LifeStance Health (LFST) 10-Q 10 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Entity Registrant Name	LifeStance Health Group, Inc.
Entity Central Index Key	0001845257
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Shell Company	false
Document Quarterly Report	true
Document Transition Report	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	LFST
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NASDAQ
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		374,148,648
Entity File Number	001-40478
Entity Tax Identification Number	86-1832801
Entity Address, Address Line Two	Suite 6000
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	4800 N. Scottsdale Road
Entity Address, City or Town	Scottsdale
Entity Address, State or Province	AZ
Entity Address, Postal Zip Code	85251
City Area Code	602
Local Phone Number	767-2100

CONSOLIDATED BALANCE SHEETS (un

CONSOLIDATED BALANCE SHEETS (unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS
Cash and cash equivalents	$ 212,123	$ 18,829
Patient accounts receivable	70,059	43,706
Prepaid expenses and other current assets	46,144	13,745
Total current assets	328,326	76,280
NONCURRENT ASSETS
Property and equipment, net	115,049	59,349
Intangible assets, net	307,982	332,796
Goodwill	1,160,011	1,098,659
Deposits	3,388	2,647
Total noncurrent assets	1,586,430	1,493,451
Total assets	1,914,756	1,569,731
CURRENT LIABILITIES
Accounts payable	3,074	7,688
Accrued payroll expenses	57,603	38,024
Other accrued expenses	28,331	14,685
Current portion of contingent consideration	14,012	10,563
Other current liabilities	2,185	4,961
Total current liabilities	105,205	75,921
NONCURRENT LIABILITIES
Long-term debt, net	157,447	362,534
Other noncurrent liabilities	22,892	11,363
Contingent consideration, net of current portion	3,117	5,851
Deferred tax liability, net	81,226	81,226
Total noncurrent liabilities	264,682	460,974
Total liabilities	369,887	536,895
COMMITMENT AND CONTINGENCIES (see Note 16)
STOCKHOLDERS’/MEMBERS’ EQUITY
Preferred stock - par value $0.01 per share; 25,000 and 0 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 0 shares issued and outstanding as of September 30, 2021 and December 31, 2020
Common stock - par value $0.01 per share; 800,000 and 0 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 374,149 and 0 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	3,742	0
Additional paid-in capital	1,790,169	1,452
Accumulated deficit	(249,042)	(13,125)
Total stockholders'/members’ equity	1,544,869	997,836
Total liabilities, redeemable units and stockholders’/members’ equity	1,914,756	1,569,731
Redeemable Class A Unit
REDEEMABLE UNITS
Redeemable Class A units - 0 and 35,000 units authorized, issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	0	35,000
Common Unit Class A-1
STOCKHOLDERS’/MEMBERS’ EQUITY
Common Unit, Issuance Value	0	959,563
Common Unit Class A-2
STOCKHOLDERS’/MEMBERS’ EQUITY
Common Unit, Issuance Value	0	49,946
Common Unit Class B
STOCKHOLDERS’/MEMBERS’ EQUITY
Common Unit, Issuance Value	$ 0	$ 0

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - $ / shares shares in Thousands	Sep. 30, 2021	Dec. 31, 2020
Common Unit, Outstanding	374,149	1,044,509
Preferred Stock, par value	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	25,000	0
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, Shares Authorized	800,000	0
Common Stock, Shares, Issued	374,149	0
Common Stock, Shares, Outstanding	374,149	0
Redeemable Class A Unit
Temporary Equity, Shares Authorized	0	35,000
Temporary Equity, Shares Issued	0	35,000
Temporary Equity, Shares Outstanding	0	35,000
Common Unit Class A-1
Common Unit, Authorized	0	959,563
Common Unit, Issued	0	959,563
Common Unit, Outstanding	0	959,563
Common Unit Class A-2
Common Unit, Authorized	0	49,946
Common Unit, Issued	0	49,946
Common Unit, Outstanding	0	49,946
Common Unit Class B
Common Unit, Authorized	0	179,000
Common Unit, Issued	0	0
Common Unit, Outstanding	0	0

UNAUDITED CONSOLIDATED STATEMEN

UNAUDITED CONSOLIDATED STATEMENTS OF INCOME/(LOSS) AND COMPREHENSIVE INCOME/(LOSS) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
TOTAL REVENUES	$ 173,835	$ 101,982	$ 111,661	$ 147,435	$ 477,516
OPERATING EXPENSES
Center costs, excluding depreciation and amortization shown separately below	121,783	68,847	78,777	100,122	330,258
General and administrative expenses	162,943	19,534	20,854	28,176	281,073
Depreciation and amortization	13,777	10,910	3,335	16,342	38,779
Total operating expenses	298,503	99,291	102,966	144,640	650,110
(LOSS) INCOME FROM OPERATIONS	(124,668)	2,691	8,695	2,795	(172,594)
OTHER INCOME (EXPENSE)
(Loss) gain on remeasurement of contingent consideration	(906)	89	322	38	(1,463)
Transaction costs	(126)	(683)	(33,247)	(864)	(3,656)
Interest expense	(3,503)	(6,421)	(3,020)	(11,983)	(35,309)
Other expense	0	(44)	(14)	(66)	(1,445)
Total other expense	(4,535)	(7,059)	(35,959)	(12,875)	(41,873)
LOSS BEFORE INCOME TAXES	(129,203)	(4,368)	(27,264)	(10,080)	(214,467)
INCOME TAX BENEFIT	8,751	1,074	2,319	2,444	15,300
NET LOSS AND COMPREHENSIVE LOSS	(120,452)	(3,294)	(24,945)	(7,636)	(199,167)
Accretion of Redeemable Class A units					(36,750)
Cumulative dividend on Series A redeemable convertible preferred units (Note 12)	0	0	(662)	0	0
NET LOSS AVAILABLE TO COMMON STOCKHOLDERS/MEMBERS	$ (120,452)	$ (3,294)	(298,189)	$ (7,636)	$ (235,917)
NET LOSS PER SHARE, BASIC AND DILUTED	$ (0.35)	$ (0.01)		$ (0.03)	$ (0.73)
Weighted-average shares used to compute basic and diluted net loss per share	343,394	302,657		300,799	321,283
Series A Preferred Stock
OTHER INCOME (EXPENSE)
Accretion of Redeemable Class A units	$ 0	$ 0	0	$ 0	$ (36,750)
Series A1 Preferred Stock
OTHER INCOME (EXPENSE)
Accretion of Redeemable Class A units	$ 0	$ 0	$ (272,582)	$ 0	$ 0

UNAUDITED CONSOLIDATED STATEM_2

UNAUDITED CONSOLIDATED STATEMENT OF CHANGES IN REDEEMABLE UNITS AND STOCKHOLDERS' / MEMBERS' EQUITY - USD ($) $ in Thousands	Total	T P G Acquisition	I P O [Member]	Class A Redeemable Units [Member]	Class A Redeemable Units [Member]T P G Acquisition	Class A-1 Common Units [Member]	Class A-1 Common Units [Member]T P G Acquisition	Class A-2 Common Units [Member]	Class A-2 Common Units [Member]T P G Acquisition	Class B Common Units [Member]	Series A Redeemable Convertible Preferred Units	Series A1 Redeemable Convertible Preferred Units	Class A Common Units	Class C Common Units	Common Stock [Member]	Common Stock [Member]I P O [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]I P O [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Series A Redeemable Convertible Preferred Units	Accumulated Deficit [Member]Series A1 Redeemable Convertible Preferred Units
Balance at Dec. 31, 2019	$ (166,355)												$ 3	$ 0			$ 0		$ (166,358)
Temporary Equity, Shares Outstanding at Dec. 31, 2019											16,459,000	109,838,000
Temporary Equity, Carrying Amount, Attributable to Parent at Dec. 31, 2019											$ 20,261	$ 282,652
Shares, Outstanding at Dec. 31, 2019													25,252,000	4,980,000
Net loss	(24,945)																		(24,945)
Accretion of Redeemable Class A units												$ (272,582)									$ (272,582)
Issuance of common units for acquisitions of businesses	0
Issuance of common units for convertible promissory note conversion	0
Repurchases of Series A redeemable convertible preferred units	1,000										$ 500									$ 500
Repurchases of Series A redeemable convertible preferred units, shares											(333,000)
Balance at May. 14, 2020	(464,382)												$ 3	$ 0			0		(464,385)
Temporary Equity, Shares Outstanding at May. 14, 2020											16,126,000	109,838,000
Temporary Equity, Carrying Amount, Attributable to Parent at May. 14, 2020											$ 19,761	$ 555,234
Shares, Outstanding at May. 14, 2020													25,252,000	4,980,000
Balance at Apr. 13, 2020	0					$ 0		$ 0		$ 0							0		0
Temporary Equity, Shares Outstanding at Apr. 13, 2020				0
Temporary Equity, Carrying Amount, Attributable to Parent at Apr. 13, 2020				$ 0
Shares, Outstanding at Apr. 13, 2020						0		0		0
Net loss	(7,636)																		(7,636)
Issuance of common units to new investors - Value	21,000	$ 633,585				$ 15,000	$ 633,585	$ 6,000
Issuance of common units to new investors - Shares						15,000,000	633,585,000	6,000,000
Issuance of common units for acquisitions of businesses	4,500	$ 346,823			$ 35,000		$ 310,978	$ 4,500	$ 35,845
Issuance of common units for acquisitions of businesses, shares					35,000,000		310,978,000	4,500,000	35,845,000
Stock and unit-based compensation	865																865
Issuance of common units for convertible promissory note conversion	511							$ 511
Issuance of common units for convertible promissory note conversion, shares								511,000
Balance at Sep. 30, 2020	999,648					$ 959,563		$ 46,856		$ 0							865		(7,636)
Temporary Equity, Shares Outstanding at Sep. 30, 2020				35,000,000
Temporary Equity, Carrying Amount, Attributable to Parent at Sep. 30, 2020				$ 35,000
Shares, Outstanding at Sep. 30, 2020						959,563,000		46,856,000		0
Balance at Apr. 13, 2020	$ 0					$ 0		$ 0		$ 0							0		0
Temporary Equity, Shares Outstanding at Apr. 13, 2020				0
Temporary Equity, Carrying Amount, Attributable to Parent at Apr. 13, 2020				$ 0
Shares, Outstanding at Apr. 13, 2020						0		0		0
Issuance of common units to new investors - Shares	1,044,509,000
Balance at Dec. 31, 2020	$ 997,836					$ 959,563		$ 49,946		$ 0					$ 0		1,452		(13,125)
Temporary Equity, Shares Outstanding at Dec. 31, 2020				35,000,000
Temporary Equity, Carrying Amount, Attributable to Parent at Dec. 31, 2020				$ 35,000
Shares, Outstanding at Dec. 31, 2020						959,563,000		49,946,000		0					0
Balance at Jun. 30, 2020	981,369					$ 944,563		$ 40,856		$ 0							292		(4,342)
Temporary Equity, Shares Outstanding at Jun. 30, 2020				35,000,000
Temporary Equity, Carrying Amount, Attributable to Parent at Jun. 30, 2020				$ 35,000
Shares, Outstanding at Jun. 30, 2020						944,563,000		40,856,000		0
Net loss	(3,294)																		(3,294)
Issuance of common units to new investors - Value	21,000					$ 15,000		$ 6,000
Issuance of common units to new investors - Shares						15,000,000		6,000,000
Stock and unit-based compensation	573																573
Balance at Sep. 30, 2020	999,648					$ 959,563		$ 46,856		$ 0							865		(7,636)
Temporary Equity, Shares Outstanding at Sep. 30, 2020				35,000,000
Temporary Equity, Carrying Amount, Attributable to Parent at Sep. 30, 2020				$ 35,000
Shares, Outstanding at Sep. 30, 2020						959,563,000		46,856,000		0
Balance at Dec. 31, 2020	997,836					$ 959,563		$ 49,946		$ 0					$ 0		1,452		(13,125)
Temporary Equity, Shares Outstanding at Dec. 31, 2020				35,000,000
Temporary Equity, Carrying Amount, Attributable to Parent at Dec. 31, 2020				$ 35,000
Shares, Outstanding at Dec. 31, 2020						959,563,000		49,946,000		0					0
Net loss	(199,167)																		(199,167)
Issuance of common units to new investors - Value	$ 1,000		$ 548,905					$ 1,000								$ 328		$ 548,577
Issuance of common units to new investors - Shares	1,687,000							962,000								32,800,000
Accretion of Redeemable Class A units	$ (36,750)			(36,750)															(36,750)
Issuance of common units for acquisitions of businesses	$ 1,486							$ 1,486
Issuance of common units for acquisitions of businesses, shares								725,000
Vested Class B Profits Interest	17,920,000									17,920,000
Conversion of Redeemable Class A Units into common stock upon closing of initial public offering, Value	$ 71,750			$ (71,750)											$ 102		71,648
Conversion of Redeemable Class A Units into common stock upon closing of initial public offering, Shares				(35,000,000)											10,234,000
Conversion of common units into common stock upon closing of initial public offering, Value						$ (959,563)		$ (52,432)							$ 2,957		1,009,038
Conversion of common units into common stock upon closing of initial public offering, Shares						959,563,000		51,633,000							295,663,000
Conversion of vested Class Profits Interests to common stock upon closing of initial public offering										(17,920,000)					4,186,000
Conversion of vested Class Profits Interests to common stock upon closing of initial public offering Value															$ 42		(42)
Conversion of Unvested Class Profits Interests to Common Stock Upon Closing of Initial Public Offering Value															$ 308		(308)
Conversion of Unvested Class Profits Interests to Common Stock Upon Closing of Initial Public Offering Share															30,766,000
Endowment of shares to the LifeStance Health Foundation, Shares															500,000
Endowment of shares to the LifeStance Health Foundation, Value	9,000														$ 5		8,995
Stock and unit-based compensation	150,809																150,809
Issuance of common units for convertible promissory note conversion	0
Repurchases of Series A redeemable convertible preferred units	0
Balance at Sep. 30, 2021	1,544,869					$ 0		$ 0		$ 0					$ 3,742		1,790,169		(249,042)
Temporary Equity, Shares Outstanding at Sep. 30, 2021				0
Temporary Equity, Carrying Amount, Attributable to Parent at Sep. 30, 2021				$ 0
Shares, Outstanding at Sep. 30, 2021						0		0		0					374,149,000
Balance at Jun. 30, 2021	1,544,632														$ 3,742		1,669,480		(128,590)
Shares, Outstanding at Jun. 30, 2021															374,149,000
Net loss	(120,452)																		(120,452)
Stock and unit-based compensation	120,689																120,689
Balance at Sep. 30, 2021	$ 1,544,869					$ 0		$ 0		$ 0					$ 3,742		$ 1,790,169		$ (249,042)
Temporary Equity, Shares Outstanding at Sep. 30, 2021				0
Temporary Equity, Carrying Amount, Attributable to Parent at Sep. 30, 2021				$ 0
Shares, Outstanding at Sep. 30, 2021						0		0		0					374,149,000

UNAUDITED CONSOLIDATED STATEM_3

UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	4 Months Ended	6 Months Ended	9 Months Ended
	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (24,945)	$ (7,636)	$ (199,167)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	3,335	16,342	38,779
Stock and unit-based compensation	0	865	150,809
Deferred income taxes	(2,345)	2,866	0
Loss on debt extinguishment	0	3,066	5,620
Amortization of debt issue costs	215	358	1,498
Loss (gain) on remeasurement of contingent consideration	(322)	(38)	1,463
Endowment of shares to LifeStance Health Foundation	0	0	9,000
Change in operating assets and liabilities, net of businesses acquired:
Patient accounts receivable	(5,122)	(4,939)	(20,711)
Prepaid expenses and other current assets	(4,526)	(6,468)	(32,888)
Accounts payable	(1,638)	1,056	(4,613)
Accrued payroll expenses	8,753	1,529	15,910
Other accrued expenses	40,031	(33,130)	13,085
Net cash (used in) provided by operating activities	13,436	(26,129)	(21,215)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(12,804)	(14,653)	(55,815)
Acquisition of Predecessor, net of cash acquired	0	(646,694)	0
Acquisitions of businesses, net of cash acquired	(12,274)	(30,100)	(58,699)
Net cash used in investing activities	(25,078)	(691,447)	(114,514)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from initial public offering	0	0	548,905
Contributions from Members related to acquisition of Predecessor	0	633,585	0
Issuance of common units to new investors	0	21,000	1,000
Repurchase of Series A redeemable convertible preferred units	(1,000)	0	0
Proceeds from long-term debt	74,350	235,900	98,800
Payments of debt issue costs	(650)	(6,411)	(2,360)
Payments of long-term debt	(18,222)	(139,130)	(311,060)
Payments of contingent consideration	(19,093)	(2,300)	(6,262)
Net cash provided by financing activities	35,385	742,644	329,023
NET INCREASE IN CASH AND CASH EQUIVALENTS	23,743	25,068	193,294
Cash and Cash Equivalents - Beginning of period	3,481	0	18,829
CASH AND CASH EQUIVALENTS – END OF PERIOD	27,224	25,068	212,123
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid for interest and prepayment premium	2,857	8,555	28,217
Cash paid for taxes	25	144	908
SUPPLEMENTAL DISCLOSURES OF NON CASH INVESTING AND FINANCING ACTIVITIES
Equipment financed through capital leases	415	7	14
Contingent consideration incurred in acquisitions of businesses	3,788	4,226	5,514
Acquisition of property and equipment included in liabilities	2,718	2,562	8,936
Issuance of common units for convertible promissory note conversion	0	511	0
Issuance of common units for acquisitions of businesses	$ 0	$ 4,500	$ 1,486

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	NOTE 1 NATURE OF THE BUSINESS Description of Business LifeStance Health Group, Inc. (“LifeStance Health Group”) was formed as a Delaware corporation on January 28, 2021 for the purpose of completing an initial public offering (“IPO”) and related transactions in order to carry on the business of LifeStance TopCo, L.P. (“LifeStance TopCo”) and subsidiaries. LifeStance Health Group is the sole equity holder of LifeStance TopCo and operates and controls all of the business and affairs. As a result, LifeStance Health Group consolidates the financial results of LifeStance TopCo, its wholly-owned subsidiaries and variable interest entities. LifeStance Health Group and LifeStance TopCo are collectively referred to herein as the “Company”, "LifeStance" or "LifeStance Health". The Company operates as a provider of outpatient mental health services, spanning psychiatric evaluations and treatment, psychological and neuropsychological testing, and individual, family and group therapy. Initial Public Offering On June 14, 2021, the Company completed its IPO in which it issued and sold 32,800 shares of common stock and affiliates of TPG Global LLC ("TPG"), affiliates of Silversmith Capital Partners ("Silversmith"), and affiliates of Summit Partners ("Summit") (collectively, the "Selling Shareholders") sold 7,200 shares of common stock at an offering price of $ 18.00 per share. The Selling Shareholders granted the underwriters an option to purchase an additional 6,000 shares of common stock. The underwriters exercised in full their option to purchase additional shares, and the sale of the option shares was completed on June 25, 2021. The Company received net proceeds of $ 548,905 , after deducting underwriting discounts and commissions of $ 32,472 and deferred offering costs of $ 9,023 . The Company did not receive any proceeds from the sale of shares by the Selling Stockholders, including the option shares. Deferred, direct offering costs were capitalized and consisted of fees and expenses incurred in connection with the sale of the Company’s common stock in the IPO, including legal, accounting, printing and other offering related costs. Upon completion of the IPO, these deferred offering costs were reclassified from current assets to stockholders’ equity and recorded against the net proceeds from the offering. Prior to the IPO, each of the holders of partnership interests in LifeStance TopCo contributed its partnership interests to LifeStance Health Group in exchange for shares of common stock (including shares of common stock issued as restricted stock subject to vesting) of LifeStance Health Group (the "Organizational Transactions"). Following the contribution of partnership interests, LifeStance TopCo became wholly-owned by LifeStance Health Group. The number of shares of common stock that each such holder of partnership interests in LifeStance TopCo received was determined based on the value that such holder would have received under the distribution provisions of the limited partnership agreement of LifeStance TopCo, with shares of common stock valued by reference to the IPO price. All 1,046,196 of LifeStance TopCo’s outstanding redeemable and common Class A units and 152,620 Class B units (the "Class B Common Units", "Profits Interests Units" or "Profits Interests") were contributed in exchange for 310,083 shares of common stock of LifeStance Health Group plus 30,766 shares of common stock issued as restricted stock subject to vesting. As a result of this contribution and exchange, the Company reclassified $ 71,648 of redeemable units and $ 1,008,688 of common units to additional paid-in capital and $ 3,408 to common stock on the Company’s consolidated balance sheets. In connection with the IPO, the Company established the LifeStance Health Foundation, a non-profit organization that focuses on youth mental health, and the mental health of underrepresented minority communities, the underemployed and the uninsured. While the LifeStance Health Foundation was founded by LifeStance and will be operated by a board of directors that the Company expects to include from time to time certain of its officers and employees, including its Chief Executive Officer, the LifeStance Health Foundation was established as an independent legal entity and will not be owned or controlled by LifeStance or its stockholders. Concurrently with the closing of the IPO, the Company endowed the LifeStance Health Foundation through a combination of $ 1,000 in cash and 500 shares of its common stock, representing aggregate cash and equity value of $ 10,000 . Following the effective date of the IPO, LifeStance Health Group consolidates the financial results of LifeStance TopCo, its wholly-owned subsidiaries and variable interest entities ("VIE's") and the financial statements for the periods prior to the IPO have been adjusted to combine the previously separate entities for presentation purposes. Prior to the IPO restructuring transactions, LifeStance Health Group had no operations.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTE 2 SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES There have been no changes in accounting policies during the three and nine months ended September 30, 2021 (Successor) from those disclosed in the annual consolidated financial statements for the period from April 13, 2020 to December 31, 2020 (Successor), the period from January 1, 2020 to May 14, 2020 (Predecessor) and the year ended December 31, 2019 (Predecessor) and the related notes. Basis of Presentation and Principles of Consolidation The Company has prepared the accompanying unaudited consolidated financial statements pursuant to the rules and regulations of the SEC regarding interim financial reporting, which include the accounts of LifeStance Health Group, LifeStance TopCo, its wholly-owned subsidiaries and VIEs in which LifeStance TopCo has an interest and is the primary beneficiary. Pursuant to these rules and regulations, the Company has omitted certain information and footnote disclosures it normally includes in its annual consolidated financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). All intercompany balances and transactions have been eliminated in consolidation. In management’s opinion, the Company has made all adjustments (consisting only of normal, recurring adjustments, except as otherwise indicated) necessary to fairly state its consolidated financial position, results of income/(loss) and comprehensive income/(loss) and cash flows. The Company’s interim period operating results do not necessarily indicate the results that may be expected for any other interim period or the full fiscal year. These financial statements and accompanying notes should be read in conjunction with the consolidated financial statements and notes thereto in the Company’s audited financial statements for the period from April 13, 2020 to December 31, 2020 (Successor), the period from January 1, 2020 to May 14, 2020 (Predecessor) and the year ended December 31, 2019 (Predecessor). As a result of the acquisition as further discussed in Note 3 , TPG Acquisition , periods prior to May 14, 2020 reflect financial statements of LifeStance Health, LLC. Periods subsequent to the acquisition and prior to the IPO and restructuring transactions reflect the financial statements of LifeStance TopCo. Periods subsequent to the IPO and restructuring transactions reflect the financial statements of LifeStance Health Group. All periods subsequent to the TPG Acquisition have been presented as the financial statements of LifeStance Health Group. Due to the change in the basis of accounting, the consolidated financial statements for the Predecessor and Successor periods are not necessarily comparable. Where applicable, a black line separates the Successor and Predecessor periods to highlight the lack of comparability. Use of Accounting Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make a number of estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Variable Interest Entities The Company evaluates its ownership, contractual and other interests in entities to determine if it has any variable interest in a VIE. These evaluations are complex and involve judgment and the use of estimates and assumptions based on available information. If the Company determines that an entity in which it holds a contractual or ownership interest is a VIE and that the Company is the primary beneficiary, the Company consolidates such entity in its consolidated financial statements. The primary beneficiary of a VIE is the party that meets both of the following criteria: (i) has the power to make decisions that most significantly affect the economic performance of the VIE; and (ii) has the obligation to absorb losses or the right to receive benefits that in either case could potentially be significant to the VIE. The Company performs ongoing reassessments of whether changes in the facts and circumstances regarding the Company’s involvement with a VIE will cause the consolidation conclusion to change. The Company acquires and operates certain care centers which are deemed to be Friendly-Physician Entities (“FPEs"). As part of an FPE acquisition, the Company acquires 100 % of the non-medical assets; however due to legal requirements the physician-owners must retain 100% of the equity interest. The Company’s agreements with FPEs generally consist of both a Management Service Agreement (“MSA”), which provides for various administrative and management services to be provided by the Company to the FPE, and Stock Transfer Restriction (“STR”) agreements with the physician-owners of the FPEs, which provide for the transition of ownership interests of the FPEs under certain conditions. The outstanding voting equity instruments of the FPEs are owned by the nominee shareholders appointed by the Company under the terms of the STR agreements. The Company has the right to receive income as an ongoing administrative fee, which effectively absorbs all of the residual interests and has also provided financial support through loans to the FPEs. The Company has exclusive responsibility for the provision of all non-medical services including facilities, technology and intellectual property required for the day-to-day operation and management of each of the FPEs, and makes recommendations to the FPEs in establishing the guidelines for the employment and compensation of the physicians and other employees of the FPEs. In addition, the STR agreements provide that the Company has the right to designate a person(s) to purchase the equity interest of the FPE for a nominal amount in the event of a succession event at the Company’s discretion. Based on the provisions of these agreements, the Company determined that the FPEs are VIEs due to the equity holder having insufficient capital at risk, and the Company has a variable interest in the FPEs. The contractual arrangements described above allow the Company to direct the activities that most significantly affect the economic performance of the FPEs. Accordingly, the Company is the primary beneficiary of the FPEs and consolidates the FPEs under the VIE model. Furthermore, as a direct result of nominal initial equity contributions by the physicians, the financial support the Company provides to the FPEs (e.g., loans) and the provisions of the contractual arrangements and nominee shareholder succession arrangements described above, the interests held by noncontrolling interest holders lack economic substance and do not provide them with the ability to participate in the residual profits or losses generated by the FPEs. Therefore, all income and expenses recognized by the FPEs are allocated to the Company members. The Company does not hold interests in any VIEs for which the Company is not deemed to be the primary beneficiary. As noted previously, the Company acquires 100% of the non-medical assets of the VIEs. The aggregate carrying values of the VIEs total assets and total liabilities not purchased by the Company but included on the consolidated balance sheets were not material at September 30, 2021 (Successor) and December 31, 2020 (Successor) . Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that the Company (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, the Company's unaudited consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. New Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) and also issued subsequent amendments to the initial guidance: ASU 2017-13, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2020-02, and ASU 2020-05 (collectively, “ASC 842”). ASC 842 outlines a comprehensive lease accounting model and supersedes the current lease guidance. The new guidance requires lessees to recognize lease liabilities and corresponding right-of-use assets for all leases with lease terms of greater than 12 months. It also changes the definition of a lease and expands the disclosure requirements of lease arrangements. ASC 842 is effective for private entities for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, inclusive of a one year deferral provided by ASU 2020-05. ASC 842 must be adopted using a modified retrospective method and early adoption is permitted. The Company is in the process of determining the impact of the adoption of ASC 842 on the Company’s consolidated financial statements and disclosures. However, given the Company’s current operating lease portfolio (see Note 16) the Company expects the recognition of the right-of-use assets and lease liabilities to have a material impact on the Company’s consolidated balance sheets. In June 2016, the FASB issued ASU 2016-13, Financial Instruments (Topic 326)-Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 requires an entity to utilize a new impairment model known as the current expected credit loss (“CECL”) model to estimate its lifetime “expected credit loss” and record an allowance that, when deducted from the amortized cost basis of the financial asset, presents the net amount expected to be collected on the financial asset. The CECL model is expected to result in more timely recognition of credit losses. ASU 2016-13 also requires new disclosures for financial assets measured at amortized cost, loans and available-for-sale debt securities. ASU 2016-13 is effective for private entities for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. ASU 2016-03 will apply as a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is adopted. The Company is in the process of evaluating the impact of the adoption of ASU 2016-13 on the Company’s consolidated financial statements and disclosures. In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. ASU 2019-12 is effective for private entities for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. Early adoption of the amendments is permitted, including adoption in any interim period for public business entities for periods for which financial statements have not yet been issued and all other entities for periods for which financial statements have not yet been made available for issuance. The Company is in the process of evaluating the impact of the adoption of ASU 2019-12 on the Company’s consolidated financial statements and disclosures. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”). This guidance provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions, subject to meeting certain criteria, that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. The amendments issued in March 2020 provide optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in ASU 2020-04 are effective for all entities as of March 12, 2020, through December 31, 2022. The Company is still evaluating the impact of adopting ASU 2020-04 on its consolidated financial statements and disclosures.

TPG Acquisition

TPG Acquisition	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
TPG Acquisition	NOTE 3 TPG ACQUISITION LifeStance TopCo was formed for the purpose of completing a merger transaction with affiliates of TPG and Lynnwood MergerSub, Inc. (“Merger Sub”) in order to carry on the business of LifeStance Health, LLC and subsidiaries. On April 14, 2020 , LifeStance Health Holdings, Inc. ("LifeStance Holdings") entered into a merger agreement among LifeStance Holdings, Lynnwood Intermediate Holdings, Inc., Merger Sub and Shareholder Representatives Services LLC (the "TPG Acquisition"). Immediately prior to the TPG Acquisition, LifeStance Health, LLC completed a reorganization pursuant to which the equity holders of LifeStance Health, LLC, including affiliates of Summit and affiliates of Silversmith (together with TPG and Summit, the Company’s “Principal Stockholders”) received a distribution of 100 % of the equity interests of LifeStance Health Holdings, a direct subsidiary of LifeStance Health, LLC, in complete redemption of their equity interests of LifeStance Health, LLC. Pursuant to the TPG Acquisition, (i) the historic equity holders of LifeStance Health, LLC contributed a portion of their units of LifeStance Holdings to LifeStance TopCo in exchange for equity interests of LifeStance TopCo and (ii) an indirect subsidiary of LifeStance TopCo, merged with and into LifeStance Holdings, with shareholders of LifeStance Holdings receiving cash consideration in connection with cancellation of the remainder of their shares. LifeStance TopCo has a controlling financial interest in LifeStance Holdings under the voting interest model. Therefore, the Company determined LifeStance TopCo would consolidate LifeStance Holdings. Further, the TPG Acquisition is considered to constitute a change in control of the LifeStance business, with LifeStance TopCo being deemed the acquirer. The TPG Acquisition has been accounted for using the acquisition method of accounting in accordance with ASC Topic 805, Business Combinations , which requires, among other things, that the assets acquired and liabilities assumed be recognized at their acquisition date fair values, with any excess of the consideration transferred over the estimated fair values of the identifiable net assets acquired recorded as goodwill. Immediately prior to the transaction, LifeStance Health, LLC was the reporting entity. As noted above, this entity will be considered the predecessor entity and the period prior to and including May 14, 2020 will be the predecessor period. LifeStance Health, LLC was subsequently dissolved as part of the transaction. Given that LifeStance TopCo is the accounting acquirer, it will be considered the successor entity and the successor period will begin on April 13, 2020. For the period from April 13, 2020 through May 13, 2020, the operations of LifeStance TopCo were limited to those incident to its formation and the TPG Acquisition, which were not significant. Pursuant to the merger, LifeStance TopCo issued 979,563 Class A-1 Units and 35,845 Class A-2 Units to certain of its equity holders, including TPG, Summit, Silversmith and members of the Company’s management team. Following the TPG Acquisition, the Company conducted its business through LifeStance TopCo and its consolidated subsidiaries, and subsequent to the IPO, the Company has conducted its business through LifeStance Health Group. All previously owned preferred units were converted into LifeStance TopCo common units upon the acquisition. Total consideration transferred consisted of the following: Cash consideration $ 670,941 Class A-1 units 345,978 Class A-2 units 35,845 Total consideration transferred $ 1,052,764 The total consideration of $ 1,052,764 consisted of $ 381,823 equity, including 345,978 Class A-1 Units and 35,845 Class A-2 Units at $ 1 per unit and $ 670,941 cash, including $ 4,500 cash placed in escrow, transaction fees, cash for debt repayment, and a working capital adjustment. The Company recorded the fair value of net assets acquired of $ 126,106 and recorded goodwill of $ 926,658 on May 14, 2020. Fair Values of Assets Acquired and Liabilities Assumed The following table summarizes the fair values of assets acquired and liabilities assumed as of the date of acquisition: Allocation of Purchase Price Amount Cash $ 27,224 Patient accounts receivable 25,152 Property and equipment 34,813 Prepaid expenses and other current assets 9,590 Deposits 1,766 Intangible assets 344,300 Goodwill 926,658 Total assets acquired 1,369,503 Accounts payable 3,456 Accrued payroll expenses 25,739 Other accrued expenses 48,655 Current portion of contingent consideration 5,861 Other current liabilities 1,848 Long-term debt, net 135,006 Other noncurrent liabilities 9,617 Contingent consideration, net of current portion 4,048 Deferred tax liability, net 82,509 Total liabilities assumed 316,739 Fair value of net assets $ 1,052,764 The fair value of assets and liabilities other than intangible assets approximate the carrying amount as of the acquisition date. The liquidity of receivables is based on contractual rates to payors. The identifiable intangible assets acquired include the LifeStance corporate trade name, trade names related to the regional clinics, non-competition agreements with the Company’s executives, and non-competition agreements with providers. In order to value trade names, the “relief-from-royalty” method was utilized. This method is based on the supposition that in lieu of ownership, the Company would be willing to pay a royalty in order to exploit the related benefits of the trade names. The value of the trade names was determined by discounting the inherent after-tax royalty savings associated with ownership or possession of the trade name over the expected useful life. The selected royalty rate (pre-tax) was based on an analysis of various factors, including an analysis of market data and comparable trade name agreements. As it pertains to the non-competition agreements, the “with-and-without” method was utilized to determine the value. Revenue with the non-competition agreement in place was based on the Company’s forecast. The values indicated from the “with-and-without” method were adjusted to reflect the ability, feasibility and desire for the partners to compete. Subsequent to the closing of the TPG Acquisition, there was an additional cash payment of $ 2,977 related to a working capital adjustment, which was accounted for as a measurement period adjustment (see Note 8). The following table summarizes the fair values of acquired intangible assets as of the date of the TPG Acquisition: Amount Useful Life Trade names – Corporate $ 235,500 22.5 years Trade names – Regional 22,900 5 years Non-competition agreements – Executives 77,500 4 years Non-competition agreements – Providers 8,400 5 years Total intangible assets $ 344,300 Pro Forma The Company’s unaudited pro forma revenue and net loss for the years ended December 31, 2020 and 2019 below have been prepared as if the TPG Acquisition occurred on January 1, 2019. Year ended Year ended Revenue $ 377,217 $ 212,518 Net loss $ ( 26,727 ) $ ( 52,463 ) Goodwill Goodwill represented the excess of the purchase price over the net identifiable assets acquired and liabilities assumed. Goodwill is primarily attributable to the assembled workforce, customer and payor relationships and anticipated synergies and economies of scale expected from the integration of the businesses. The synergies include certain cost savings, operating efficiencies, and other strategic benefits projected to be achieved as result of the acquisition. There is no tax-deductible goodwill from the TPG Acquisition. The transaction costs related to the TPG Acquisition were $ 32,942 , all of which were expensed as incurred.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Acquisitions	NOTE 4 ACQUISITIONS During the three months ended September 30, 2021 (Successor), the three months ended September 30, 2020 (Successor), the nine months ended September 30, 2021 (Successor), the period from April 13, 2020 to September 30, 2020 (Successor), and the period from January 1, 2020 to May 14, 2020 (Predecessor), the Company completed the acquisitions of 6 , 2 , 17 , 6 , and 6 outpatient mental health practices, respectively. The Company accounted for the acquisitions as business combinations using the acquisition method of accounting. The purchase price was allocated to the tangible and intangible assets acquired and liabilities assumed based on their estimated fair values as of the respective acquisition dates. Total consideration transferred for these acquisitions consisted of the following: Successor Predecessor Total consideration transferred Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Cash consideration $ 21,108 $ 8,049 $ 62,420 $ 31,674 $ 12,369 Cash consideration to be paid — — 325 — — Contingent consideration, at initial 2,775 1,035 5,514 4,226 3,788 Class A-2 common units 1 — — 1,486 4,500 — Debt consideration — — — — 500 Total consideration transferred $ 23,883 $ 9,084 $ 69,745 $ 40,400 $ 16,657 (1) Excludes 511 Class A-2 common units related to the promissory note (see “Debt consideration”) issued during the Predecessor period that was subsequently converted to equity during the Successor period. The results of the acquired businesses have been included in the Company’s consolidated financial statements beginning after their acquisition dates. It is impracticable to provide historical supplemental pro forma financial information along with revenue and earnings subsequent to the acquisition dates for acquisitions during the period due to a variety of factors, including access to historical information and the operations of acquirees being integrated within the Company shortly after closing and not operating as discrete entities within the Company’s organizational structure. Fair Values of Assets Acquired and Liabilities Assumed The following table summarizes the fair values of assets acquired and liabilities assumed as of the dates of acquisition: Successor Predecessor Allocation of Purchase Price Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Cash $ 820 $ 326 $ 2,868 $ 1,574 $ 238 Patient accounts receivable 963 822 4,762 4,204 1,344 Property and equipment 89 26 783 616 234 Prepaid expenses and other current 86 26 313 103 68 Deposits 73 15 164 207 87 Intangible assets 1,260 469 4,321 3,613 2,080 Goodwill 22,198 8,664 63,485 33,323 14,099 Total assets acquired 25,489 10,348 76,696 43,640 18,150 Current liabilities 1,606 1,264 6,951 3,240 1,493 Total liabilities assumed 1,606 1,264 6,951 3,240 1,493 Fair value of net assets $ 23,883 $ 9,084 $ 69,745 $ 40,400 $ 16,657 The following table summarizes the fair values of acquired intangible assets as of the dates of acquisition: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Regional trade names (1) $ 775 $ 266 $ 2,691 $ 2,304 $ 1,721 Non-Competition Agreements (2) 485 203 1,630 1,309 359 Total $ 1,260 $ 469 $ 4,321 $ 3,613 $ 2,080 (1) Useful lives for regional trade names are 5 years . (2) Useful lives for non-competition agreements are 5 years . Contingent Consideration Under the provisions of the acquisition agreements, the Company may pay additional cash consideration in the form of earnouts, contingent upon the acquirees achieving certain performance and operational targets including Earnings Before Interest, Taxes, Depreciation, and Amortization (“EBITDA”) measures and employee retention and growth (see Note 7). The following table summarizes the maximum contingent consideration based on the acquisition agreements: Successor Predecessor Contingent consideration Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Maximum contingent consideration $ 3,400 $ 1,275 $ 6,750 $ 11,575 $ 4,336

Intangible Assets

Intangible Assets	9 Months Ended
	Sep. 30, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets	NOTE 5 INTANGIBLE ASSETS Intangible assets consists of the following: September 30, 2021 (Successor) Gross Accumulated Net Weighted Regional trade names $ 33,168 $ ( 7,933 ) $ 25,235 5.0 LifeStance trade names 235,500 ( 14,474 ) 221,026 22.5 Non-competition agreements 91,719 ( 29,998 ) 61,721 4.2 Total intangible assets $ 360,387 $ ( 52,405 ) $ 307,982 December 31, 2020 (Successor) Gross Accumulated Net Weighted Regional trade names $ 30,477 $ ( 3,178 ) $ 27,299 5.0 LifeStance trade names 235,500 ( 6,624 ) 228,876 22.5 Non-competition agreements 90,089 ( 13,468 ) 76,621 4.1 Total intangible assets $ 356,066 $ ( 23,270 ) $ 332,796 Gross carrying amount is based on the fair value of the intangible assets determined at acquisitions. Total intangible asset amortization expense consists of the following: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Amortization expense $ 9,812 $ 9,260 $ 29,135 $ 13,929 $ 1,435

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment	NOTE 6 PROPERTY AND EQUIPMENT Property and equipment consists of the following: Successor September 30, 2021 December 31, 2020 Leasehold improvements $ 75,625 $ 39,586 Computers and peripherals 13,252 5,749 Furniture, fixtures and equipment 16,490 8,726 Medical equipment 3,868 2,143 Construction in process 19,890 7,577 Total $ 129,125 $ 63,781 Less: Accumulated depreciation ( 14,076 ) ( 4,432 ) Total property and equipment, net $ 115,049 $ 59,349 Depreciation expense consists of the following: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Depreciation expense $ 3,965 $ 1,650 $ 9,644 $ 2,413 $ 1,900

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	NOTE 7 FAIR VALUE MEASUREMENTS The Company measures its contingent consideration liability at fair value on a recurring basis using Level 3 inputs. The Company estimates the fair value of the contingent consideration liability based on the likelihood and timing of the contingent earn-out payments. The fair value is derived using valuation methodologies, such as a discounted cash flow model, and is not based on market exchange, dealer, or broker-traded transactions. This valuation incorporates certain assumptions and projections in determining the fair value assigned to such liability. The valuation methodology differs depending on the type of earn-out target. The following is the summary of the significant assumptions used for the fair value measurement of the contingent consideration liability as of September 30, 2021 (Successor) and December 31, 2020 (Successor). Valuation Technique Range of Significant Assumptions Successor September 30, 2021 Probability-weighted analysis Probability 25 % - 100 % based earn-outs (1) Discount rate 8.65 % - 8.68 % (1) During the second quarter of 2021, all contingent consideration liabilities previously estimated using a Monte Carlo Simulation EBITDA based earn-out technique transitioned, as deemed appropriate due to the remaining timing of the contracts and materiality of the underlying balances, to a probability-weighted analysis based on projected outcomes. Valuation Technique Range of Significant Assumptions Successor December 31, 2020 Monte Carlo Simulation Expected EBITDA Acquisition specific EBITDA based earn-outs Discount rate 16.15 % - 19.65 % Counter-party risk premium 8.46 % - 8.77 % Volatility 50 % Probability-weighted analysis Probability 25 % - 100 % FTE based earn-outs Discount rate 8.65 % - 8.68 % As of September 30, 2021 (Successor) and December 31, 2020 (Successor), the Company adjusted the fair value of the contingent consideration liability due to remeasurement at the reporting date. See Note 16 for discussion of payment of contingent consideration made related to prior year acquisitions, fair value adjustments, and a roll-forward of the contingent consideration balance from the prior year. The following table presents information about the Company’s liabilities that are measured at fair value on a recurring basis using the above input categories: September 30, 2021 (Successor) Level 1 Level 2 Level 3 Total Financial Instrument Contingent consideration liability $ — $ — $ 17,129 $ 17,129 December 31, 2020 (Successor) Level 1 Level 2 Level 3 Total Financial Instrument Contingent consideration liability $ — $ — $ 16,414 $ 16,414 At the closing of the TPG Acquisition (see Note 3), LifeStance TopCo recorded the acquired assets and assumed liabilities at their acquisition date fair values in accordance with ASC 805, Business Combinations . As disclosed in Note 4, the Company acquired several outpatient mental health practices during the three and nine months ended September 30, 2021 (Successor), the three months ended September 30, 2020 (Successor), the period from April 13, 2020 to September 30, 2020 (Successor) and the period from January 1, 2020 to May 14, 2020 (Predecessor) . The values of net tangible assets acquired, and the resulting goodwill and other intangible assets, were recorded at fair value using Level 3 inputs. The majority of the tangible assets acquired and liabilities assumed were recorded at their carrying values as of the respective dates of acquisition, as their carrying values approximated their fair values due to their short-term nature. The fair values of goodwill and other intangible assets acquired in these acquisitions were estimated with the assistance of a third-party valuation expert primarily based on the income approach. The income approach estimates fair value based on the present value of the cash flows that the assets are expected to generate in the future. The Company developed estimates for the expected future cash flows and discount rates used in the present value calculations. Other than assets acquired and liabilities assumed in these acquisitions, there were no material assets or liabilities measured at fair value on a nonrecurring basis during the periods presented.

GOODWILL

GOODWILL	9 Months Ended
	Sep. 30, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
GOODWILL	NOTE 8 GOODWILL Goodwill consists of the following: Amount Beginning balance as of April 13, 2020 (Successor) $ — TPG Acquisition (Note 3) 926,658 Measurement period adjustment (Note 3) 2,977 Business acquisitions 169,024 Ending balance as of December 31, 2020 (Successor) $ 1,098,659 Business acquisitions (Note 4) 63,485 Measurement period adjustments ( 2,133 ) Ending balance as of September 30, 2021 (Successor) $ 1,160,011 Goodwill represents the excess of the purchase price over the net identifiable assets acquired and liabilities assumed. Goodwill is primarily attributable to the assembled workforce, customer and payor relationships and anticipated synergies and economies of scale expected from the integration of the businesses. The synergies include certain cost savings, operating efficiencies, and other strategic benefits projected to be achieved as a result of the acquisition. All goodwill is deductible for tax purposes except for goodwill in connection with the TPG Acquisition.

LONG-TERM DEBT

LONG-TERM DEBT	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Long-term Debt	NOTE 9 LONG-TERM DEBT Long-term debt consists of the following: Successor September 30, 2021 December 31, 2020 Term loans $ 70,902 $ 283,950 Delayed Draw loans 90,659 89,870 Total long-term debt 161,561 373,820 Less: Current portion of long-term debt ( 1,323 ) ( 3,738 ) Less: Unamortized debt issue costs ( 2,791 ) ( 7,548 ) Total Long-Term Debt, Net of Current Portion $ 157,447 $ 362,534 The current portion of long-term debt is included within other current liabilities on the consolidated balance sheets. The fair value of long-term debt is based on the present value of future payments discounted by the market interest rates or the fixed rates based on current rates offered to the Company for debt with similar terms and maturities, which is a Level 2 fair value measurement. Long-term debt is presented at carrying value on the unaudited consolidated balance sheets. The fair value of long-term debt at September 30, 2021 (Successor) and December 31, 2020 (Successor) was $ 187,780 and $ 458,685 , respectively. In connection with the voluntary prepayment of $ 294,000 related to borrowings outstanding as of June 15, 2021, the Company recognized an extinguishment of debt charge within interest expense of $ 14,444 during the second quarter of 2021 related to the prepayment charge and the write-off of unamortized debt issuance costs. On May 14, 2020, in connection with the TPG Acquisition, the successor company entered into the Credit Agreement among LifeStance Holdings, Lynnwood Intermediate Holdings, Inc., Capital One, National Association, and each lender party thereto (the “May 2020 Credit Agreement”). The successor company did not assume any existing debt from the predecessor company. The May 2020 Credit Agreement resulted in the extinguishment of the March 2019 Credit Agreement recorded in the predecessor period, with the May 2020 Credit Agreement debt being treated as a new issuance of debt in the successor period. Unamortized debt issue costs of $ 2,689 were included in the calculation of extinguishment of debt. The Company borrowed $ 210,000 in term loans and $ 50,000 in delayed draw loans, payable in quarterly principal and interest payments, with a maturity date of May 14, 2026 . The interest rate is a variable interest rate determined at LIBOR plus 3.25 % to 3.75 %. The May 2020 Credit Agreement provides for an alternative rate structure to LIBOR. The term loans and delayed draw loans are collateralized by the tangible assets and stock pledge of the Company. On November 4, 2020, the Company amended the May 2020 Credit Agreement, adding an aggregate $ 115,000 in loan commitments by increasing the term loans by $ 75,000 and the delayed draw loans by $ 40,000 . The underlying terms of the agreement remained the same. In February 2021, the Company amended the May 2020 Credit Agreement, increasing the total delayed draw term loan commitment by $ 50,000 . The other terms of the agreement remained the same. On April 30, 2021, the Company amended the May 2020 Credit Agreement, adding an aggregated $ 70,000 in loan commitments, increase the term loans by $ 20,000 and the delayed draw term loan commitment by $ 50,000 . The terms of the agreement otherwise remained the same. The May 2020 Credit Agreement requires the Company to maintain compliance with certain restrictive financial covenants related to earnings, leverage ratios, and other financial metrics. The Company was in compliance with all debt covenants at September 30, 2021 (Successor). Interest expense, including prepayment charge, consists of the following: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Interest expense $ 3,503 $ 6,421 $ 35,309 $ 11,983 $ 3,020 Future principal payments on long-term debt are as follows: Amount Remainder of 2021 $ 331 2022 1,323 2023 1,323 2024 1,323 2025 1,323 Thereafter 155,938 Total $ 161,561 Revolving Loan Under the May 2020 Credit Agreement, the Company has a revolving loan commitment from Capital One in the amount of $ 20,000 . Any borrowing on the revolving loan is due in full on May 14, 2025 . The revolving loan can be drawn upon at an interest rate equal to LIBOR plus 4.50 % to 4.75 %, depending on certain financial ratios. The unused revolving loan incurs a commitment fee of 0.5 % per annum. There are no amounts outstanding on the revolving loan as of September 30, 2021 (Successor) .

TOTAL REVENUES

TOTAL REVENUES	9 Months Ended
	Sep. 30, 2021
Revenues [Abstract]
TOTAL REVENUES	NOTE 10 TOTAL REVENUES The Company’s total revenues are dependent on a series of contracts with third-party payors, which is typical for providers in the health care industry. The Company has determined that the nature, amount, timing and uncertainty of revenue and cash flows are affected by the payor mix with third-party payors, which have different reimbursement rates. The payor mix of fee-for-service revenue from patients and third-party payors consists of the following: Successor Three Months Ended Three Months Ended Nine Months Ended Amount % of Total Revenue Amount % of Total Revenue Amount % of Total Revenue Commercial $ 158,035 91 % $ 90,810 89 % $ 433,684 91 % Government 8,731 5 % 4,782 5 % 20,942 4 % Self-pay 5,948 3 % 4,416 4 % 19,230 4 % Total patient service revenue 172,714 99 % 100,008 98 % 473,856 99 % Nonpatient service revenue 1,121 1 % 1,974 2 % 3,660 1 % Total $ 173,835 100 % $ 101,982 100 % $ 477,516 100 % Successor Predecessor April 13 to January 1 to May 14, 2020 Amount % of Total Revenue Amount % of Total Revenue Commercial $ 129,983 88 % $ 98,146 88 % Government 7,468 5 % 5,411 5 % Self-pay 6,703 5 % 4,821 4 % Total patient service revenue 144,154 98 % 108,378 97 % Nonpatient service revenue 3,281 2 % 3,283 3 % Total $ 147,435 100 % $ 111,661 100 % Among the commercial payors, five insurance companies comprise the following percentage of revenue. Three payors individually exceed 10 % of the Company’s revenue for the three months ended September 30, 2021 (Successor), the three months ended September 30, 2020 (Successor), the nine months ended September 30, 2021 (Successor), the period from April 13, 2020 to September 30, 2020 (Successor) , and the period from January 1, 2020 to May 14, 2020 (Predecessor). Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Top five commercial payors 63 % 69 % 63 % 67 % 67 % Top one payor 19 % 23 % 19 % 23 % 23 % Top two payor 18 % 18 % 17 % 19 % 19 % Top three payor 12 % 13 % 13 % 13 % 11 %

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 11 INCOME TAXES The benefit for income taxes is as follows: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Benefit from income taxes $ 8,751 $ 1,074 $ 15,300 $ 2,444 $ 2,319 The effective tax rates are as follows: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Effective tax rate 6.8 % 24.6 % 7.1 % 24.2 % 8.5 % The difference between the Company’s effective tax rate and the U.S. statutory tax rate of 21 % was primarily due to state taxes and permanent differences. The Company regularly evaluates the realizability of its deferred tax assets and establishes a valuation allowance if it is more likely than not that some or all the deferred tax assets will not be realized. No valuation allowance was recognized as of September 30, 2021 (Successor) or December 31, 2020 (Successor) .

Redeemable Convertible Preferre

Redeemable Convertible Preferred Units	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Units	NOTE 12 REDEEMABLE CONVERTIBLE PREFERRED UNITS On July 20, 2017, LifeStance Health, LLC executed an Amended and Restated Limited Liability Company Agreement which established the terms of the Series A-1 redeemable convertible preferred units (“Series A-1 Preferred Units”) and Series A redeemable convertible preferred units (“Series A Preferred Units”) (collectively, referred to as the “Preferred Units”), which were issued to various investors and employees of the Company. In connection with the TPG Acquisition, the holders of LifeStance Health, LLC’s Preferred Units exchanged 100 % of their units for equity interests in LifeStance Holdings and the historic Preferred Unit holders contributed all of their interest in LifeStance Holdings to LifeStance TopCo, in exchange for LifeStance TopCo’s Class A-1 Common Units and Class A-2 Common Units. The Preferred Units were adjusted through a reverse unit split. The Preferred Units are classified as mezzanine equity in the consolidated balance sheets and remeasured to their redemption value at each reporting date. The Series A Preferred Units’ redemption value is equal to its issuance price; as such, no remeasurement adjustment amount was recorded for the period ended May 14, 2020. The Series A-1 Preferred Units’ redemption value is equal to the greater of i) fair value at the redemption date, and ii) the sum of the issuance price plus any accumulated but unpaid dividends. Changes in the carrying amount of the Series A-1 Preferred Units will be charged against retained earnings (or additional paid-in capital in the absence of retained earnings until exhausted, at which point any remainder would increase accumulated deficit). The table below includes the number of authorized units and issued units, as well as the issuance price, liquidation preference and initial carrying amount of the Preferred Units immediately prior to the TPG Acquisition, which occurred on May 14, 2020. Year of Authorized Issued Units Issuance Price Liquidation Initial Carrying Unit Series Series A-1 2017 110,898 87,000 $ 1.00 $ 106,978 $ 87,000 2018 110,898 22,838 1.00 26,568 22,838 109,838 $ 133,546 $ 109,838 Series A 2017 23,600 11,741 $ 1.00 $ 14,504 $ 11,741 2018 23,600 1,500 1.50 2,536 2,250 2019 23,600 2,885 2.00 6,276 5,770 16,126 $ 23,316 $ 19,761 As discussed above, pursuant to the TPG Acquisition (see Note 3), the historic holders of Series A and Series A-1 Preferred Units exchanged all the units for equity interests in LifeStance Holdings, and subsequently exchanged equity interests for the successor’s Class A-1 Units and Class A-2 Units. See Note 14 for more details on the exchange.

Stock And Unit-Based Compensati

Stock And Unit-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
STOCK AND UNIT-BASED COMPENSATION	NOTE 13 STOCK AND UNIT-BASED COMPENSATION Post-IPO Equity Awards 2021 Equity Incentive Plan Effective June 9, 2021, the Company’s Board of Directors (the "Board") and its stockholders as of that date adopted and approved the LifeStance Health Group, Inc. 2021 Equity Incentive Plan (the “2021 Equity Incentive Plan”). All equity-based awards subsequent to June 9, 2021 will be granted under the 2021 Plan. The 2021 Equity Incentive Plan permits the grant of awards or restricted or unrestricted common stock, stock options, stock appreciation rights, restricted stock units, performance awards, and other stock-based awards to employees and directors of, and consultants and advisors to, the Company and its affiliates. The maximum number of shares of the Company’s common stock that may be delivered in satisfaction of awards under the 2021 Equity Incentive Plan is 47,037 shares. The share pool will automatically increase on January 1 of each year beginning in 2022 and continuing through and including 2031 by the lesser of (i) five percent of the number of shares of the Company’s common stock outstanding as of the close of business on the immediately preceding December 31 and (ii) the number of shares determined by the Board on or prior to such date for such year. Restricted Stock The restricted stock was issued as part of the Organizational Transactions (see Note 1). The following is a summary of restricted stock transactions as of and for the three and nine months ended September 30, 2021 (Successor): Unvested Shares Weighted-Average Grant Date Unvested, June 30, 2021 (Successor) 30,766 $ 11.98 Converted — — Granted — — Vested ( 17 ) 12.01 Unvested, September 30, 2021 (Successor) 30,749 $ 11.98 Unvested Shares Weighted-Average Grant Date Unvested, June 9, 2021 (Successor) — $ — Converted 30,766 11.98 Granted — — Vested ( 17 ) 12.01 Unvested, September 30, 2021 (Successor) 30,749 $ 11.98 Restricted Stock Units The restricted stock units (“RSUs”) were granted in connection with the IPO and subsequent to the IPO. RSUs are accounted for as equity using the fair value method, which requires measurement and recognition of compensation expense for all awards granted to employees, directors and consultants based upon the grant-date fair value. The following is a summary of RSU transactions as of and for the three and nine months ended September 30, 2021 (Successor): Unvested Shares Weighted-Average Grant Date Outstanding, June 30, 2021 (Successor) 6,128 $ 18.00 Converted — — Granted 80 12.87 Vested — — Outstanding, September 30, 2021 (Successor) 6,208 $ 17.93 Unvested Shares Weighted-Average Grant Date Outstanding, June 9, 2021 (Successor) — $ — Converted — — Granted 6,208 17.93 Vested — — Outstanding, September 30, 2021 (Successor) 6,208 $ 17.93 The Company recognized $ 120,689 and $ 149,674 in stock-based compensation expense related to restricted stock and RSUs for the three and nine months ended September 30, 2021 (Successor), respectively, within general and administrative expenses in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss). As of September 30, 2021 (Successor), the Company had $ 331,241 in unrecognized compensation expense related to all non-vested awards (restricted stock and RSUs) that will be recognized over the weighted-average remaining service period of 1.9 years. 2021 Employee Stock Purchase Plan Effective June 9, 2021, the Board and its stockholders as of that date adopted and approved the LifeStance Health Group, Inc. 2021 Employee Stock Purchase Plan (the “ESPP”). The ESPP permits the grant to eligible employees of the Company and its participating subsidiaries of options to purchase shares of the Company’s common stock. The aggregate number of shares of the Company common stock available for purchase pursuant to the exercise of options under the ESPP is 6,817 shares, plus an automatic annual increase, as of January 1 of each year beginning in 2022 and continuing through and including 2031, equal to the lesser of (i) one percent of the number of shares of the Company’s common stock outstanding as of the close of business on the immediately preceding December 31 and (ii) the number of shares determined by the Board on or prior to such date for such year, up to a maximum of 42,500 shares of the Company’s common stock in the aggregate. The ESPP allows participants to purchase common stock through payroll deductions of up to 15 % of their eligible compensation. The purchase price of the shares will be 85 % of the lower of the fair market value of the Company’s common stock on the grant date or the exercise date. The ESPP will generally be implemented by a series of separate offerings referred to as “Option Periods”. Unless otherwise determined by the administrator, the Option Periods will be successive periods of approximately six months commencing on the first business day in January and July of each year, anticipated to be on or around January 1 and July 1, and ending approximately six months later on the last business day in June or December, as applicable, of each year, anticipated to be on or around June 30 and December 31. The last business day of each Option Period will be an “Exercise Date”. The administrator may change the Exercise Date, the commencement date, the ending date and the duration of each Option Period, in each case, to the extent permitted by Section 423 of the Internal Revenue Code; provided, however, that no option may be exercised after 27 months from its grant date. As of September 30, 2021 (Successor) , no shares of common stock have been purchased under the Company’s ESPP. Pre-IPO Equity Awards Class C Units and Class A Units (Predecessor) For the period from January 1, 2020 to May 14, 2020 and prior (Predecessor), the Board of Directors of LifeStance Health, LLC issued Class C Units and Class A Units options, which represented options to purchase membership units in LifeStance Health, LLC. All Class C Units and Class A Units options were fully vested and exercised as of May 14, 2020, and all holders were granted LifeStance TopCo Class A-1 Units upon the TPG Acquisition occurring. No options to purchase Class C Units or Class A Units were outstanding at May 14, 2020. On the grant date, recipients of the Class C Units and Class A Units purchased for cash the units at their fair market value. The Company recorded total unit-based compensation expense of $ 0 for the period from January 1, 2020 to May 14, 2020 (Predecessor) related to both Class C Units and Class A Units. Class B Profits Interests Units (Successor) On May 14, 2020, the Board of Directors of LifeStance TopCo adopted a form of Partnership Interest Award Agreement (“Award Agreement”). From May 14, 2020 through June 9, 2021 (Successor), the Company granted awards in the form of Profits Interests Units to employees, officers and directors on terms set forth in the Award Agreement. These Profits Interests represented profits interest ownership in the Company tied solely to the accretion, if any, in the value of the Company following the date of issuance of such Profits Interests. Profits Interests participated in any increase of the Company value related to their profits interests after the hurdle value had been achieved. A maximum of 179,190 Class B Profits Interests Units were available to be granted under the Award Agreement. Awards were granted on a discretionary basis and were subject to the approval of the Board of Directors of LifeStance TopCo. The Company granted 152,865 Class B Profits Interests Units awards from May 14, 2020 through June 9, 2021 (Successor). Holders of the Profits Interests Units received distributions (other than tax distributions) only upon a liquidity event, as defined, that exceeded a threshold equivalent to the fair value of the Company, as determined by the Company’s Board, at the grant date. All awards included a repurchase option at the election of the Company for the vested portion upon termination of employment or service and any unvested awards would be forfeited. Profits Interests Units are accounted for as equity using the fair value method, which requires the measurement and recognition of compensation expense for all profit interest-based payment awards made to the holders based upon the grant-date fair value. The Company has concluded that both the Service-Vesting Units and the Performance-Vesting Units are subject to a market condition and has assessed the market condition as part of its determination of the grant date fair value. Accordingly, the Company determined the fair value of each award on the date of grant using a Monte Carlo simulation model with the following assumptions used for the grants issued for the nine months ended September 30, 2021 (Successor), for the three months ended September 30, 2020 (Successor) and for the period from April 13, 2020 to September 30, 2020 (Successor): Successor Nine Months Ended Three Months Ended September 30, 2020 April 13 to Risk-free rate 0.14 % 0.20 % 0.20 % Volatility 80.00 % 40.00 % 40.00 % Time to liquidity event (years) 2.00 3.00 3.00 Discount for lack of marketability (DLOM) — 20.00 % 20.00 % The volatility assumption used in the Monte Carlo simulation model is based on the expected volatility of public companies in similar industries, adjusted to reflect the differences between the Company and other public companies in size, resources, time in industry, and breadth of service offerings. In connection with the IPO, the outstanding Profits Interests were contributed to LifeStance Health Group in exchange for common stock, including restricted stock. The following is a summary of Class B Profits Interests Units for the nine months ended September 30, 2021 (Successor), for the three months ended September 30, 2020 (Successor) and for the period from April 13, 2020 to September 30, 2020 (Successor): Class B Profits Weighted- Outstanding, December 31, 2020 143,343 $ 0.13 Granted 9,522 0.16 Forfeited ( 245 ) 0.13 Converted ( 152,620 ) 0.13 Outstanding, September 30, 2021 (Successor) — $ — Class B Profits Weighted- Outstanding, June 30, 2020 134,855 $ 0.13 Granted 627 0.13 Outstanding, September 30, 2020 (Successor) 135,482 $ 0.13 Class B Profits Weighted- Outstanding, April 13, 2020 — $ — Granted 135,482 0.13 Outstanding, September 30, 2020 (Successor) 135,482 $ 0.13 There were no Class B Profits Interests Units outstanding as of June 30, 2021 (Successor) and September 30, 2021 (Successor). Stock and Unit-Based Compensation Expense The Company recognized unit-based compensation expense related to the Class B Profits Interests within general and administrative expenses in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss) as follows: Successor Three Months Ended Nine Months Ended April 13 to Unit-based compensation expense $ 573 $ 1,135 $ 865 As part of the Organizational Transactions, the Class B Profits Interests Units that were subject to vesting over a period of continuous employment or service and were unvested upon the Organizational Transactions were converted to restricted stock that vests over a modified requisite service period of three years. The unvested Class B Profits Interests Units that were subject to vesting upon the sale of the Company were converted to restricted stock that were modified to add both a market and service condition and vest between six months and two years following the IPO. These awards, which were subject to vesting upon the sale of the Company, were deemed improbable until June 10, 2021 when the IPO occurred. As a result of this vesting condition being deemed probable on the date of the IPO, the equity holders of these awards received 30,766 shares of common stock issued as restricted stock that are subject to market and service-based vesting conditions. The stock compensation expense recorded for these modifications to convert the Class B Profits Interests Units to restricted stock, acceleration of vesting terms, and the additional RSUs granted at the time of IPO is included in the $ 149,674 of stock-based compensation expense for the nine months ended September 30, 2021 (Successor) . This amount was recognized within general and administrative expenses in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss).

Stockholders' Equity Members' D

Stockholders' Equity Members' Deficit	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Stockholders and Member Equity	NOTE 14 STOCKHOLDERS’/MEMBERS’ EQUITY Common Stock – Post-IPO As discussed in Note 1, upon completion of the Company’s IPO in June 2021, the Company sold 32,800 shares of common stock at an offering price of $ 18.00 per share. In connection with the IPO, the Company increased its authorized shares from 1 to 800,000 shares of common stock, par value $ 0.01 per share. The Company’s common stock/units consisted of the following common units and common stock as of the periods ended September 30, 2021 (Successor) and December 31, 2020 (Successor): Redeemable Class A-1 Units Class A-2 Units Class B Units Common Stock Total Balance as of April 13, — — — — — — Issued 35,000 959,563 49,946 — — 1,044,509 Balance as of 35,000 959,563 49,946 — — 1,044,509 Issued — — 1,687 — — 1,687 Vested Class B Profits — — — 17,920 — 17,920 Conversion of pre-IPO ( 35,000 ) ( 959,563 ) ( 51,633 ) ( 17,920 ) 340,849 ( 723,267 ) Initial Public Offering — — — — 32,800 32,800 Endowment to the — — — — 500 500 Balance as of September — — — — 374,149 374,149 Common Units - Pre-IPO Upon the closing of the TPG Acquisition, the Company initiated two share exchanges for all outstanding shares, including Class A and Class C Units, as well as Series A and Series A-1 Preferred Units. Subsequent to the share exchanges, holders of the units received cash consideration for a portion of their units, and the remaining units were exchanged for Class A-1 and Class A-2 units of LifeStance TopCo based on a predetermined exchange ratio. There were approximately 345,978 and 35,845 Class A-1 and Class A-2 units outstanding, respectively, as a result of the exchange of equity on May 14, 2020. No Class A Units or Class C Units were outstanding after the TPG Acquisition as a result of the conversion. The chief executive officer (“CEO”) had 35,000 redeemable Class A units outstanding prior to the completion of the IPO. The CEO had the right, upon termination for any reason other than proper cause, to put his redeemable Class A units back to the partnership at fair value (“Put Right”). The CEO (or permitted transferee) shall have this Put Right also upon death or disability. As this was both outside of the Company’s control and probable to eventually occur, the redeemable Class A units subject to this Put Right were classified as mezzanine equity and carried at fair value (i.e., redemption price). There was a change to the fair value during the period from January 1 to June 9, 2021 (Successor) of $ 36,750 , respectively, resulting from a change in the probability assumption of an IPO. On June 9, 2021, the redeemable Class A units were converted into 10,234 shares of the Company’s common stock. Class A-1 Common Units had equal voting rights. Class A-2 and Class B Common Units were nonvoting units. See Note 13 for discussion regarding Class B Units outstanding pre-IPO. Preferred Stock In connection with the Company’s IPO, the Company authorized the issuance of 25,000 shares of its preferred stock, par value $ 0.01 per share. There are no shares of preferred stock outstanding as of September 30, 2021 (Successor) .

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	NOTE 15 RELATED PARTY TRANSACTIONS The Company leases 40 office facilities under operating leases with clinicians expiring through 2034 . The leases provide for monthly minimum rent payments, and some include renewal options for additional terms. Minimum rent payments under operating leases are recognized on a straight-line basis over the term of the lease. Total related-party rent expense included in center costs in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss) amounted to: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Rent expense $ 809 $ 262 $ 2,006 $ 369 $ 388 A summary of non-cancelable future minimum operating lease payments under these leases as of September 30, 2021 (Successor) is as follows: Amount Remainder of 2021 $ 761 2022 2,973 2023 2,688 2024 2,415 2025 2,333 Thereafter 1,501 Total $ 12,671 In addition, management fees to TPG and certain executives of the Company were identified as related party transactions. As a result of the Company’s IPO, the Company incurred a termination fee of $ 1,213 under its management services agreement in the second quarter of 2021, and no management fees were recognized in the third quarter of 2021. Total related-party management fees amounted to: Successor Predecessor Three Months Ended Nine Months Ended April 13 to January 1 to Management fees $ 44 $ 1,445 $ 60 $ 14

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	NOTE 16 COMMITMENTS AND CONTINGENCIES Contingent Consideration relating to Prior Acquisitions For the three and nine months ended September 30, 2021 (Successor), there were post-closing payments contingent upon the future performance of the Company’s recently acquired targets achieving certain agreed-upon performance metrics. Contingent consideration is recorded at fair value and was recognized in the purchase price allocation (see Note 4) of the acquired company. The following table presents changes to the Company’s contingent consideration balance: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Beginning balance $ 14,123 $ 10,951 $ 16,414 $ — $ 25,536 Additions related to TPG Acquisition — — — 9,909 — Additions related to acquisitions 2,775 1,035 5,514 4,226 3,788 Payments of contingent consideration ( 675 ) ( 100 ) ( 6,262 ) ( 2,300 ) ( 19,093 ) Loss (gain) on remeasurement 906 ( 89 ) 1,463 ( 38 ) ( 322 ) Ending balance $ 17,129 $ 11,797 $ 17,129 $ 11,797 $ 9,909 Leases with Third Parties The Company leases its office facilities under operating leases expiring through 2029 . The leases provide for monthly minimum rent payments, and some include renewal options for additional terms. Minimum rent payments under operating leases are recognized on a straight-line basis over the term of the lease. Total third-party rent expense amounted to as follows in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss): Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Center costs $ 8,302 $ 4,484 $ 21,878 $ 6,779 $ 4,082 General and administrative expenses 127 122 655 183 128 Total rent expense $ 8,429 $ 4,606 $ 22,533 $ 6,962 $ 4,210 A summary of non-cancellable future minimum third-party operating lease payments under these leases as of September 30, 2021 (Successor) is as follows: Amount Remainder of 2021 $ 6,391 2022 26,183 2023 25,093 2024 21,140 2025 17,072 Thereafter 33,724 Total $ 129,603 Professional Liability Insurance The medical malpractice insurance coverage is subject to a $ 8,000 per claim limit and an annual aggregate limit of $ 12,000 per clinician. Should the claims-made policy not be renewed or replaced with equivalent insurance, claims based on occurrences during its term, but reported subsequently, would be uninsured. The Company is not aware of any unasserted claims, unreported incidents, or claims outstanding that are expected to exceed malpractice insurance coverage limits as of September 30, 2021 (Successor). Health Care Industry The health care industry is subject to numerous laws and regulations of federal, state, and local governments. These laws and regulations include, but are not necessarily limited to, matters such as licensure, accreditation, and government health care program participation requirements, reimbursement for patient services, and Medicare fraud and abuse. Recently, government activity has increased with respect to investigations and allegations concerning possible violations of fraud and abuse statutes and regulations by health care providers. Violation of these laws and regulations could result in expulsion from government health care programs together with imposition of significant fines and penalties, as well as significant repayments for patient services billed. Laws and regulations concerning government programs, including Medicare and Medicaid, are complex and subject to varying interpretation. As a result of investigations by governmental agencies, various health care companies have received requests for information and notices regarding alleged noncompliance with those laws and regulations, which, in some instances, have resulted in companies entering into significant settlement agreements. Compliance with such laws and regulations may also be subject to future government review and interpretation as well as significant regulatory action, including fines, penalties, and potential exclusion from the related programs. There can be no assurance that regulatory authorities will not challenge the Company’s compliance with these laws and regulations, and it is not possible to determine the impact (if any) such claims or penalties would have upon the Company. In addition, the contracts the Company has with commercial payors also provide for retroactive audit and review of claims. Management believes that the Company is in substantial compliance with fraud and abuse as well as other applicable government laws and regulations. While no regulatory inquiries have been made, compliance with such laws and regulations is subject to government review and interpretation, as well as regulatory actions unknown or unasserted at this time. In response to the COVID-19 pandemic, state and federal regulatory authorities loosened or removed a number of regulatory requirements in order to increase the availability of telehealth services. For example, many state governors issued executive orders permitting physicians and other health care professionals to practice in their state without any additional licensure or by using a temporary, expedited or abbreviated licensure process so long as they hold a valid license in another state. In addition, changes were made to the Medicare and Medicaid programs (through waivers and other regulatory authority) to increase access to telehealth services by, among other things, increasing reimbursement, permitting the enrollment of out of state providers and eliminating prior authorization requirements. It is uncertain how long these COVID-19 related regulatory changes will remain in effect and whether they will continue beyond this public health emergency period. Management does not believe that the Company’s operations or results will be materially adversely affected by a return to the status quo from a regulatory perspective. General Contingencies The Company is exposed to various risks of loss related to torts; theft of, damage to and destruction of assets; errors and omissions, injuries to employees, and natural disasters. These risks are covered by commercial insurance purchased from independent third parties. There has been no significant reduction in insurance coverage from the previous year in any of the Company’s policies. Litigation The Company may be involved from time-to-time in legal actions relating to the ownership and operations of its business. In management’s opinion, the liabilities, if any, that may ultimately result from such legal actions are not expected to have a material adverse effect on the financial position, results of operations, or cash flows of the Company.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	NOTE 17 NET LOSS PER SHARE Prior to the IPO, as discussed in Note 1, the partnership interests of LifeStance TopCo included Redeemable Class A, Class A common and Class B units. The Class B Units were intended to be "profits interests" for U.S. federal income tax purposes. Prior to the IPO, each of the holders of partnership interests in LifeStance TopCo contributed its partnership interest to LifeStance Health Group in exchange for shares of common stock (including shares of common stock issued as restricted stock subject to vesting) of LifeStance Health Group, with no changes in relative equity holder rights, rank or value before or after this exchange. As a result, the LifeStance TopCo equity exchange of common units was considered equivalent to a stock split and requires retrospective treatment for net loss per share purposes. All share and per share information has been retroactively adjusted to reflect the equity exchange for all periods presented. Vested Class B Profits Interests Units outstanding prior to the equity exchange were considered compensatory arrangements that were settled with shares of common stock at the time of the exchange and have been included as outstanding shares subsequent to that date. The following table presents the calculation of basic and diluted net income/(loss) per share (“EPS”) for the Company’s common shares (on an as-converted basis): Successor Three Months Ended Three Months Ended Nine Months Ended April 13 to Net loss available to common $ ( 120,452 ) $ ( 3,294 ) $ ( 235,917 ) $ ( 7,636 ) Weighted-average shares used to compute 343,394 302,657 321,283 300,799 Net loss per share, basic and diluted $ ( 0.35 ) $ ( 0.01 ) $ ( 0.73 ) $ ( 0.03 ) The Company has issued potentially dilutive instruments in the form of restricted stock and the RSUs. The Company did not include any of these instruments in its calculation of diluted loss per share (on an as-converted basis) for the three and nine months ended September 30, 2021 (Successor), the three months ended September 30, 2020 (Successor) and for the period from April 13, 2020 to September 30, 2020 (Successor) because to include them would be anti-dilutive due to the Company’s net loss during the period. See Note 13 for the issued, vested and unvested Class B Profits Interests Units, restricted stock and RSUs.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	NOTE 18 SUBSEQUENT EVENTS Acquisitions Subsequent to September 30, 2021, the Company completed acquisitions of several outpatient mental health practices. The allocation of purchase price, including any fair value of contingent consideration, to the assets acquired and liabilities assumed as of the acquisition dates have not been completed. For acquisitions completed subsequent to September 30, 2021, total contractual consideration included cash consideration of $ 34,973 , funded through credit facility financing, and contingent consideration with a maximum value of $ 2,507 .

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The Company has prepared the accompanying unaudited consolidated financial statements pursuant to the rules and regulations of the SEC regarding interim financial reporting, which include the accounts of LifeStance Health Group, LifeStance TopCo, its wholly-owned subsidiaries and VIEs in which LifeStance TopCo has an interest and is the primary beneficiary. Pursuant to these rules and regulations, the Company has omitted certain information and footnote disclosures it normally includes in its annual consolidated financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). All intercompany balances and transactions have been eliminated in consolidation. In management’s opinion, the Company has made all adjustments (consisting only of normal, recurring adjustments, except as otherwise indicated) necessary to fairly state its consolidated financial position, results of income/(loss) and comprehensive income/(loss) and cash flows. The Company’s interim period operating results do not necessarily indicate the results that may be expected for any other interim period or the full fiscal year. These financial statements and accompanying notes should be read in conjunction with the consolidated financial statements and notes thereto in the Company’s audited financial statements for the period from April 13, 2020 to December 31, 2020 (Successor), the period from January 1, 2020 to May 14, 2020 (Predecessor) and the year ended December 31, 2019 (Predecessor). As a result of the acquisition as further discussed in Note 3 , TPG Acquisition , periods prior to May 14, 2020 reflect financial statements of LifeStance Health, LLC. Periods subsequent to the acquisition and prior to the IPO and restructuring transactions reflect the financial statements of LifeStance TopCo. Periods subsequent to the IPO and restructuring transactions reflect the financial statements of LifeStance Health Group. All periods subsequent to the TPG Acquisition have been presented as the financial statements of LifeStance Health Group. Due to the change in the basis of accounting, the consolidated financial statements for the Predecessor and Successor periods are not necessarily comparable. Where applicable, a black line separates the Successor and Predecessor periods to highlight the lack of comparability.
Use of Accounting Estimates	Use of Accounting Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make a number of estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Variable Interest Entities	Variable Interest Entities The Company evaluates its ownership, contractual and other interests in entities to determine if it has any variable interest in a VIE. These evaluations are complex and involve judgment and the use of estimates and assumptions based on available information. If the Company determines that an entity in which it holds a contractual or ownership interest is a VIE and that the Company is the primary beneficiary, the Company consolidates such entity in its consolidated financial statements. The primary beneficiary of a VIE is the party that meets both of the following criteria: (i) has the power to make decisions that most significantly affect the economic performance of the VIE; and (ii) has the obligation to absorb losses or the right to receive benefits that in either case could potentially be significant to the VIE. The Company performs ongoing reassessments of whether changes in the facts and circumstances regarding the Company’s involvement with a VIE will cause the consolidation conclusion to change. The Company acquires and operates certain care centers which are deemed to be Friendly-Physician Entities (“FPEs"). As part of an FPE acquisition, the Company acquires 100 % of the non-medical assets; however due to legal requirements the physician-owners must retain 100% of the equity interest. The Company’s agreements with FPEs generally consist of both a Management Service Agreement (“MSA”), which provides for various administrative and management services to be provided by the Company to the FPE, and Stock Transfer Restriction (“STR”) agreements with the physician-owners of the FPEs, which provide for the transition of ownership interests of the FPEs under certain conditions. The outstanding voting equity instruments of the FPEs are owned by the nominee shareholders appointed by the Company under the terms of the STR agreements. The Company has the right to receive income as an ongoing administrative fee, which effectively absorbs all of the residual interests and has also provided financial support through loans to the FPEs. The Company has exclusive responsibility for the provision of all non-medical services including facilities, technology and intellectual property required for the day-to-day operation and management of each of the FPEs, and makes recommendations to the FPEs in establishing the guidelines for the employment and compensation of the physicians and other employees of the FPEs. In addition, the STR agreements provide that the Company has the right to designate a person(s) to purchase the equity interest of the FPE for a nominal amount in the event of a succession event at the Company’s discretion. Based on the provisions of these agreements, the Company determined that the FPEs are VIEs due to the equity holder having insufficient capital at risk, and the Company has a variable interest in the FPEs. The contractual arrangements described above allow the Company to direct the activities that most significantly affect the economic performance of the FPEs. Accordingly, the Company is the primary beneficiary of the FPEs and consolidates the FPEs under the VIE model. Furthermore, as a direct result of nominal initial equity contributions by the physicians, the financial support the Company provides to the FPEs (e.g., loans) and the provisions of the contractual arrangements and nominee shareholder succession arrangements described above, the interests held by noncontrolling interest holders lack economic substance and do not provide them with the ability to participate in the residual profits or losses generated by the FPEs. Therefore, all income and expenses recognized by the FPEs are allocated to the Company members. The Company does not hold interests in any VIEs for which the Company is not deemed to be the primary beneficiary. As noted previously, the Company acquires 100% of the non-medical assets of the VIEs. The aggregate carrying values of the VIEs total assets and total liabilities not purchased by the Company but included on the consolidated balance sheets were not material at September 30, 2021 (Successor) and December 31, 2020 (Successor) .
Emerging Growth Company Status	Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that the Company (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, the Company's unaudited consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.
New Accounting Pronouncements Not Yet Adopted	New Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) and also issued subsequent amendments to the initial guidance: ASU 2017-13, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2020-02, and ASU 2020-05 (collectively, “ASC 842”). ASC 842 outlines a comprehensive lease accounting model and supersedes the current lease guidance. The new guidance requires lessees to recognize lease liabilities and corresponding right-of-use assets for all leases with lease terms of greater than 12 months. It also changes the definition of a lease and expands the disclosure requirements of lease arrangements. ASC 842 is effective for private entities for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, inclusive of a one year deferral provided by ASU 2020-05. ASC 842 must be adopted using a modified retrospective method and early adoption is permitted. The Company is in the process of determining the impact of the adoption of ASC 842 on the Company’s consolidated financial statements and disclosures. However, given the Company’s current operating lease portfolio (see Note 16) the Company expects the recognition of the right-of-use assets and lease liabilities to have a material impact on the Company’s consolidated balance sheets. In June 2016, the FASB issued ASU 2016-13, Financial Instruments (Topic 326)-Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 requires an entity to utilize a new impairment model known as the current expected credit loss (“CECL”) model to estimate its lifetime “expected credit loss” and record an allowance that, when deducted from the amortized cost basis of the financial asset, presents the net amount expected to be collected on the financial asset. The CECL model is expected to result in more timely recognition of credit losses. ASU 2016-13 also requires new disclosures for financial assets measured at amortized cost, loans and available-for-sale debt securities. ASU 2016-13 is effective for private entities for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. ASU 2016-03 will apply as a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is adopted. The Company is in the process of evaluating the impact of the adoption of ASU 2016-13 on the Company’s consolidated financial statements and disclosures. In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. ASU 2019-12 is effective for private entities for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. Early adoption of the amendments is permitted, including adoption in any interim period for public business entities for periods for which financial statements have not yet been issued and all other entities for periods for which financial statements have not yet been made available for issuance. The Company is in the process of evaluating the impact of the adoption of ASU 2019-12 on the Company’s consolidated financial statements and disclosures. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”). This guidance provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions, subject to meeting certain criteria, that reference the London Interbank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. The amendments issued in March 2020 provide optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in ASU 2020-04 are effective for all entities as of March 12, 2020, through December 31, 2022. The Company is still evaluating the impact of adopting ASU 2020-04 on its consolidated financial statements and disclosures.

TPG Acquisition (Tables)

TPG Acquisition (Tables)	9 Months Ended
	Sep. 30, 2021
Schedule of Business Combination Consideration Transferred	Total consideration transferred consisted of the following: Cash consideration $ 670,941 Class A-1 units 345,978 Class A-2 units 35,845 Total consideration transferred $ 1,052,764
Schedule of Recognized Assets Acquired and Liabilities Assumed	The following table summarizes the fair values of assets acquired and liabilities assumed as of the dates of acquisition: Successor Predecessor Allocation of Purchase Price Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Cash $ 820 $ 326 $ 2,868 $ 1,574 $ 238 Patient accounts receivable 963 822 4,762 4,204 1,344 Property and equipment 89 26 783 616 234 Prepaid expenses and other current 86 26 313 103 68 Deposits 73 15 164 207 87 Intangible assets 1,260 469 4,321 3,613 2,080 Goodwill 22,198 8,664 63,485 33,323 14,099 Total assets acquired 25,489 10,348 76,696 43,640 18,150 Current liabilities 1,606 1,264 6,951 3,240 1,493 Total liabilities assumed 1,606 1,264 6,951 3,240 1,493 Fair value of net assets $ 23,883 $ 9,084 $ 69,745 $ 40,400 $ 16,657
Schedule of Acquired Intangible Assets	The following table summarizes the fair values of acquired intangible assets as of the date of the TPG Acquisition: Amount Useful Life Trade names – Corporate $ 235,500 22.5 years Trade names – Regional 22,900 5 years Non-competition agreements – Executives 77,500 4 years Non-competition agreements – Providers 8,400 5 years Total intangible assets $ 344,300
Schedule Of Unaudited Pro Forma Revenue and Net Loss	The Company’s unaudited pro forma revenue and net loss for the years ended December 31, 2020 and 2019 below have been prepared as if the TPG Acquisition occurred on January 1, 2019. Year ended Year ended Revenue $ 377,217 $ 212,518 Net loss $ ( 26,727 ) $ ( 52,463 )
T P G Acquisition
Schedule of Recognized Assets Acquired and Liabilities Assumed	The following table summarizes the fair values of assets acquired and liabilities assumed as of the date of acquisition: Allocation of Purchase Price Amount Cash $ 27,224 Patient accounts receivable 25,152 Property and equipment 34,813 Prepaid expenses and other current assets 9,590 Deposits 1,766 Intangible assets 344,300 Goodwill 926,658 Total assets acquired 1,369,503 Accounts payable 3,456 Accrued payroll expenses 25,739 Other accrued expenses 48,655 Current portion of contingent consideration 5,861 Other current liabilities 1,848 Long-term debt, net 135,006 Other noncurrent liabilities 9,617 Contingent consideration, net of current portion 4,048 Deferred tax liability, net 82,509 Total liabilities assumed 316,739 Fair value of net assets $ 1,052,764

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Summary Of Consideration Transferred	Total consideration transferred for these acquisitions consisted of the following: Successor Predecessor Total consideration transferred Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Cash consideration $ 21,108 $ 8,049 $ 62,420 $ 31,674 $ 12,369 Cash consideration to be paid — — 325 — — Contingent consideration, at initial 2,775 1,035 5,514 4,226 3,788 Class A-2 common units 1 — — 1,486 4,500 — Debt consideration — — — — 500 Total consideration transferred $ 23,883 $ 9,084 $ 69,745 $ 40,400 $ 16,657 (1) Excludes 511 Class A-2 common units related to the promissory note (see “Debt consideration”) issued during the Predecessor period that was subsequently converted to equity during the Successor period.
Schedule of Recognized Assets Acquired and Liabilities Assumed	The following table summarizes the fair values of assets acquired and liabilities assumed as of the dates of acquisition: Successor Predecessor Allocation of Purchase Price Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Cash $ 820 $ 326 $ 2,868 $ 1,574 $ 238 Patient accounts receivable 963 822 4,762 4,204 1,344 Property and equipment 89 26 783 616 234 Prepaid expenses and other current 86 26 313 103 68 Deposits 73 15 164 207 87 Intangible assets 1,260 469 4,321 3,613 2,080 Goodwill 22,198 8,664 63,485 33,323 14,099 Total assets acquired 25,489 10,348 76,696 43,640 18,150 Current liabilities 1,606 1,264 6,951 3,240 1,493 Total liabilities assumed 1,606 1,264 6,951 3,240 1,493 Fair value of net assets $ 23,883 $ 9,084 $ 69,745 $ 40,400 $ 16,657
Schedule of Fair Values of Acquired Intangible Assets	The following table summarizes the fair values of acquired intangible assets as of the dates of acquisition: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Regional trade names (1) $ 775 $ 266 $ 2,691 $ 2,304 $ 1,721 Non-Competition Agreements (2) 485 203 1,630 1,309 359 Total $ 1,260 $ 469 $ 4,321 $ 3,613 $ 2,080 (1) Useful lives for regional trade names are 5 years . (2) Useful lives for non-competition agreements are 5 years .
Schedule of Maximum Contingent Consideration Based on the Acquisition Agreements	The following table summarizes the maximum contingent consideration based on the acquisition agreements: Successor Predecessor Contingent consideration Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Maximum contingent consideration $ 3,400 $ 1,275 $ 6,750 $ 11,575 $ 4,336

Intangible Assets (Tables)

Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Intangible Assets	Intangible assets consists of the following: September 30, 2021 (Successor) Gross Accumulated Net Weighted Regional trade names $ 33,168 $ ( 7,933 ) $ 25,235 5.0 LifeStance trade names 235,500 ( 14,474 ) 221,026 22.5 Non-competition agreements 91,719 ( 29,998 ) 61,721 4.2 Total intangible assets $ 360,387 $ ( 52,405 ) $ 307,982 December 31, 2020 (Successor) Gross Accumulated Net Weighted Regional trade names $ 30,477 $ ( 3,178 ) $ 27,299 5.0 LifeStance trade names 235,500 ( 6,624 ) 228,876 22.5 Non-competition agreements 90,089 ( 13,468 ) 76,621 4.1 Total intangible assets $ 356,066 $ ( 23,270 ) $ 332,796
Summary of Intangible Assets Amortization Expense	Gross carrying amount is based on the fair value of the intangible assets determined at acquisitions. Total intangible asset amortization expense consists of the following: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Amortization expense $ 9,812 $ 9,260 $ 29,135 $ 13,929 $ 1,435

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consists of the following: Successor September 30, 2021 December 31, 2020 Leasehold improvements $ 75,625 $ 39,586 Computers and peripherals 13,252 5,749 Furniture, fixtures and equipment 16,490 8,726 Medical equipment 3,868 2,143 Construction in process 19,890 7,577 Total $ 129,125 $ 63,781 Less: Accumulated depreciation ( 14,076 ) ( 4,432 ) Total property and equipment, net $ 115,049 $ 59,349
Schedule of Depreciation Expense	Depreciation expense consists of the following: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Depreciation expense $ 3,965 $ 1,650 $ 9,644 $ 2,413 $ 1,900

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of the Significant Assumptions Used for the Fair Value Measurement of the Contingent Consideration Liability	The following is the summary of the significant assumptions used for the fair value measurement of the contingent consideration liability as of September 30, 2021 (Successor) and December 31, 2020 (Successor). Valuation Technique Range of Significant Assumptions Successor September 30, 2021 Probability-weighted analysis Probability 25 % - 100 % based earn-outs (1) Discount rate 8.65 % - 8.68 % (1) During the second quarter of 2021, all contingent consideration liabilities previously estimated using a Monte Carlo Simulation EBITDA based earn-out technique transitioned, as deemed appropriate due to the remaining timing of the contracts and materiality of the underlying balances, to a probability-weighted analysis based on projected outcomes. Valuation Technique Range of Significant Assumptions Successor December 31, 2020 Monte Carlo Simulation Expected EBITDA Acquisition specific EBITDA based earn-outs Discount rate 16.15 % - 19.65 % Counter-party risk premium 8.46 % - 8.77 % Volatility 50 % Probability-weighted analysis Probability 25 % - 100 % FTE based earn-outs Discount rate 8.65 % - 8.68 %
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following table presents information about the Company’s liabilities that are measured at fair value on a recurring basis using the above input categories: September 30, 2021 (Successor) Level 1 Level 2 Level 3 Total Financial Instrument Contingent consideration liability $ — $ — $ 17,129 $ 17,129 December 31, 2020 (Successor) Level 1 Level 2 Level 3 Total Financial Instrument Contingent consideration liability $ — $ — $ 16,414 $ 16,414

GOODWILL (Tables)

GOODWILL (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Goodwill	Goodwill consists of the following: Amount Beginning balance as of April 13, 2020 (Successor) $ — TPG Acquisition (Note 3) 926,658 Measurement period adjustment (Note 3) 2,977 Business acquisitions 169,024 Ending balance as of December 31, 2020 (Successor) $ 1,098,659 Business acquisitions (Note 4) 63,485 Measurement period adjustments ( 2,133 ) Ending balance as of September 30, 2021 (Successor) $ 1,160,011

Long- Term Debt (Tables)

Long- Term Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Summary of Long-term Debt Instruments	Long-term debt consists of the following: Successor September 30, 2021 December 31, 2020 Term loans $ 70,902 $ 283,950 Delayed Draw loans 90,659 89,870 Total long-term debt 161,561 373,820 Less: Current portion of long-term debt ( 1,323 ) ( 3,738 ) Less: Unamortized debt issue costs ( 2,791 ) ( 7,548 ) Total Long-Term Debt, Net of Current Portion $ 157,447 $ 362,534
Summary of Interest Expense	Interest expense, including prepayment charge, consists of the following: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Interest expense $ 3,503 $ 6,421 $ 35,309 $ 11,983 $ 3,020
Summary of Maturities of Long-term Debt	Future principal payments on long-term debt are as follows: Amount Remainder of 2021 $ 331 2022 1,323 2023 1,323 2024 1,323 2025 1,323 Thereafter 155,938 Total $ 161,561

TOTAL REVENUES (Tables)

TOTAL REVENUES (Tables)	9 Months Ended
	Sep. 30, 2021
Disaggregation Of Revenue [Abstract]
Schedule of revenue from patients and third - party payors	The payor mix of fee-for-service revenue from patients and third-party payors consists of the following: Successor Three Months Ended Three Months Ended Nine Months Ended Amount % of Total Revenue Amount % of Total Revenue Amount % of Total Revenue Commercial $ 158,035 91 % $ 90,810 89 % $ 433,684 91 % Government 8,731 5 % 4,782 5 % 20,942 4 % Self-pay 5,948 3 % 4,416 4 % 19,230 4 % Total patient service revenue 172,714 99 % 100,008 98 % 473,856 99 % Nonpatient service revenue 1,121 1 % 1,974 2 % 3,660 1 % Total $ 173,835 100 % $ 101,982 100 % $ 477,516 100 % Successor Predecessor April 13 to January 1 to May 14, 2020 Amount % of Total Revenue Amount % of Total Revenue Commercial $ 129,983 88 % $ 98,146 88 % Government 7,468 5 % 5,411 5 % Self-pay 6,703 5 % 4,821 4 % Total patient service revenue 144,154 98 % 108,378 97 % Nonpatient service revenue 3,281 2 % 3,283 3 % Total $ 147,435 100 % $ 111,661 100 %
Schedule of percentage of revenue from insurance companies	Among the commercial payors, five insurance companies comprise the following percentage of revenue. Three payors individually exceed 10 % of the Company’s revenue for the three months ended September 30, 2021 (Successor), the three months ended September 30, 2020 (Successor), the nine months ended September 30, 2021 (Successor), the period from April 13, 2020 to September 30, 2020 (Successor) , and the period from January 1, 2020 to May 14, 2020 (Predecessor). Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Top five commercial payors 63 % 69 % 63 % 67 % 67 % Top one payor 19 % 23 % 19 % 23 % 23 % Top two payor 18 % 18 % 17 % 19 % 19 % Top three payor 12 % 13 % 13 % 13 % 11 %

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Schedule of Income Tax Expense Benefit	The benefit for income taxes is as follows: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Benefit from income taxes $ 8,751 $ 1,074 $ 15,300 $ 2,444 $ 2,319
Schedule of Effective Tax Rates	The effective tax rates are as follows: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Effective tax rate 6.8 % 24.6 % 7.1 % 24.2 % 8.5 %

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Units (Tables)	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
Summary of Preferred Units Prior to the TPG Acquisition	The table below includes the number of authorized units and issued units, as well as the issuance price, liquidation preference and initial carrying amount of the Preferred Units immediately prior to the TPG Acquisition, which occurred on May 14, 2020. Year of Authorized Issued Units Issuance Price Liquidation Initial Carrying Unit Series Series A-1 2017 110,898 87,000 $ 1.00 $ 106,978 $ 87,000 2018 110,898 22,838 1.00 26,568 22,838 109,838 $ 133,546 $ 109,838 Series A 2017 23,600 11,741 $ 1.00 $ 14,504 $ 11,741 2018 23,600 1,500 1.50 2,536 2,250 2019 23,600 2,885 2.00 6,276 5,770 16,126 $ 23,316 $ 19,761

Stock And Unit-Based Compensa_2

Stock And Unit-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Summary of Restricted Stock Awards (RSA) Activity	The following is a summary of restricted stock transactions as of and for the three and nine months ended September 30, 2021 (Successor): Unvested Shares Weighted-Average Grant Date Unvested, June 30, 2021 (Successor) 30,766 $ 11.98 Converted — — Granted — — Vested ( 17 ) 12.01 Unvested, September 30, 2021 (Successor) 30,749 $ 11.98 Unvested Shares Weighted-Average Grant Date Unvested, June 9, 2021 (Successor) — $ — Converted 30,766 11.98 Granted — — Vested ( 17 ) 12.01 Unvested, September 30, 2021 (Successor) 30,749 $ 11.98
Summary of Restricted Stock Unit (RSU) Activity	The following is a summary of RSU transactions as of and for the three and nine months ended September 30, 2021 (Successor): Unvested Shares Weighted-Average Grant Date Outstanding, June 30, 2021 (Successor) 6,128 $ 18.00 Converted — — Granted 80 12.87 Vested — — Outstanding, September 30, 2021 (Successor) 6,208 $ 17.93 Unvested Shares Weighted-Average Grant Date Outstanding, June 9, 2021 (Successor) — $ — Converted — — Granted 6,208 17.93 Vested — — Outstanding, September 30, 2021 (Successor) 6,208 $ 17.93
Summary of Stock and Unit Based Compensation Award Valuation Assumptions	Accordingly, the Company determined the fair value of each award on the date of grant using a Monte Carlo simulation model with the following assumptions used for the grants issued for the nine months ended September 30, 2021 (Successor), for the three months ended September 30, 2020 (Successor) and for the period from April 13, 2020 to September 30, 2020 (Successor): Successor Nine Months Ended Three Months Ended September 30, 2020 April 13 to Risk-free rate 0.14 % 0.20 % 0.20 % Volatility 80.00 % 40.00 % 40.00 % Time to liquidity event (years) 2.00 3.00 3.00 Discount for lack of marketability (DLOM) — 20.00 % 20.00 %
Summary of Class B Profits Interests Units	The following is a summary of Class B Profits Interests Units for the nine months ended September 30, 2021 (Successor), for the three months ended September 30, 2020 (Successor) and for the period from April 13, 2020 to September 30, 2020 (Successor): Class B Profits Weighted- Outstanding, December 31, 2020 143,343 $ 0.13 Granted 9,522 0.16 Forfeited ( 245 ) 0.13 Converted ( 152,620 ) 0.13 Outstanding, September 30, 2021 (Successor) — $ — Class B Profits Weighted- Outstanding, June 30, 2020 134,855 $ 0.13 Granted 627 0.13 Outstanding, September 30, 2020 (Successor) 135,482 $ 0.13 Class B Profits Weighted- Outstanding, April 13, 2020 — $ — Granted 135,482 0.13 Outstanding, September 30, 2020 (Successor) 135,482 $ 0.13
Summary of Unit Based Compensation Expense	The Company recognized unit-based compensation expense related to the Class B Profits Interests within general and administrative expenses in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss) as follows: Successor Three Months Ended Nine Months Ended April 13 to Unit-based compensation expense $ 573 $ 1,135 $ 865

Stockholders' Equity Members'_2

Stockholders' Equity Members' Deficit (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Schedule of Common Stock	The Company’s common stock/units consisted of the following common units and common stock as of the periods ended September 30, 2021 (Successor) and December 31, 2020 (Successor): Redeemable Class A-1 Units Class A-2 Units Class B Units Common Stock Total Balance as of April 13, — — — — — — Issued 35,000 959,563 49,946 — — 1,044,509 Balance as of 35,000 959,563 49,946 — — 1,044,509 Issued — — 1,687 — — 1,687 Vested Class B Profits — — — 17,920 — 17,920 Conversion of pre-IPO ( 35,000 ) ( 959,563 ) ( 51,633 ) ( 17,920 ) 340,849 ( 723,267 ) Initial Public Offering — — — — 32,800 32,800 Endowment to the — — — — 500 500 Balance as of September — — — — 374,149 374,149

Related Party Transactions (Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Schedule Of Related-party Rent Expense	Total related-party rent expense included in center costs in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss) amounted to: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Rent expense $ 809 $ 262 $ 2,006 $ 369 $ 388
Schedule Of Future Minimum Rental Payments For Operating Leases Table	A summary of non-cancelable future minimum operating lease payments under these leases as of September 30, 2021 (Successor) is as follows: Amount Remainder of 2021 $ 761 2022 2,973 2023 2,688 2024 2,415 2025 2,333 Thereafter 1,501 Total $ 12,671
Schedule of Related Party Management Fees	Total related-party management fees amounted to: Successor Predecessor Three Months Ended Nine Months Ended April 13 to January 1 to Management fees $ 44 $ 1,445 $ 60 $ 14

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Business Acquisition, Contingent Consideration [Line Items]
Schedule of Maximum Contingent Consideration Based on the Acquisition Agreements	The following table summarizes the maximum contingent consideration based on the acquisition agreements: Successor Predecessor Contingent consideration Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Maximum contingent consideration $ 3,400 $ 1,275 $ 6,750 $ 11,575 $ 4,336
Schedule Of Related-party Rent Expense	Total related-party rent expense included in center costs in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss) amounted to: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Rent expense $ 809 $ 262 $ 2,006 $ 369 $ 388
Contingent Consideration [Member]
Business Acquisition, Contingent Consideration [Line Items]
Schedule of Maximum Contingent Consideration Based on the Acquisition Agreements	The following table presents changes to the Company’s contingent consideration balance: Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Beginning balance $ 14,123 $ 10,951 $ 16,414 $ — $ 25,536 Additions related to TPG Acquisition — — — 9,909 — Additions related to acquisitions 2,775 1,035 5,514 4,226 3,788 Payments of contingent consideration ( 675 ) ( 100 ) ( 6,262 ) ( 2,300 ) ( 19,093 ) Loss (gain) on remeasurement 906 ( 89 ) 1,463 ( 38 ) ( 322 ) Ending balance $ 17,129 $ 11,797 $ 17,129 $ 11,797 $ 9,909
Schedule Of Related-party Rent Expense	Total third-party rent expense amounted to as follows in the unaudited consolidated statements of income/(loss) and comprehensive income/(loss): Successor Predecessor Three Months Ended Three Months Ended Nine Months Ended April 13 to January 1 to Center costs $ 8,302 $ 4,484 $ 21,878 $ 6,779 $ 4,082 General and administrative expenses 127 122 655 183 128 Total rent expense $ 8,429 $ 4,606 $ 22,533 $ 6,962 $ 4,210
Summary of Future Minimum Lease Payments	A summary of non-cancellable future minimum third-party operating lease payments under these leases as of September 30, 2021 (Successor) is as follows: Amount Remainder of 2021 $ 6,391 2022 26,183 2023 25,093 2024 21,140 2025 17,072 Thereafter 33,724 Total $ 129,603

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss Per Share	The following table presents the calculation of basic and diluted net income/(loss) per share (“EPS”) for the Company’s common shares (on an as-converted basis): Successor Three Months Ended Three Months Ended Nine Months Ended April 13 to Net loss available to common $ ( 120,452 ) $ ( 3,294 ) $ ( 235,917 ) $ ( 7,636 ) Weighted-average shares used to compute 343,394 302,657 321,283 300,799 Net loss per share, basic and diluted $ ( 0.35 ) $ ( 0.01 ) $ ( 0.73 ) $ ( 0.03 )

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 25, 2021	Jun. 14, 2021	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Organisation incorporated date					Jan. 28, 2021
Issuance of common , Shares					1,687,000	1,044,509,000
Proceeds from initial public offering			$ 0	$ 0	$ 548,905
Reclassification of redeemable investor units					71,648
Reclassification of common units to additional paid in capital					1,008,688
Reclassification of Common Stock					$ 3,408
Life Stance Health Foundation [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common , Shares					500,000
Cash payment for restructuring					$ 1,000
Aggregate cost					$ 10,000
LifeStance TopCo
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of units converted					1,046,196,000
LifeStance [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from initial public offering		$ 548,905
Payments for underwriting expense		32,472
Deferred offering costs		$ 9,023
Conversion of common units into common stock upon closing of initial public offering, Shares					310,083,000
Common Stock Subject To Service-Based Vesting [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Conversion of common units into common stock upon closing of initial public offering, Shares					30,766,000
Common Stock [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Conversion of common units into common stock upon closing of initial public offering, Shares					295,663,000
Class B Profits Interests Units [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of units converted					152,620
Selling Shareholders [Member] | Common Stock [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common , Shares		7,200,000
Shares offering, price per share		$ 18
IPO
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares offering, price per share					$ 18
IPO | LifeStance [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common , Shares		32,800,000
IPO | Common Stock [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common , Shares					32,800,000
Over-Allotment Option
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common , Shares	6,000,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	Sep. 30, 2021
Accounting Policies [Abstract]
Acquisition of Non Medical Assets	100.00%

TPG Acquisition - Additional In

TPG Acquisition - Additional Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	May 14, 2020	Apr. 13, 2020
Business Acquisition [Line Items]
Common Stock, Shares, Issued	374,149	0
Class of units	$ 381,823
Common Stock, par value	$ 0.01	$ 0.01
Cash consideration	$ 670,941
Escrow deposit	4,500
Fair value of net assets acquired			$ 126,106
Goodwill	1,160,011	$ 1,098,659	$ 926,658	$ 0
Additional Cash Payment Related to a Working Capital Adjustment	$ (2,133)	2,977
Class A-1 Units
Business Acquisition [Line Items]
Common Stock, Shares, Issued	345,978
Class A-2 Common Units [Member]
Business Acquisition [Line Items]
Common Stock, Shares, Issued	35,845
Common Stock, par value	$ 1
T P G Acquisition
Business Acquisition [Line Items]
Date of acquisition agreement	Apr. 14, 2020
Business acquisition, equity percentage interests acquired	100.00%
Total consideration transferred	$ 1,052,764
Cash consideration	670,941
Goodwill	926,658
Additional Cash Payment Related to a Working Capital Adjustment		$ 2,977
Transaction costs	$ 32,942
T P G Acquisition | Class A-1 Units
Business Acquisition [Line Items]
Common Stock, Shares, Issued	979,563
Class of units	$ 345,978
T P G Acquisition | Class A-2 Common Units [Member]
Business Acquisition [Line Items]
Common Stock, Shares, Issued	35,845
Class of units	$ 35,845

TPG Acquisition - Summary of Bu

TPG Acquisition - Summary of Business Consideration Trnsferred (Detaills) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Business Acquisition [Line Items]
Cash consideration	$ 670,941
Class of units	381,823
T P G Acquisition
Business Acquisition [Line Items]
Cash consideration	670,941
Total consideration transferred	1,052,764
T P G Acquisition | Class A-1 Units
Business Acquisition [Line Items]
Class of units	345,978
T P G Acquisition | Class A-2 Common Units [Member]
Business Acquisition [Line Items]
Class of units	$ 35,845

TPG Acquisition - Summary of Re

TPG Acquisition - Summary of Recognized Asset acquired and Liability Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	May 14, 2020	Apr. 13, 2020
Business Acquisition [Line Items]
Goodwill	$ 1,160,011	$ 1,098,659	$ 926,658	$ 0
Current portion of contingent consideration	17,129	16,414
Current portion of contingent consideration	14,012	$ 10,563
T P G Acquisition
Business Acquisition [Line Items]
Cash	27,224
Patient accounts receivable	25,152
Property and equipment	34,813
Prepaid expenses and other current assets	9,590
Deposits	1,766
Intangible assets	344,300
Goodwill	926,658
Total assets acquired	1,369,503
Accounts payable	3,456
Accrued payroll expenses	25,739
Other accrued expenses	48,655
Current portion of contingent consideration	5,861
Other current liabilities	1,848
Long-term debt, net	135,006
Other noncurrent liabilities	9,617
Current portion of contingent consideration	4,048
Deferred tax liability, net	82,509
Total liabilities assumed	316,739
Fair value of net assets	$ 1,052,764

TPG Acquisition - Summary of Fa

TPG Acquisition - Summary of Fair value of Acquired Intangible Assets (Details) - T P G Acquisition $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Business Acquisition [Line Items]
Intangible assets	$ 344,300
Trade Name Corporate
Business Acquisition [Line Items]
Intangible assets	$ 235,500
Intangible assets useful life	22 years 6 months
Trade Name Regional
Business Acquisition [Line Items]
Intangible assets	$ 22,900
Intangible assets useful life	5 years
Non Competition Agreements Executives
Business Acquisition [Line Items]
Intangible assets	$ 77,500
Intangible assets useful life	4 years
Non Competition Agreements Providers
Business Acquisition [Line Items]
Intangible assets	$ 8,400
Intangible assets useful life	5 years

TPG Acquisition - Schedule of U

TPG Acquisition - Schedule of Unaudited Pro Forma Revenue and Net Loss (Details) - T P G Acquisition [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Revenue	$ 377,217	$ 212,518
Net loss	$ (26,727)	$ (52,463)

Acquisitions - Additional Infor

Acquisitions - Additional Information (Details) - Facility	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Business Combinations [Abstract]
Acquisitions of outpatient mental health practices	6	2	6	6	17

Acquisitions - Summary of Consi

Acquisitions - Summary of Consideration Transferred (Details) - USD ($) $ in Thousands		3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Business Acquisition [Line Items]
Class of units						$ 381,823
Outpatient Mental Health Practices
Business Acquisition [Line Items]
Cash consideration		$ 21,108	$ 8,049	$ 12,369	$ 31,674	62,420
Contingent consideration, at initial fair value		0	0	0	0	325
Debt consideration		0	0	500	0	0
Total consideration transferred		23,883	9,084	16,657	40,400	69,745
Debt [Member] | Outpatient Mental Health Practices
Business Acquisition [Line Items]
Debt consideration	[1]	0	0	0	4,500	1,486
Class A-2 Common Units [Member] | Outpatient Mental Health Practices
Business Acquisition [Line Items]
Class of units		$ 2,775	$ 1,035	$ 3,788	$ 4,226	$ 5,514
[1]	Excludes 511 Class A-2 common units related to the promissory note (see “Debt consideration”) issued during the Predecessor period that was subsequently converted to equity during the Successor period.

Acquisitions - Schedule of Fair

Acquisitions - Schedule of Fair Value Assets Acquired And Liabilities Assumed (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Business Combinations [Abstract]
Cash	$ 820	$ 326	$ 238	$ 1,574	$ 2,868
Patient accounts receivable	963	822	1,344	4,204	4,762
Property and equipment	89	26	234	616	783
Prepaid expenses and other current assets	86	26	68	103	313
Deposits	73	15	87	207	164
Intangible assets	1,260	469	2,080	3,613	4,321
Goodwill	22,198	8,664	14,099	33,323	63,485
Total assets acquired	25,489	10,348	18,150	43,640	76,696
Current liabilities	1,606	1,264	1,493	3,240	6,951
Total liabilities assumed	1,606	1,264	1,493	3,240	6,951
Fair value of net assets	$ 23,883	$ 9,084	$ 16,657	$ 40,400	$ 69,745

Acquisitions - Schedule of Fa_2

Acquisitions - Schedule of Fair Values of Acquired Intangible Assets (Details) - USD ($) $ in Thousands		3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Business Acquisition [Line Items]
Acquired intangible assets, Fair value		$ 1,260	$ 469	$ 2,080	$ 3,613	$ 4,321
Regional Trade Names [Member]
Business Acquisition [Line Items]
Acquired intangible assets, Fair value	[1]	775	266	1,721	2,304	2,691
Non-Competition Agreements [Member]
Business Acquisition [Line Items]
Acquired intangible assets, Fair value	[2]	$ 485	$ 203	$ 359	$ 1,309	$ 1,630
[1]	Useful lives for regional trade names are 5 years .
[2]	Useful lives for non-competition agreements are 5 years .

Acquisitions - Schedule of Fa_3

Acquisitions - Schedule of Fair Values of Acquired Intangible Assets (Parenthetical) (Details)	9 Months Ended
	Sep. 30, 2021
Regional Trade Names [Member]
Business Acquisition [Line Items]
Useful lives for acquired intangible assets	5 years
Non-Competition Agreements [Member]
Business Acquisition [Line Items]
Useful lives for acquired intangible assets	5 years

Acquisitions - Schedule of Maxi

Acquisitions - Schedule of Maximum Contingent Consideration Based on the Acquisition Agreements (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Contingent Consideration [Member]
Business Acquisition [Line Items]
Maximum contingent consideration based on acquisition agreements	$ 3,400	$ 1,275	$ 4,336	$ 11,575	$ 6,750

Intangible Assets - Summary of

Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 360,387	$ 356,066
Accumulated Amortization	(52,405)	(23,270)
Net Carrying Amount	307,982	332,796
Regional Trade Names [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	33,168	30,477
Accumulated Amortization	(7,933)	(3,178)
Net Carrying Amount	$ 25,235	$ 27,299
Intangible assets useful life	5 years	5 years
Life Stance Trade Names [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 235,500	$ 235,500
Accumulated Amortization	(14,474)	(6,624)
Net Carrying Amount	$ 221,026	$ 228,876
Intangible assets useful life	22 years 6 months	22 years 6 months
Non-Competition Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 91,719	$ 90,089
Accumulated Amortization	(29,998)	(13,468)
Net Carrying Amount	$ 61,721	$ 76,621
Intangible assets useful life	4 years 2 months 12 days	4 years 1 month 6 days

Intangible Assets - Summary o_2

Intangible Assets - Summary of Intangible Asset Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Amortization expense	$ 9,812	$ 9,260	$ 1,435	$ 13,929	$ 29,135

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total	$ 129,125	$ 63,781
Less: Accumulated depreciation	(14,076)	(4,432)
Total property and equipment, net	115,049	59,349
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Total	75,625	39,586
Computers and Peripherals [Member]
Property Plant And Equipment [Line Items]
Total	13,252	5,749
Furniture, Fixtures and Equipment [Member]
Property Plant And Equipment [Line Items]
Total	16,490	8,726
Medical Equipment [Member]
Property Plant And Equipment [Line Items]
Total	3,868	2,143
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Total	$ 19,890	$ 7,577

Property and Equipment - Sche_2

Property and Equipment - Schedule of Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Depreciation expense	$ 3,965	$ 1,650	$ 1,900	$ 2,413	$ 9,644

FAIR VALUE MEASUREMENTS - Summa

FAIR VALUE MEASUREMENTS - Summary of the Significant Assumptions Used for the Fair Value Measurement of the Contingent Consideration Liability (Details)	Sep. 30, 2021	[1]	Dec. 31, 2020
E B I T D A Based Earn Outs | Volatility [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input			0.50
Minimum | E B I T D A Based Earn Outs
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input			0.1615
Minimum | E B I T D A Based Earn Outs | Counter-Party Risk Premium [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input			0.0846
Minimum | Probability Weighted Analysis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	0.25		25
Minimum | F T E Based Earn Outs
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	0.0865		8.65
Maximum | E B I T D A Based Earn Outs
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input			0.1965
Maximum | E B I T D A Based Earn Outs | Counter-Party Risk Premium [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input			0.0877
Maximum | Probability Weighted Analysis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	1		100
Maximum | F T E Based Earn Outs
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	0.0868		8.68
[1]	During the second quarter of 2021, all contingent consideration liabilities previously estimated using a Monte Carlo Simulation EBITDA based earn-out technique transitioned, as deemed appropriate due to the remaining timing of the contracts and materiality of the underlying balances, to a probability-weighted analysis based on projected outcomes.

FAIR VALUE MEASUREMENTS - Sum_2

FAIR VALUE MEASUREMENTS - Summary of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration liability	$ 17,129	$ 16,414
Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration liability	0	0
Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration liability	0	0
Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration liability	$ 17,129	$ 16,414

FAIR VALUE MEASUREMENTS - Addit

FAIR VALUE MEASUREMENTS - Additional Information (Details) $ in Thousands	Sep. 30, 2021USD ($)
Fair Value Disclosures [Abstract]
Materail assets or liabilities measured at fair value on a recurring basis	$ 0

GOODWILL - Schedule of Goodwill

GOODWILL - Schedule of Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Goodwill [Line Items]
Beginning balance	$ 1,098,659	$ 0
Business acquisitions	63,485	169,024
Measurement period adjustment	(2,133)	2,977
Ending balance	1,160,011	1,098,659
T P G Acquisition
Goodwill [Line Items]
Business acquisitions		926,658
Measurement period adjustment		$ 2,977
Ending balance	$ 926,658

Long- Term Debt - Summary of Lo

Long- Term Debt - Summary of Long-term Debt Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	May 14, 2020
Debt Instrument [Line Items]
Term loans	$ 157,447	$ 362,534
Less: Current portion of long-term debt	(1,323)	(3,738)
Less: Unamortized debt issue costs	(2,791)	(7,548)
Total	161,561	373,820
Term Loans
Debt Instrument [Line Items]
Total	70,902	283,950	$ 210,000
Delayed Drawn Loans
Debt Instrument [Line Items]
Total	$ 90,659	$ 89,870	$ 50,000

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail) - USD ($) $ in Thousands	Apr. 30, 2021	Nov. 04, 2020	May 14, 2020	Mar. 31, 2021	Sep. 30, 2021	Jun. 15, 2021	Feb. 28, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term Debt, Fair Value					$ 187,780			$ 458,685
Voluntary Prepayment of Borrowings Outstanding						$ 294,000
Extinguishment of Debt, Amount				$ 14,444
Unamortized Debt Issuance Expense			$ 2,689
Long-term debt, net					161,561			373,820
Long-term Debt, Maturities, Repayment Terms			May 14, 2026
May 2020 Credit Agreement [Member]
Debt Instrument [Line Items]
Aggregate loan commitment amount	$ 70,000	$ 115,000
Increase in term loan		75,000
Revolving Credit Facility [Member] | May 2020 Credit Agreement [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 20,000
Unused revolving loan commitment fee percentage					0.005
Revolving loan outstanding amount					$ 0
Revolving loan,expiration date					May 14, 2025
Term Loans
Debt Instrument [Line Items]
Long-term debt, net			$ 210,000		$ 70,902			283,950
Term Loans | May 2020 Credit Agreement [Member]
Debt Instrument [Line Items]
Increase in term loan	20,000
Delayed Drawn Loans
Debt Instrument [Line Items]
Long-term debt, net			$ 50,000		$ 90,659			$ 89,870
Delayed Drawn Loans | May 2020 Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term debt, net		$ 40,000
Aggregate loan commitment amount	$ 50,000						$ 50,000
London Interbank Offered Rate (LIBOR) [Member] | Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			3.25%
London Interbank Offered Rate (LIBOR) [Member] | Minimum | Revolving Credit Facility [Member] | May 2020 Credit Agreement [Member]
Debt Instrument [Line Items]
Interest Rate					4.50%
London Interbank Offered Rate (LIBOR) [Member] | Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			3.75%
London Interbank Offered Rate (LIBOR) [Member] | Maximum | Revolving Credit Facility [Member] | May 2020 Credit Agreement [Member]
Debt Instrument [Line Items]
Interest Rate					4.75%

Summary of Interest Expense (De

Summary of Interest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Debt Disclosure [Abstract]
Interest expense	$ 3,503	$ 6,421	$ 3,020	$ 11,983	$ 35,309

Future Principal Payments on Lo

Future Principal Payments on Long Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Remainder of 2021	$ 331
2022	1,323
2023	1,323
2024	1,323
2025	1,323
Thereafter	155,938
Total	$ 161,561	$ 373,820

TOTAL REVENUES - Schedule of Re

TOTAL REVENUES - Schedule of Revenue From Patients And Third - Party Payors (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Amount	$ 173,835	$ 101,982	$ 111,661	$ 147,435	$ 477,516
% of Total Revenue	100.00%	100.00%	100.00%	100.00%	100.00%
Commercial
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Amount	$ 158,035	$ 90,810	$ 98,146	$ 129,983	$ 433,684
% of Total Revenue	91.00%	89.00%	88.00%	88.00%	91.00%
Government
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Amount	$ 8,731	$ 4,782	$ 5,411	$ 7,468	$ 20,942
% of Total Revenue	5.00%	5.00%	5.00%	5.00%	4.00%
Self-pay
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Amount	$ 5,948	$ 4,416	$ 4,821	$ 6,703	$ 19,230
% of Total Revenue	3.00%	4.00%	4.00%	5.00%	4.00%
Total patient service revenue
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Amount	$ 172,714	$ 100,008	$ 108,378	$ 144,154	$ 473,856
% of Total Revenue	99.00%	98.00%	97.00%	98.00%	99.00%
Nonpatient service revenue
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Amount	$ 1,121	$ 1,974	$ 3,283	$ 3,281	$ 3,660
% of Total Revenue	1.00%	2.00%	3.00%	2.00%	1.00%

TOTAL REVENUES - Additional Inf

TOTAL REVENUES - Additional Information (Details)	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020
Three Payor | Minimum
Health Care Organization Receivable And Revenue Disclosures [Line Items]
Percentage of revenue	10.00%	10.00%	10.00%

TOTAL REVENUES - Schedule of Pe

TOTAL REVENUES - Schedule of Percentage Of Revenue From Insurance Companies (Details)	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Health Care Organization Receivable And Revenue Disclosures [Line Items]
% of Total Revenue	100.00%	100.00%	100.00%	100.00%	100.00%
Top five commercial payors
Health Care Organization Receivable And Revenue Disclosures [Line Items]
% of Total Revenue	63.00%	69.00%	67.00%	67.00%	63.00%
Top one payor
Health Care Organization Receivable And Revenue Disclosures [Line Items]
% of Total Revenue	19.00%	23.00%	23.00%	23.00%	19.00%
Top two payor
Health Care Organization Receivable And Revenue Disclosures [Line Items]
% of Total Revenue	18.00%	18.00%	19.00%	19.00%	17.00%
Top three payor
Health Care Organization Receivable And Revenue Disclosures [Line Items]
% of Total Revenue	12.00%	13.00%	11.00%	13.00%	13.00%

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Income Statement [Abstract]
Benefit from income taxes	$ 8,751	$ 1,074	$ 2,319	$ 2,444	$ 15,300

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Tax Rates (Details)	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Income Statement [Abstract]
Effective tax rate	6.80%	24.60%	8.50%	24.20%	7.10%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory tax rate	21.00%
Effective tax rate due to its valuation allowance	$ 0	$ 0

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Units - Additional Information (Details)	Sep. 30, 2021
T P G Acquisition
Business acquisition, equity percentage interests acquired	100.00%

Redeemable Convertible Prefer_4

Redeemable Convertible Preferred Units - Redeemable Convertible Preferred Units (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares
Series A1 Preferred Stock
Issued Units | shares	109,838
Liquidation Preference	$ 133,546
Initial Carrying Amount	$ 109,838
Series A1 Preferred Stock | 2017
Year of Issuance	2017
Authorized Units | shares	110,898
Issued Units | shares	87,000
Issuance Price per Unit | $ / shares	$ 1
Liquidation Preference	$ 106,978
Initial Carrying Amount	$ 87,000
Series A1 Preferred Stock | 2018
Year of Issuance	2018
Authorized Units | shares	110,898
Issued Units | shares	22,838
Issuance Price per Unit | $ / shares	$ 1
Liquidation Preference	$ 26,568
Initial Carrying Amount	$ 22,838
Series A Preferred Stock
Issued Units | shares	16,126
Liquidation Preference	$ 23,316
Initial Carrying Amount	$ 19,761
Series A Preferred Stock | 2017
Year of Issuance	2017
Authorized Units | shares	23,600
Issued Units | shares	11,741
Issuance Price per Unit | $ / shares	$ 1
Liquidation Preference	$ 14,504
Initial Carrying Amount	$ 11,741
Series A Preferred Stock | 2018
Year of Issuance	2018
Authorized Units | shares	23,600
Issued Units | shares	1,500
Issuance Price per Unit | $ / shares	$ 1.50
Liquidation Preference	$ 2,536
Initial Carrying Amount	$ 2,250
Series A Preferred Stock | 2019
Year of Issuance	2019
Authorized Units | shares	23,600
Issued Units | shares	2,885
Issuance Price per Unit | $ / shares	$ 2
Liquidation Preference	$ 6,276
Initial Carrying Amount	$ 5,770

Stock And Unit-Based Compensa_3

Stock And Unit-Based Compensation - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended	4 Months Ended		9 Months Ended
	Aug. 31, 2021shares	Sep. 30, 2021USD ($)shares	Sep. 30, 2021USD ($)shares	May 14, 2020USD ($)	Sep. 30, 2021USD ($)shares	Jun. 09, 2021shares	Dec. 31, 2020shares	Sep. 30, 2020shares	Jun. 30, 2020shares	Apr. 13, 2020shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensattion expense | $		$ 331,241	$ 331,241		$ 331,241
Unrecognized compensattion expense, weighted-average period					1 year 10 months 24 days
Restricted Stock Units RSU [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Payment Arrangement, Expense | $		120,689			$ 149,674
Restricted Stock Award
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Payment Arrangement, Expense | $		$ 120,689			$ 149,674
Class B Profits Interests Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Company's common stock						152,865,000
Class B Profit Interests Units outstanding		0	0		0		143,343,000	135,482,000	134,855,000	0
Class B Profits Interests Units [Member] | Restricted Stock Units RSU [Member] | IPO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock compensation expense | $					$ 149,674
Maximum | Class B Profits Interests Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Company's common stock						179,190,000
2021 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Company's common stock		47,037,000	47,037,000		47,037,000
Share-based compensation arrangement by share-based payment award, description			The share pool will automatically increase on January 1 of each year beginning in 2022 and continuing through and including 2031 by the lesser of (i) five percent of the number of shares of the Company’s common stock outstanding as of the close of business on the immediately preceding December 31 and (ii) the number of shares determined by the Board on or prior to such date for such year.
2021 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, description	January 1 of each year beginning in 2022 and continuing through and including 2031, equal to the lesser of (i) one percent of the number of shares of the Company’s common stock outstanding as of the close of business on the immediately preceding December 31 and (ii) the number of shares determined by the Board on or prior to such date for such year, up to a maximum of 42,500 shares of the Company’s common stock in the aggregate.
Exercise o stock options	6,817,000
Percentage of Purchase Price	85
2021 Employee Stock Purchase Plan [Member] | Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Issued During Period, Shares, Employee Stock Purchase Plans					0
2021 Employee Stock Purchase Plan [Member] | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Company's common stock	42,500,000
Percentage of deduction on pay roll.	15
Class C Units and Class A Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Payment Arrangement, Expense | $				$ 0

Stock And Unit-Based Compensa_4

Stock And Unit-Based Compensation - Summary of Restricted Stock Awards (RSA) Activity (Details) - Restricted Stock Award - $ / shares shares in Thousands	3 Months Ended	4 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding	30,766	0
Conversion	0	30,766
Granted	0	0
Vested	(17)	(17)
Outstanding	30,749	30,749
Outstanding	$ 11.98	$ 0
Conversion	0	11.98
Granted	0	0
Vested	12.01	12.01
Outstanding	$ 11.98	$ 11.98

Stock And Unit-Based Compensa_5

Stock And Unit-Based Compensation - Summary of Restricted Stock Unit (RSU) Activity (Details) - Restricted Stock Unit - $ / shares shares in Thousands	3 Months Ended	4 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding	6,128	0
Conversion	0	0
Granted	80	6,208
Vested	0	0
Outstanding	6,208	6,208
Outstanding	$ 18	$ 0
Conversion	0	0
Granted	12.87	17.93
Vested	0	0
Outstanding	$ 17.93	$ 17.93

Stock And Unit-Based Compensa_6

Stock And Unit-Based Compensation - Summary of Stock and Unit Based Compensation Award Valuation Assumptions (Details)	6 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free rate	0.20%	0.14%
Volatility	40.00%	80.00%
Time to liquidity event (years)	3 years	2 years
Discount for lack of marketability (DLOM)	20	0

Stock And Unit-Based Compensa_7

Stock And Unit-Based Compensation - Summary of Class B Profits Interests Units (Details) - $ / shares shares in Thousands	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted- average grant date fair value, beginning balance	$ 0.13	$ 0	$ 0.13
Weighted- average grant date fair value, granted	0.13	0.13	0.16
Weighted- average grant date fair value, forfeited			0.13
Weighted- average grant date fair value, conversion			0.13
Weighted- average grant date fair value, ending balance	$ 0.13	$ 0.13	$ 0
Class B Profits Interests Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Class B profits interests outstanding, beginning balance	134,855	0	143,343
Class B profits interests outstanding, granted	627	135,482	9,522
Class B profits interests outstanding, forefeited			(245)
Class B profits interests outstanding, conversion			(152,620)
Class B profits interests outstanding, ending balance	135,482	135,482	0

Stock And Unit-Based Compensa_8

Stock And Unit-Based Compensation - Summary of Class B Profits Interests Units Corresponding Hurdle Values (Details) - shares shares in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Apr. 13, 2020
Class B Profits Interests Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units Outstanding	0	143,343	135,482	134,855	0

Stock And Unit-Based Compensa_9

Stock And Unit-Based Compensation - Summary of Class B Profits Interests General and Administrative Expenses (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021
Class B Profits Interests Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unit-based compensation expense	$ 573	$ 865	$ 1,135

Stockholders' Equity Members'_3

Stockholders' Equity Members' Deficit - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 14, 2021	Jun. 09, 2021	Sep. 30, 2021	Dec. 31, 2020	May 14, 2020	Apr. 13, 2020
Subsidiary Sale Of Stock [Line Items]
Issuance of common , Shares			1,687,000	1,044,509,000
Common Stock, Shares Authorized			800,000,000	0
Common Stock, par value			$ 0.01	$ 0.01
Common Unit, Outstanding			374,149,000	1,044,509,000		0
Fair Value Of Mezzanine Equity		$ 36,750
Conversion of Stock			723,267,000
Preferred Stock, Shares Authorized			25,000,000	0
Preferred Stock, par value			$ 0.01	$ 0.01
Preferred Stock, Shares Outstanding			0	0
Class A-1 Common Units [Member]
Subsidiary Sale Of Stock [Line Items]
Issuance of common , Shares			0	959,563,000
Common Unit, Outstanding			0	959,563,000	345,978,000	0
Conversion of Stock			(959,563,000)
Class A-2 Common Units [Member]
Subsidiary Sale Of Stock [Line Items]
Issuance of common , Shares			1,687,000	49,946,000
Common Unit, Outstanding			0	49,946,000	35,845,000	0
Conversion of Stock			(51,633,000)
Redeemable Class A Unit
Subsidiary Sale Of Stock [Line Items]
Issuance of common , Shares			0	35,000,000
Common Unit, Outstanding			0	35,000,000		0
Conversion of Stock			(35,000,000)
Redeemable Class A Unit | Chief Executive Officer
Subsidiary Sale Of Stock [Line Items]
Shares, Issued					35,000,000
Common Stock [Member]
Subsidiary Sale Of Stock [Line Items]
Common Unit, Outstanding			374,149,000			0
Conversion of Stock		10,234,000	340,849,000
IPO
Subsidiary Sale Of Stock [Line Items]
Shares Issued Price Per Share			$ 18
Preferred Stock, Shares Authorized					25,000,000
Preferred Stock, par value					$ 0.01
Preferred Stock, Shares Outstanding					0
IPO | LifeStance [Member]
Subsidiary Sale Of Stock [Line Items]
Issuance of common , Shares	32,800,000
IPO | Common Stock [Member]
Subsidiary Sale Of Stock [Line Items]
Issuance of common , Shares			32,800,000
IPO | Maximum
Subsidiary Sale Of Stock [Line Items]
Common Stock, Shares Authorized			800,000,000
IPO | Minimum
Subsidiary Sale Of Stock [Line Items]
Common Stock, Shares Authorized			1,000

Stockholders' Equity Members'_4

Stockholders' Equity Members' Deficit - Summary of Common Stock (Details) - shares shares in Thousands	Jun. 09, 2021	Sep. 30, 2021	Dec. 31, 2020
Subsidiary Sale Of Stock [Line Items]
Begining Balance		1,044,509	0
Issuance of common , Shares		1,687	1,044,509
Common Stock, Shares, Issued		374,149	0
Common Stock Shares Issued		374,149	0
Vested Class B Profits Interest		17,920
Conversion to common stock		(723,267)
Initial Public Offering		32,800
Endowment to the LifeStance Health Foundation		500
Ending Balance		374,149	1,044,509
Redeemable Class A Unit
Subsidiary Sale Of Stock [Line Items]
Begining Balance		35,000	0
Issuance of common , Shares		0	35,000
Vested Class B Profits Interest		0
Conversion to common stock		35,000
Initial Public Offering		0
Endowment to the LifeStance Health Foundation		0
Ending Balance		0	35,000
Class A-1 Common Units [Member]
Subsidiary Sale Of Stock [Line Items]
Begining Balance		959,563	0
Issuance of common , Shares		0	959,563
Vested Class B Profits Interest		0
Conversion to common stock		959,563
Initial Public Offering		0
Endowment to the LifeStance Health Foundation		0
Ending Balance		0	959,563
Class A-2 Common Units [Member]
Subsidiary Sale Of Stock [Line Items]
Begining Balance		49,946	0
Issuance of common , Shares		1,687	49,946
Vested Class B Profits Interest		0
Conversion to common stock		51,633
Initial Public Offering		0
Endowment to the LifeStance Health Foundation		0
Ending Balance		0	49,946
Class B Units [Member]
Subsidiary Sale Of Stock [Line Items]
Begining Balance		0	0
Issuance of common , Shares		0	0
Vested Class B Profits Interest		17,920
Conversion to common stock		17,920
Initial Public Offering		0
Endowment to the LifeStance Health Foundation		0
Ending Balance		0	0
Common Stock [Member]
Subsidiary Sale Of Stock [Line Items]
Begining Balance			0
Conversion to common stock	(10,234)	(340,849)
Initial Public Offering		32,800
Endowment to the LifeStance Health Foundation		500
Ending Balance		374,149

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Jun. 30, 2021USD ($)	Sep. 30, 2021Facility
Subsidiary Or Equity Method Investee [Line Items]
Number of office facilities | Facility			40
Clinicians expiration			2034
Termination Fee		$ 1,213
Management fee	$ 0

Related Party Transactions - Sc

Related Party Transactions - Schedule of Related Party Rent Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Related Party Transactions [Abstract]
Rent expense	$ 809	$ 262	$ 388	$ 369	$ 2,006

Related Party Transactions - _2

Related Party Transactions - Schedule of Future Minimum Operating Lease Payments (Details) $ in Thousands	Sep. 30, 2021USD ($)
Related Party Transactions [Abstract]
Remainder of 2021	$ 761
2022	2,973
2023	2,688
2024	2,415
2025	2,333
Thereafter	1,501
Total	$ 12,671

Related Party Transactions - _3

Related Party Transactions - Schedule of Related Party Management Fees (Details) - USD ($) $ in Thousands	3 Months Ended	4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Related Party Transactions [Abstract]
Management fees	$ 44	$ 14	$ 60	$ 1,445

Commitments and Contingencies -

Commitments and Contingencies - Summary of Contingent Consideration Balance (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Beginning Balance	$ 14,123	$ 10,951	$ 25,536	$ 0	$ 16,414
Additions related to TPG Acquisition				9,909
Additions related to acquisitions	2,775	1,035	3,788	4,226	5,514
Payments of contingent consideration	(675)	(100)	(19,093)	(2,300)	(6,262)
Loss (gain) on remeasurement	906	(89)	(322)	(38)	1,463
Ending Balance	$ 17,129	$ 11,797	$ 9,909	$ 11,797	$ 17,129

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Commitments And Contingencies Disclosure [Abstract]
Lease expiration year	2029
Medical malpractice insurance, coverage per claim limit	$ 8,000
Medical malpractice insurance, annual coverage per clinician	$ 12,000

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Third-party Rent Expense (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Loss Contingencies [Line Items]
Total rent expense	$ 8,429	$ 4,606	$ 4,210	$ 6,962	$ 22,533
Center Cost [Member]
Loss Contingencies [Line Items]
Total rent expense	8,302	4,484	4,082	6,779	21,878
General And Administrative Expense [Member]
Loss Contingencies [Line Items]
Total rent expense	$ 127	$ 122	$ 128	$ 183	$ 655

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Future Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2021USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Remainder of 2021	$ 761
2022	2,973
2023	2,688
2024	2,415
2025	2,333
Thereafter	1,501
Total	12,671
Contingent Consideration [Member]
Business Acquisition, Contingent Consideration [Line Items]
Remainder of 2021	6,391
2022	26,183
2023	25,093
2024	21,140
2025	17,072
Thereafter	33,724
Total	$ 129,603

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		4 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	May 14, 2020	Sep. 30, 2020	Sep. 30, 2021
Earnings Per Share [Abstract]
Net loss available to common stockholders'/members'	$ (120,452)	$ (3,294)	$ (298,189)	$ (7,636)	$ (235,917)
Weighted-average shares used to compute basic and diluted net loss per share	343,394	302,657		300,799	321,283
NET LOSS PER SHARE, BASIC AND DILUTED	$ (0.35)	$ (0.01)		$ (0.03)	$ (0.73)

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event [Member] - May 2020 Credit Agreement [Member] $ in Thousands	Oct. 01, 2021USD ($)
Business Acquisition [Line Items]
Cash consideration	$ 34,973
Maximum [Member]
Business Acquisition [Line Items]
Contingent consideration	$ 2,507