Business Unit Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Parking Services Revenue
Lease contracts	$ 136.1	$ 146.6	$ 410.3	$ 428.9
Management contracts	84.1	85.8	262.0	268.2
Total parking services revenue	220.2	232.4	672.3	697.1
Reimbursed management contract revenue	188.9	168.3	537.0	513.4
Total revenue	409.1	400.7	1,209.3	1,210.5
Gross Profit
Lease contracts	10.3	10.6	29.9	29.8
Management contracts	33.6	32.2	99.4	100.7
Total gross profit	43.9	42.8	129.3	130.5
Gross Margin
General and administrative expenses	$ 20.3	$ 23.7	$ 67.0	$ 74.2
General and administrative expense percentage of gross profit	46.20%	55.40%	51.80%	56.90%
Depreciation and amortization	$ 7.8	$ 8.3	$ 26.8	$ 24.4
Operating income	15.8	10.8	35.5	31.9
Other expenses (income)
Interest expense	2.7	2.9	8.1	10.0
Interest income	(0.1)	0.0	(0.4)	(0.1)
Gain on a sale of business	0.0	(0.5)	0.0	(0.5)
Equity in losses from investment in unconsolidated entity	0.4	0.4	1.2	1.2
Total other expenses	3.0	2.8	8.9	10.6
Earnings before income taxes	12.8	8.0	26.6	21.3
Income tax expense	5.1	3.5	10.9	4.5
Net income	7.7	4.5	15.7	16.8
Less: Net income attributable to noncontrolling interest	0.7	0.8	2.2	2.0
Net income attributable to SP Plus Corporation	7.0	3.7	13.5	14.8
Operating segment | Region One
Parking Services Revenue
Lease contracts	103.1	113.8	312.3	330.9
Management contracts	51.2	47.7	147.3	142.6
Total parking services revenue	154.3	161.5	459.6	473.5
Gross Profit
Lease contracts	8.1	10.9	25.3	28.4
Management contracts	21.3	21.5	62.8	63.3
Total gross profit	$ 29.4	$ 32.4	$ 88.1	$ 91.7
Gross Margin
Lease contracts (as a percent)	7.90%	9.60%	8.10%	8.60%
Management contracts (as a percent)	41.60%	45.10%	42.60%	44.40%
Operating segment | Region Two
Parking Services Revenue
Lease contracts	$ 31.3	$ 31.8	$ 93.7	$ 94.4
Management contracts	20.7	26.6	69.2	78.2
Total parking services revenue	52.0	58.4	162.9	172.6
Gross Profit
Lease contracts	1.5	1.7	4.0	4.4
Management contracts	6.1	5.7	18.7	18.4
Total gross profit	$ 7.6	$ 7.4	$ 22.7	$ 22.8
Gross Margin
Lease contracts (as a percent)	4.80%	5.30%	4.30%	4.70%
Management contracts (as a percent)	29.50%	21.40%	27.00%	23.50%
Operating segment | Region Three
Parking Services Revenue
Lease contracts	$ 1.7	$ 1.1	$ 4.3	$ 3.5
Management contracts	9.0	8.2	35.6	36.6
Total parking services revenue	10.7	9.3	39.9	40.1
Gross Profit
Lease contracts	0.3	0.1	0.5	0.3
Management contracts	3.1	2.8	9.4	9.3
Total gross profit	$ 3.4	$ 2.9	$ 9.9	$ 9.6
Gross Margin
Lease contracts (as a percent)	17.60%	9.10%	11.60%	8.60%
Management contracts (as a percent)	34.40%	34.10%	26.40%	25.40%
Corporate, Non-Segment
Parking Services Revenue
Lease contracts	$ 0.0	$ (0.1)	$ 0.0	$ 0.1
Management contracts	3.2	3.3	9.9	10.8
Total parking services revenue	3.2	3.2	9.9	10.9
Gross Profit
Lease contracts	0.4	(2.1)	0.1	(3.3)
Management contracts	3.1	2.2	8.5	9.7
Total gross profit	$ 3.5	$ 0.1	$ 8.6	$ 6.4
Gross Margin
Lease contracts (as a percent)	0.00%	(2100.00%)	0.00%	(3300.00%)
Management contracts (as a percent)	96.90%	66.70%	85.90%	89.80%