Net Income (Loss) per Common Share - Basic and Diluted Net (Loss) Income per Common Share and Weighted Average Common Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to SP Plus Corporation	$ 31.7	$ (172.8)	$ 48.8
Basic weighted average common shares outstanding	21,166,323	21,056,061	22,080,025
Dilutive impact of share-based awards	213,660		128,007
Diluted weighted average common shares outstanding	21,379,983	21,056,061	22,208,032
Net income (loss) per common share
Basic (in dollars per share)	$ 1.50	$ (8.21)	$ 2.21
Diluted (in dollars per share)	$ 1.48	$ (8.21)	$ 2.20