Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 15.0	$ 16.3	$ 10.9	$ 14.5	$ 16.2	$ 15.9	$ 42.2	$ 46.6
Other comprehensive income (expense)	(0.2)		$ 0.2	0.1			(0.9)	(0.4)
Comprehensive income	14.8			14.6			41.3	46.2
Less: Comprehensive income attributable to noncontrolling interest	0.8			1.0			2.2	2.5
Comprehensive income attributable to SP Plus Corporation	$ 14.0			$ 13.6			$ 39.1	$ 43.7