Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (172.9)	$ 51.7	$ 56.4
Change in fair value of interest rate collars	(1.8)	(0.4)
Foreign currency translation gain (loss)	0.1	0.1	(0.6)
Comprehensive (loss) income	(174.6)	51.4	55.8
Less: Comprehensive (loss) income attributable to noncontrolling interest	(0.1)	2.9	3.2
Comprehensive (loss) income attributable to SP Plus Corporation	$ (174.5)	$ 48.5	$ 52.6