Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 56.4	$ 44.5	$ 26.0
Other comprehensive (loss) income	(0.6)	0.2	(0.3)
Comprehensive income	55.8	44.7	25.7
Less: Comprehensive income attributable to noncontrolling interest	3.2	3.3	2.9
Comprehensive income attributable to SP Plus Corporation	$ 52.6	$ 41.4	$ 22.8