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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to SP Plus Corporation	$ 6.5	$ 9.8	$ 6.5	$ 11.1
Basic weighted average common shares outstanding (in shares)	22,344,898	22,145,190	22,336,693	22,136,458
Dilutive impact of share-based awards (in shares)	300,000	400,000	300,000	400,000
Diluted weighted average common shares outstanding (in shares)	22,625,471	22,521,832	22,609,443	22,505,403
Net income per common share
Basic (in dollars per share)	$ 0.29	$ 0.44	$ 0.29	$ 0.50
Diluted (in dollars per share)	$ 0.29	$ 0.43	$ 0.29	$ 0.49