Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (39.8)	$ 16.3	$ (85.4)	$ 27.2
Change in fair value of interest rate collars	0.2	(0.8)	(2.6)	(0.8)
Foreign currency translation (loss) gain	(0.1)	(0.1)	(0.3)	0.1
Comprehensive (loss) income	(39.7)	15.4	(88.3)	26.5
Less: Comprehensive (loss) income attributable to noncontrolling interest	(0.7)	1.1	(0.2)	1.4
Comprehensive (loss) income attributable to SP Plus Corporation	$ (39.0)	$ 14.3	$ (88.1)	$ 25.1