Net Income per Common Share Net Income per Common Share - Weighted Average Common Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to SP Plus Corporation	$ 7.0	$ 3.7	$ 13.5	$ 14.8
Basic weighted average common shares outstanding (in shares)	22,208,139	22,205,707	22,293,776	22,159,701
Dilutive impact of share-based awards (in shares)	288,972	342,459	278,157	360,117
Diluted weighted average common shares outstanding (in shares)	22,497,111	22,548,166	22,571,933	22,519,818
Net income per common share
Basic (in dollars per share)	$ 0.31	$ 0.17	$ 0.60	$ 0.67
Diluted (in dollars per share)	$ 0.31	$ 0.16	$ 0.60	$ 0.66