Business Unit Segment Information - Schedule of Revenues and Gross Profit by Regions (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Parking Services Revenue
Lease contracts	$ 150.9	$ 135.7	$ 281.7	$ 274.2
Management contracts	84.0	86.7	176.1	177.9
Total parking services revenue	234.9	222.4	457.8	452.1
Reimbursed management contract revenue	180.5	180.2	372.1	348.1
Total parking services revenue	415.4	402.6	829.9	800.2
Gross Profit
Lease contracts	20.7	11.7	25.7	19.6
Management contracts	36.8	35.3	72.3	65.8
Total gross profit	57.5	47.0	98.0	85.4
Gross Margin
General and administrative expenses	$ 22.5	$ 22.1	$ 43.7	$ 46.7
General and administrative expense percentage of gross profit	39.00%	47.00%	45.00%	55.00%
Depreciation and amortization	$ 4.8	$ 9.8	$ 11.4	$ 19.0
Operating income	30.2	15.1	42.9	19.7
Other expenses (income)
Interest expense	2.3	2.6	4.9	5.4
Interest income	(0.2)	(0.1)	(0.3)	(0.3)
Equity in losses from investment in unconsolidated entity	0.2	0.3	0.4	0.8
Total other expenses (income)	2.2	2.8	4.9	5.9
Earnings before income taxes	28.0	12.3	38.0	13.8
Income tax expense	10.7	4.9	14.0	5.8
Net income	17.3	7.4	24.0	8.0
Less: Net income attributable to noncontrolling interest	1.1	0.9	1.8	1.5
Net income attributable to SP Plus Corporation	16.2	6.5	22.2	6.5
Operating segment \| Region One
Parking Services Revenue
Lease contracts	117.4	103.9	217.1	211.8
Management contracts	59.3	60.0	127.6	124.5
Total parking services revenue	176.7	163.9	344.7	336.3
Gross Profit
Lease contracts	17.9	9.9	21.1	16.5
Management contracts	24.6	24.1	49.5	46.4
Total gross profit	$ 42.5	$ 34.0	$ 70.6	$ 62.9
Gross Margin
Lease contracts (as a percent)	15.00%	10.00%	10.00%	8.00%
Management contracts (as a percent)	41.00%	40.00%	39.00%	37.00%
Operating segment \| Region Two
Parking Services Revenue
Lease contracts	$ 33.5	$ 31.9	$ 64.6	$ 62.4
Management contracts	22.6	24.3	44.2	48.4
Total parking services revenue	56.1	56.2	108.8	110.8
Gross Profit
Lease contracts	2.0	1.8	3.3	2.5
Management contracts	7.2	7.4	13.3	11.7
Total gross profit	$ 9.2	$ 9.2	$ 16.6	$ 14.2
Gross Margin
Lease contracts (as a percent)	6.00%	6.00%	5.00%	4.00%
Management contracts (as a percent)	32.00%	30.00%	30.00%	24.00%
Corporate, Non-Segment
Parking Services Revenue
Lease contracts	$ 0.0	$ (0.1)	$ 0.0	$ 0.0
Management contracts	2.1	2.4	4.3	5.0
Total parking services revenue	2.1	2.3	4.3	5.0
Gross Profit
Lease contracts	0.8	0.0	1.3	0.6
Management contracts	5.0	3.8	9.5	7.7
Total gross profit	$ 5.8	$ 3.8	$ 10.8	$ 8.3
Gross Margin
Lease contracts (as a percent)	0.00%	0.00%	0.00%	0.00%
Management contracts (as a percent)	238.00%	158.00%	221.00%	154.00%

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