Net Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013 item	Dec. 31, 2012 item
Net Income Per Common Share
Net income attributable to SP Plus Corporation	$ 9,186	$ 4,302	$ 5,307	$ 4,303	$ 5,161	$ 3,744	$ 3,444	$ (260)	$ 23,098	$ 12,089	$ 1,340
Basic (in shares)	22,071,706	21,997,394	21,991,965	21,977,836	21,938,377	21,911,574	21,889,777	21,870,771	22,009,800	21,902,870	17,179,606
Dilutive impact of share-based awards									397,543	346,714	310,598
Diluted weighted average common shares outstanding	22,451,557	22,426,787	22,398,886	22,351,845	22,319,723	22,285,723	22,221,102	21,870,771	22,407,343	22,249,584	17,490,204
Net income (loss) per share:
Basic (in dollars per share)	$ 0.42	$ 0.20	$ 0.24	$ 0.20	$ 0.24	$ 0.17	$ 0.16	$ (0.01)	$ 1.05	$ 0.55	$ 0.08
Diluted (in dollars per share)	$ 0.41	$ 0.19	$ 0.24	$ 0.19	$ 0.23	$ 0.17	$ 0.15	$ (0.01)	$ 1.03	$ 0.54	$ 0.08
Performance-based incentive programs										0	0
Potential shares of common stock attributable to stock options excluded from net income per common share calculation									0	0	0