Net Income per Common Share (Details) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Mar. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) incentive_program $ / shares shares
Earnings Per Share [Abstract]
Net income attributable to SP Plus Corporation | $	$ 2.6	$ 3.6	$ 9.8	$ 1.4	$ 9.3	$ 4.2	$ 5.4	$ 4.2	$ 17.4	$ 23.1	$ 12.1
Basic (in shares)	22,276,763	22,205,707	22,145,190	22,127,725	22,071,706	21,997,394	21,991,965	21,977,836	22,189,140	22,009,800	21,902,870
Dilutive impact of share-based awards (in shares)									300,000	400,000	300,000
Diluted (in shares)	22,486,888	22,548,166	22,521,832	22,528,608	22,451,557	22,426,787	22,398,886	22,351,845	22,511,759	22,407,343	22,249,584
Net income per common share
Basic (in dollars per share) | $ / shares	$ 0.11	$ 0.17	$ 0.44	$ 0.06	$ 0.42	$ 0.20	$ 0.24	$ 0.20	$ 0.78	$ 1.05	$ 0.55
Diluted (in dollars per share) | $ / shares	$ 0.11	$ 0.16	$ 0.43	$ 0.06	$ 0.41	$ 0.19	$ 0.24	$ 0.19	$ 0.77	$ 1.03	$ 0.54
Performance-based incentive programs | incentive_program											0
Antidilutive securities excluded from computation of earnings per share, amount									0	0	0