Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Parking services revenue
Lease contracts	$ 563.1	$ 545.0	$ 570.9
Management contracts	348.2	346.8	350.3
Total parking services revenue	911.3	891.8	921.2
Reimbursed management contract revenue	679.2	676.6	650.6
Total parking services revenue	1,590.5	1,568.4	1,571.8
Cost of parking services
Lease contracts	518.4	505.6	532.8
Management contracts	207.6	209.8	218.3
Total cost of parking services, gross	726.0	715.4	751.1
Reimbursed management contract expense	679.2	676.6	650.6
Total cost of parking services	1,405.2	1,392.0	1,401.7
Gross profit
Lease contracts	44.7	39.4	38.1
Management contracts	140.6	137.0	132.0
Total gross profit	185.3	176.4	170.1
General and administrative expenses	82.9	90.0	97.3
Depreciation and amortization	21.0	33.7	34.0
Operating income	81.4	52.7	38.8
Other expense (income)
Interest expense	9.2	10.5	12.7
Interest income	(0.6)	(0.5)	(0.2)
Gain on sale of a business	(0.1)	0.0	(0.5)
Equity in losses from investment in unconsolidated entity	0.7	0.9	1.7
Total other expenses (income)	9.2	10.9	13.7
Earnings before income taxes	72.2	41.8	25.1
Income tax expense	27.7	15.8	4.8
Net income	44.5	26.0	20.3
Less: Net income attributable to noncontrolling interest	3.3	2.9	2.9
Net income attributable to SP Plus Corporation	$ 41.2	$ 23.1	$ 17.4
Net income per common share
Basic (in dollars per share)	$ 1.86	$ 1.04	$ 0.78
Diluted (in dollars per share)	$ 1.83	$ 1.03	$ 0.77
Weighted average shares outstanding
Basic (in shares)	22,195,350	22,238,021	22,189,140
Diluted (in shares)	22,508,288	22,528,122	22,511,759