Earnings (Loss) Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator [Abstract]
Net (loss) income attributable to Alliance HealthCare Services, Inc.	$ 4,011	$ (2,070)	$ 8,727	$ (17,452)
Denominator [Abstract]
Weighted-average shares-basic (shares)	10,710	10,639	10,683	10,632
Effect of dilutive securities:
Employee stock options (shares)	141	0	181	0
Weighted-average shares-diluted (shares)	10,851	10,639	10,864	10,632
Earnings Per Share, Basic and Diluted [Abstract]
Basic (dollars per share)	$ 0.37	$ (0.19)	$ 0.82	$ (1.64)
Diluted (dollars per share)	$ 0.37	$ (0.19)	$ 0.80	$ (1.64)
Antidilutive Securities Excluded From Computation Of Diluted Earnings Per Share [Abstract]
Weighted-average shares for which exercise price exceeds average market price of common stock (shares)	338	201	234	155
Average exercise price per share that exceeds average market price of common stock (dollars per share)	$ 34.74	$ 38.34	$ 37.70	$ 35.32