Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 10.9	$ 15.9
Foreign currency translation	0.2	(0.4)
Comprehensive income	11.1	15.5
Less: Comprehensive income attributable to noncontrolling interest	0.3	0.6
Comprehensive income attributable to SP Plus Corporation	$ 10.8	$ 14.9