Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Statement of Financial Position [Abstract]
Intangible assets, accumulated amortization	$ 4.6	$ 4.0	$ 3.4	$ 2.9	$ 15.9	$ 16.9	$ 16.3	$ 15.8
Intangible liabilities, accumulated amortization	$ 10.8	$ 10.6	$ 10.3	$ 10.0	$ 9.8	$ 14.3	$ 14.0	$ 13.8
Common stock, par value (in USD per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 2.50
Common stock, shares authorized	30,000,000	30,000,000	30,000,000	30,000,000	30,000,000	30,000,000	30,000,000	30,000,000
Common stock, shares issued		18,570,642	18,569,845	18,402,961	18,162,148	18,021,061	17,952,320	17,769,746
Common stock, shares outstanding		18,570,642	18,569,845	18,402,961	18,162,148	18,021,061	17,952,320	17,769,746