Segment Information (Reconciliation of Net Loss to Segment Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Reconciliation of Net loss to total segment income
Net (loss) income attributable to Alliance HealthCare Services, Inc.	$ 4,011	$ (2,070)	$ 8,727	$ (17,452)
Income tax (benefit) expense	2,948	(2,392)	6,256	(9,725)
Interest expense and other, net	6,208	8,156	18,570	31,481
Amortization expense	1,961	2,151	5,870	8,856
Depreciation expense	12,743	16,965	42,812	49,803
Share-based payment (included in selling, general and administrative expenses)	407	301	1,117	1,036
Severance and related costs	455	660	2,315	1,306
Noncontrolling interest in subsidiaries	3,843	3,402	10,928	9,741
Restructuring charges (Note 2)	(264)	1,809	2,191	5,172
Transaction costs	573	7	1,512	87
Impairment charges	4	4,529	240	9,396	4,867
Loss on extinguishment of debt	0	5,132	0	22,201	17,069
Legal settlements	2,000	514	3,621	1,464
Other non-cash charges (included in other income and expense, net)	64	52	415	242
Total segment income	$ 34,953	$ 38,556	$ 104,574	$ 112,302