Business Unit Segment Information - Schedule of Revenues and Gross Profit by Regions (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Parking Services Revenue
Lease type contracts	$ 99.5	$ 130.8
Management type contracts	94.4	92.1
Total parking services revenue	193.9	222.9
Reimbursed management type contract revenue	172.9	179.0
Total parking services revenue	366.8	401.9
Gross Profit
Lease type contracts	4.9	5.0
Management type contracts	34.5	35.5
Total gross profit	39.4	40.5
Gross Margin
General and administrative expenses	$ 22.3	$ 21.2
General and administrative expense percentage of gross profit	57.00%	52.00%
Depreciation and amortization	$ 4.0	$ 6.6
Operating income	13.1	12.7
Other expenses (income)
Interest expense	2.1	2.6
Interest expense	(0.1)	(0.1)
Equity (earnings) losses from investment in unconsolidated entity	(10.1)	0.2
Total other (income) expenses	(8.1)	2.7
Earnings before income taxes	21.2	10.0
Income tax expense	5.3	3.3
Net income	15.9	6.7
Less: Net income attributable to noncontrolling interest	0.6	0.7
Net income attributable to SP Plus Corporation	15.3	6.0
Operating segment \| Region One
Parking Services Revenue
Lease type contracts	93.1	99.8
Management type contracts	69.5	68.1
Total parking services revenue	162.6	167.9
Gross Profit
Lease type contracts	2.3	3.3
Management type contracts	23.7	24.6
Total gross profit	$ 26.0	$ 27.9
Gross Margin
Lease contracts (as a percent)	2.00%	3.00%
Management contracts (as a percent)	34.00%	36.00%
Operating segment \| Region Two
Parking Services Revenue
Lease type contracts	$ 6.4	$ 31.0
Management type contracts	22.3	21.8
Total parking services revenue	28.7	52.8
Gross Profit
Lease type contracts	1.4	1.2
Management type contracts	5.9	6.3
Total gross profit	$ 7.3	$ 7.5
Gross Margin
Lease contracts (as a percent)	22.00%	4.00%
Management contracts (as a percent)	26.00%	29.00%
Segment Reconciling Items
Parking Services Revenue
Lease type contracts	$ 0.0	$ 0.0
Management type contracts	2.6	2.2
Total parking services revenue	2.6	2.2
Gross Profit
Lease type contracts	1.2	0.5
Management type contracts	4.9	4.6
Total gross profit	$ 6.1	$ 5.1
Gross Margin
Lease contracts (as a percent)	0.00%	0.00%
Management contracts (as a percent)	188.00%	209.00%

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