Financial Information for the Company and Its Subsidiaries - Summary of Condensed Consolidating Statement of Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 782,810				$ 760,617
Salaries, wages and benefits	440,316				429,579
Professional fees	63,300				57,007
Supplies	31,971				29,957
Rents and leases	20,824				20,307
Other operating expenses	98,529				93,865
Depreciation and amortization	41,680				40,580
Interest expense, net	42,785				48,130
Transaction-related expenses	3,549				4,321
Total expenses	742,954				723,746
(Loss) income before income taxes	39,856				36,871
(Benefit from) provision for income taxes	5,789				7,360
Net income	34,067				29,511
Net income attributable to noncontrolling interests	(604)				(40)
Net income attributable to Acadia Healthcare Company, Inc.	33,463	$ (11,254)	$ 42,566	$ 48,140	29,471
Other comprehensive income:
Foreign currency translation (loss) gain	(122,000)				44,481
Loss on derivative instruments	43,746				(8,690)
Other comprehensive (loss) income	(78,254)	$ 93,110	$ (48,377)	$ (33,031)	35,791
Comprehensive (loss) income attributable to Acadia Healthcare Company, Inc.	(44,791)				65,262
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Salaries, wages and benefits	4,979				6,101
Interest expense, net	14,460				19,578
Total expenses	19,439				25,679
(Loss) income before income taxes	(19,439)				(25,679)
Equity in earnings of subsidiaries	48,353				48,157
(Benefit from) provision for income taxes	(5,153)				(7,033)
Net income	34,067				29,511
Net income attributable to Acadia Healthcare Company, Inc.	34,067				29,511
Other comprehensive income:
Loss on derivative instruments	43,746				(8,690)
Other comprehensive (loss) income	43,746				(8,690)
Comprehensive (loss) income attributable to Acadia Healthcare Company, Inc.	77,813				20,821
Combined Subsidiary Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Revenue	474,612				459,818
Salaries, wages and benefits	261,603				254,942
Professional fees	28,558				25,368
Supplies	20,859				19,384
Rents and leases	8,883				8,403
Other operating expenses	63,819				59,390
Depreciation and amortization	21,046				19,605
Interest expense, net	24,159				23,018
Transaction-related expenses	1,525				3,218
Total expenses	430,452				413,328
(Loss) income before income taxes	44,160				46,490
(Benefit from) provision for income taxes	11,712				17,065
Net income	32,448				29,425
Net income attributable to Acadia Healthcare Company, Inc.	32,448				29,425
Other comprehensive income:
Comprehensive (loss) income attributable to Acadia Healthcare Company, Inc.	32,448				29,425
Combined Non-Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Revenue	308,198				300,799
Salaries, wages and benefits	173,734				168,536
Professional fees	34,742				31,639
Supplies	11,112				10,573
Rents and leases	11,941				11,904
Other operating expenses	34,710				34,475
Depreciation and amortization	20,634				20,975
Interest expense, net	4,166				5,534
Transaction-related expenses	2,024				1,103
Total expenses	293,063				284,739
(Loss) income before income taxes	15,135				16,060
(Benefit from) provision for income taxes	(770)				(2,672)
Net income	15,905				18,732
Net income attributable to noncontrolling interests	(604)				(40)
Net income attributable to Acadia Healthcare Company, Inc.	15,301				18,692
Other comprehensive income:
Foreign currency translation (loss) gain	(122,000)				44,481
Other comprehensive (loss) income	(122,000)				44,481
Comprehensive (loss) income attributable to Acadia Healthcare Company, Inc.	(106,699)				63,173
Consolidating Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Equity in earnings of subsidiaries	(48,353)				(48,157)
Net income	(48,353)				(48,157)
Net income attributable to Acadia Healthcare Company, Inc.	(48,353)				(48,157)
Other comprehensive income:
Comprehensive (loss) income attributable to Acadia Healthcare Company, Inc.	$ (48,353)				$ (48,157)