Net Income (Loss) Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014 item
Net Income (Loss) Per Common Share
Net income attributable to SP Plus Corporation	$ 1,342	$ 4,303
Weighted average common basic shares outstanding	22,127,725	21,977,836
Effect of dilutive stock options and restricted stock units	400,884	374,009
Weighted average common diluted shares outstanding	22,528,609	22,351,845
Net income (loss) per share:
Basic (in dollars per share)	$ 0.06us-gaap_EarningsPerShareBasic	$ 0.20us-gaap_EarningsPerShareBasic
Diluted (in dollars per share)	$ 0.06us-gaap_EarningsPerShareDiluted	$ 0.19us-gaap_EarningsPerShareDiluted
Performance-based incentive programs		0stan_PerformanceBasedIncentivePrograms
Potential shares of common stock attributable to stock options excluded from net income per common share calculation	0

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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