Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of Significant Accounting Policies
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									45,000	15,000	450,000
Earnings per basic common share
Income from continuing operations	$ 14.5	$ 13.5	$ 16.4	$ 16.1	$ 27.2	$ 13.4	$ 15.0	$ 12.4	$ 60.5	$ 68.0	$ 48.5
Distributed and undistributed amounts allocated to participating securities									(0.6)	(0.8)	(0.8)
Income from continuing operations available to common stockholders									59.9	67.2	47.7
Income (loss) from discontinued operations, net of income taxes									(9.4)	0.7	3.5
Distributed and undistributed amounts allocated to participating securities									(0.1)
Net income available to common stockholders									$ 50.6	$ 67.9	$ 51.2
Weighted-average basic shares outstanding									16,754,000	16,584,000	16,072,000
Basic earnings (loss) per share
Continuing operations	$ 0.86	$ 0.79	$ 0.97	$ 0.95	$ 1.61	$ 0.79	$ 0.89	$ 0.75	$ 3.58	$ 4.05	$ 2.97
Discontinued operations									(0.56)	0.04	0.21
Basic (in dollars per share)									$ 3.02	$ 4.09	$ 3.18
Earnings per diluted common share
Income from continuing operations	$ 14.5	$ 13.5	$ 16.4	$ 16.1	$ 27.2	$ 13.4	$ 15.0	$ 12.4	$ 60.5	$ 68.0	$ 48.5
Distributed and undistributed amounts allocated to participating securities									(0.5)	(0.8)	(0.8)
Income from continuing operations available to common stockholders									60.0	67.2	47.7
Income (loss) from discontinued operations, net of income taxes									(9.4)	0.7	3.5
Distributed and undistributed amounts allocated to participating securities									0.1
Net income available to common stockholders									$ 50.7	$ 67.9	$ 51.2
Weighted-average basic shares outstanding									16,754,000	16,584,000	16,072,000
Add: Assumed incremental shares under stock-based compensation plans									258,000	288,000	331,000
Weighted average diluted shares									17,012,000	16,872,000	16,403,000
Diluted earnings (loss) per share
Continuing operations	$ 0.85	$ 0.78	$ 0.96	$ 0.94	$ 1.59	$ 0.78	$ 0.88	$ 0.74	$ 3.53	$ 3.99	$ 2.91
Discontinued operations									(0.55)	0.04	0.21
Diluted (in dollars per share)									$ 2.98	$ 4.03	$ 3.12
Postretirement Benefits Other than Pensions
Cash and Cash Equivalents
Restricted cash and cash equivalent	$ 0.3				$ 0.4				$ 0.3	$ 0.4