Acquisition - Pro Forma Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Combinations [Abstract]
Total services revenue	$ 418.6	$ 407.2	$ 1,242.2	$ 1,215.0
Net income attributable to SP Plus Corporation	$ 14.2	$ 13.6	$ 40.0	$ 44.7