Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 14.5	$ 12.0	$ 46.6	$ 36.0
Other comprehensive income (expense)	0.1	0.1	(0.4)	0.2
Comprehensive income	14.6	12.1	46.2	36.2
Less: Comprehensive income attributable to noncontrolling interest	1.0	0.8	2.5	2.6
Comprehensive income attributable to SP Plus Corporation	$ 13.6	$ 11.3	$ 43.7	$ 33.6