Business Unit Segment Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Parking Services Revenue
Lease contracts	$ 135.7	$ 146.5	$ 274.2	$ 282.3
Management contracts	86.7	88.3	177.9	182.4
Total parking services revenue	222.4	234.8	452.1	464.7
Reimbursed management contract revenue	180.2	170.8	348.1	345.1
Total revenue	402.6	405.6	800.2	809.8
Gross Profit
Lease contracts	11.7	12.0	19.6	19.1
Management contracts	35.3	34.4	65.8	68.6
Total gross profit	47.0	46.4	85.4	87.7
Gross Margin
General and administrative expenses	$ 22.1	$ 24.7	$ 46.7	$ 50.5
General and administrative expense percentage of gross profit	47.00%	53.00%	55.00%	58.00%
Depreciation and amortization	$ 9.8	$ 8.2	$ 19.0	$ 16.1
Operating income	15.1	13.5	19.7	21.1
Other expenses (income)
Interest expense	2.6	3.0	5.4	7.1
Interest income	(0.1)	0.0	(0.3)	(0.1)
Equity in losses from investment in unconsolidated entity	0.3	0.3	0.8	0.8
Total other expenses (income)	2.8	3.3	5.9	7.8
Earnings before income taxes	12.3	10.2	13.8	13.3
Income tax expense (benefit)	4.9	(0.3)	5.8	1.0
Net income	7.4	10.5	8.0	12.3
Less: Net income attributable to noncontrolling interest	0.9	0.7	1.5	1.2
Net income attributable to SP Plus Corporation	6.5	9.8	6.5	11.1
Operating segment \| Region One
Parking Services Revenue
Lease contracts	102.6	113.0	209.2	217.8
Management contracts	49.6	47.8	96.1	95.0
Total parking services revenue	152.2	160.8	305.3	312.8
Gross Profit
Lease contracts	10.0	11.9	17.1	17.6
Management contracts	21.8	21.1	41.4	41.9
Total gross profit	$ 31.8	$ 33.0	$ 58.5	$ 59.5
Gross Margin
Lease contracts (as a percent)	10.00%	11.00%	8.00%	8.00%
Management contracts (as a percent)	44.00%	44.00%	43.00%	44.00%
Operating segment \| Region Two
Parking Services Revenue
Lease contracts	$ 31.8	$ 32.4	$ 62.4	$ 62.1
Management contracts	24.3	26.1	48.4	51.6
Total parking services revenue	56.1	58.5	110.8	113.7
Gross Profit
Lease contracts	1.6	1.7	2.5	2.6
Management contracts	6.8	7.2	12.4	12.7
Total gross profit	$ 8.4	$ 8.9	$ 14.9	$ 15.3
Gross Margin
Lease contracts (as a percent)	5.00%	5.00%	4.00%	4.00%
Management contracts (as a percent)	28.00%	28.00%	26.00%	25.00%
Operating segment \| Region Three
Parking Services Revenue
Lease contracts	$ 1.2	$ 1.2	$ 2.6	$ 2.4
Management contracts	9.5	10.9	26.6	28.4
Total parking services revenue	10.7	12.1	29.2	30.8
Gross Profit
Lease contracts	(0.1)	0.0	0.3	0.2
Management contracts	2.6	2.8	6.4	6.4
Total gross profit	$ 2.5	$ 2.8	$ 6.7	$ 6.6
Gross Margin
Lease contracts (as a percent)	(8.00%)	0.00%	12.00%	8.00%
Management contracts (as a percent)	27.00%	26.00%	24.00%	23.00%
Corporate, Non-Segment
Parking Services Revenue
Lease contracts	$ 0.1	$ (0.1)	$ 0.0	$ 0.0
Management contracts	3.3	3.5	6.8	7.4
Total parking services revenue	3.4	3.4	6.8	7.4
Gross Profit
Lease contracts	0.2	(1.6)	(0.3)	(1.3)
Management contracts	4.1	3.3	5.6	7.6
Total gross profit	$ 4.3	$ 1.7	$ 5.3	$ 6.3
Gross Margin
Lease contracts (as a percent)	200.00%	(1600.00%)	0.00%	0.00%
Management contracts (as a percent)	124.00%	94.00%	82.00%	103.00%

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