Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 16.3	$ 10.9	$ 16.2	$ 15.9	$ 27.2	$ 32.1
Other comprehensive expense	(0.9)	$ 0.2	(0.2)		(0.7)	(0.6)
Comprehensive income	15.4		16.0		26.5	31.5
Less: Comprehensive income attributable to noncontrolling interest	1.1		0.9		1.4	1.5
Comprehensive income attributable to SP Plus Corporation	$ 14.3		$ 15.1		$ 25.1	$ 30.0