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, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net income (loss) attributable to SP Plus Corporation	$ 45.2	$ 31.7	$ (172.8)
Basic weighted average common shares outstanding	20,809,363	21,166,323	21,056,061
Dilutive impact of share-based awards	197,705	213,660
Diluted weighted average common shares outstanding	21,007,068	21,379,983	21,056,061
Net income (loss) per common share
Basic (in dollars per share)	$ 2.17	$ 1.50	$ (8.21)
Diluted (in dollars per share)	$ 2.15	$ 1.48	$ (8.21)