Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (88.3)	$ 15.0	$ (173.7)	$ 42.2
Change in fair value of interest rate collars	0.4	(0.1)	(2.2)	(0.9)
Foreign currency translation loss		(0.1)	(0.3)
Comprehensive (loss) income	(87.9)	14.8	(176.2)	41.3
Less: Comprehensive (loss) income attributable to noncontrolling interest	(0.2)	0.8	(0.4)	2.2
Comprehensive (loss) income attributable to SP Plus Corporation	$ (87.7)	$ 14.0	$ (175.8)	$ 39.1