Segment Information - Reconciliation of Net Income (Loss) to Total Segment Income (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Jun. 03, 2013	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of net income to total segment income
Net income (loss) attributable to Alliance HealthCare Services, Inc.		$ (252)	$ 7,204	$ (1,961)	$ 1,751	$ 1,892	$ 4,011	$ 2,784	$ 1,931	$ 6,742	$ 10,618	$ (21,483)
Income tax expense (benefit)										6,536	7,327	(12,398)
Interest expense and other, net										26,241	24,693	39,170
Amortization expense										9,325	7,880	10,973
Depreciation expense										48,595	54,971	66,319
Share-based payment (included in selling, general and administrative expenses)										1,012	830	925
Severance and related costs										1,347	2,517	1,658
Noncontrolling interest in subsidiaries										20,373	14,883	13,041
Restructuring charges										1,327	2,602	7,182
Shareholder transaction costs										1,853
Impairment charges										6,817	308	13,031
Loss on extinguishment of debt	$ 17,069											26,018
Non-cash gain on step acquisition (included in other income and expense, net)										10,672
Segment Reconciling Items
Reconciliation of net income to total segment income
Income tax expense (benefit)										6,536	7,327	(12,398)
Interest expense and other, net										26,241	24,693	39,170
Amortization expense										9,100	7,880	10,973
Depreciation expense										48,595	54,971	66,319
Share-based payment (included in selling, general and administrative expenses)										1,701	1,515	1,487
Severance and related costs										1,320	2,517	0
Noncontrolling interest in subsidiaries										20,373	14,883	13,041
Restructuring charges										1,327	2,602	7,182
Transaction costs										3,296	2,344	465
Shareholder transaction costs										1,853	0	0
Impairment charges										6,817	308	13,031
Loss on extinguishment of debt										0	0	26,018
Legal matters expense										6,915	5,587	3,067
Non-cash gain on step acquisition (included in other income and expense, net)										(10,672)	0	0
Other non-cash charges (included in other income and expense, net)										1,116	510	549
Operating Segments
Reconciliation of net income to total segment income
Net income (loss) attributable to Alliance HealthCare Services, Inc.										$ 131,260	$ 135,755	$ 147,421