$ 72.4	$ 50.7	$ 67.9
Add: Assumed incremental shares under stock-based compensation plans (shares)									314	258	288
Weighted average diluted shares (in shares)									17,087	17,012	16,872
Continuing operations (in dollars per share)	$ 0.95	$ 0.95	$ 1.24	$ 1.11	$ 0.85	$ 0.78	$ 0.96	$ 0.94	$ 4.26	$ 3.53	$ 3.99
Discontinued operations (in dollars per share)									(0.02)	(0.55)	0.04
Diluted (in dollars per share)									$ 4.24	$ 2.98	$ 4.03