Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 3.9	$ (45.6)
Change in fair value of interest rate collars	0.4	(2.8)
Foreign currency translation loss		(0.2)
Comprehensive income (loss)	4.3	(48.6)
Less: Comprehensive income attributable to noncontrolling interest	1.6	0.5
Comprehensive income (loss) attributable to SP Plus Corporation	$ 2.7	$ (49.1)