Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 17.3	$ 7.4	$ 24.0	$ 8.0
Effective portion of unrealized loss on cash flow hedge	0.0	(0.1)	0.0	(0.3)
Foreign currency translation gain (loss)	0.1	(0.1)	0.1	0.0
Comprehensive income	17.4	7.2	24.1	7.7
Less: Comprehensive income attributable to noncontrolling interest	1.1	0.9	1.8	1.5
Comprehensive income attributable to SP Plus Corporation	$ 16.3	$ 6.3	$ 22.3	$ 6.2