Background and Basis of Presentation - EPS (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) primary_operations $ / shares shares	Mar. 31, 2017 USD ($) $ / shares shares
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of primary operations | primary_operations	2
Earnings (Loss) Per Basic Common Share
Income from continuing operations	$ 16.2	$ 17.6
Amounts attributable to participating securities	(0.1)	(0.1)
Income from continuing operations available to common stockholders	16.1	17.5
Loss from discontinued operations, net of income taxes	0.0	0.0
Net income available to common stockholders	$ 16.1	$ 17.5
Weighted-average basic shares outstanding (in shares) | shares	16,847,000	16,779,000
Basic earnings (loss) per share
Continuing operations (in dollars per share) | $ / shares	$ 0.96	$ 1.04
Discontinued operations (in dollars per share) | $ / shares	0.00	0.00
Basic earnings per share | $ / shares	$ 0.96	$ 1.04
Earnings (Loss) Per Diluted Common Share
Income from continuing operations	$ 16.2	$ 17.6
Amounts attributable to participating securities	(0.1)	(0.1)
Income from continuing operations available to common stockholders	16.1	17.5
Loss from discontinued operations, net of income taxes	0.0	0.0
Net income available to common stockholders	$ 16.1	$ 17.5
Weighted-average basic shares outstanding (in shares) | shares	16,847,000	16,779,000
Add: Assumed incremental shares under stock compensation plans (in shares) | shares	159,000	246,000
Weighted-average diluted shares (in shares) | shares	17,006,000	17,025,000
Diluted earnings (loss) per share
Continuing operations (in dollars per share) | $ / shares	$ 0.95	$ 1.03
Discontinued operations (in dollars per share) | $ / shares	0.00	0.00
Diluted (in dollars per share) | $ / shares	$ 0.95	$ 1.03
Potentially dilutive stock-based compensation awards excluded from computation of dilutive common shares (in shares) | shares	197,200	72,000