Histogen (HSTO) S-1/A 29 Dec 20 IPO registration (amended) Financial data

Cover

Cover	9 Months Ended
	Sep. 30, 2020
Cover [Abstract]
Document Type	S-1/A
Amendment Flag	false
Entity Registrant Name	Histogen Inc.
Entity Central Index Key	0001383701
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($)	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 6,649,000	$ 2,065,000	$ 3,027,000
Restricted cash	10,000	10,000
Accounts receivable, net	171,000	110,000
Inventories	453,000	106,000	939,000
Prepaid and other current assets	699,000	167,000
Total current assets	7,982,000	2,458,000
Restricted cash	250,000
Property and equipment, net	295,000	320,000	287,000
Right-of-use asset	4,334,000	95,000
Other assets	1,091,000	69,000
Total assets	13,952,000	2,942,000
Current liabilities
Accounts payable	1,130,000	808,000
Accrued liabilities	553,000	446,000	666,000
Accrued compensation	272,000	182,000	86,000
Current portion of Paycheck Protection Program loan	39,000
Current portion of lease liabilities	0	108,000
Current portion of deferred revenue	103,000	19,000
Total current liabilities	1,825,000	1,381,000
Noncurrent Paycheck Protection Program loan	428,000
Noncurrent portion of lease liabilities	4,749,000	0
Deferred rent, less current portion			89,000
Noncurrent portion of deferred revenue	123,000	138,000
Other liabilities	315,000	321,000	386,000
Total liabilities	7,440,000	1,840,000
Commitments and contingencies (Note 10)
Convertible preferred stock, $0.001 par value, authorized shares - 73,000,000 at December 31, 2019 and 2018; issued and outstanding shares - 35,184,882 and 33,561,102 at December 31, 2019 and 2018, respectively; liquidation preference - $40,294 and $37,915 at December 31, 2019 and 2018, respectively		39,070,000
Stockholders' deficit
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000 shares authorized; 3,317 shares and 3,316 shares issued and outstanding at December 31, 2019 and 2018, respectively	1,000
Additional paid-incapital	66,638,000	6,864,000
Accumulated deficit	(59,194,000)	(43,933,000)
Total Histogen Inc. stockholders' equity (deficit)	7,445,000	(37,069,000)
Noncontrolling interest	(933,000)	(899,000)
Total equity (deficit)	6,512,000	(37,968,000)	(35,520,000)
Total liabilities and stockholders' equity	$ 13,952,000	2,942,000
Previously Reported [Member]
Current assets
Cash and cash equivalents		2,065,000	3,027,000
Restricted cash		10,000	10,000
Accounts receivable, net		110,000	250,000
Inventories		106,000	939,000
Prepaid and other current assets		167,000	11,000
Total current assets		2,458,000	4,237,000
Property and equipment, net		320,000	287,000
Right-of-use asset		95,000
Other assets		69,000	223,000
Total assets		2,942,000	4,747,000
Current liabilities
Accounts payable		808,000	315,000
Accrued liabilities		446,000	666,000
Current portion of lease liabilities		108,000
Current portion of deferred revenue		19,000	1,545,000
Indemnification liability			239,000
Warrant liabilities			276,000
Total current liabilities		1,381,000	3,041,000
Noncurrent portion of deferred revenue		138,000	157,000
Other liabilities		321,000	386,000
Total liabilities		1,840,000	3,584,000
Commitments and contingencies (Note 10)
Convertible preferred stock, $0.001 par value, authorized shares - 73,000,000 at December 31, 2019 and 2018; issued and outstanding shares - 35,184,882 and 33,561,102 at December 31, 2019 and 2018, respectively; liquidation preference - $40,294 and $37,915 at December 31, 2019 and 2018, respectively		39,070,000	36,683,000
Stockholders' deficit
Common stock, $0.0001 par value; 200,000 shares authorized; 3,317 shares and 3,316 shares issued and outstanding at December 31, 2019 and 2018, respectively		23,000	23,000
Additional paid-incapital		6,841,000	6,288,000
Accumulated deficit		(43,933,000)	(40,967,000)
Total Histogen Inc. stockholders' equity (deficit)		(37,069,000)	(34,656,000)
Noncontrolling interest		(899,000)	(864,000)
Total equity (deficit)		(37,968,000)	(35,520,000)
Total liabilities and stockholders' equity		2,942,000	4,747,000
Predecessor Company [Member]
Current assets
Cash and cash equivalents		20,703,000	11,565,000
Marketable securities		0	29,127,000
Collaboration receivables		122,000	3,677,000
Prepaid and other current assets		781,000	3,057,000
Total current assets		21,606,000	47,426,000
Property and equipment, net			154,000
Right-of-use asset		221,000
Other assets		221,000	1,223,000
Total assets		21,827,000	48,803,000
Current liabilities
Accounts payable and accrued expenses		1,064,000	6,216,000
Accrued compensation		238,000	2,230,000
Current portion of lease liabilities		338,000
Current portion of deferred revenue			10,075,000
Total current liabilities		1,640,000	18,521,000
Deferred revenue, less current portion			2,815,000
Deferred rent, less current portion			68,000
Stockholders' deficit
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding
Additional paid-incapital		218,201,000	214,045,000
Accumulated other comprehensive loss			(17,000)
Accumulated deficit		(198,014,000)	(186,629,000)
Total Histogen Inc. stockholders' equity (deficit)		20,187,000	27,399,000
Total equity (deficit)		20,187,000	27,399,000
Total liabilities and stockholders' equity		$ 21,827,000	$ 48,803,000

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	0	73,000,000
Convertible preferred stock, shares issued	0	5,046,154
Convertible preferred stock, shares outstanding	0	5,046,154	4,813,274
Convertible preferred stock, liquidation preference	$ 0	$ 40,294
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	105,000,000
Common stock, shares issued	12,487,973	3,343,356
Common stock, shares outstanding	12,487,973	3,343,356
Previously Reported [Member]
Convertible preferred stock, par value		$ 0.001	$ 0.001
Convertible preferred stock, shares authorized		73,000,000	73,000,000
Convertible preferred stock, shares issued		35,184,882	33,561,102
Convertible preferred stock, shares outstanding		35,184,882	33,561,102
Convertible preferred stock, liquidation preference		$ 40,294	$ 37,915
Common stock, par value		$ 0.001	$ 0.001
Common stock, shares authorized		105,000,000	105,000,000
Common stock, shares issued		23,311,656	22,954,293
Common stock, shares outstanding		23,311,656	22,954,293
Predecessor Company [Member]
Preferred stock, par value		$ 0.0001	$ 0.0001
Preferred stock, shares authorized		10,000,000	10,000,000
Preferred stock, shares issued		0	0
Preferred stock, shares outstanding		0	0
Common stock, par value		$ 0.0001	$ 0.0001
Common stock, shares authorized		200,000,000	200,000,000
Common stock, shares issued		33,170,000	33,165,000
Common stock, shares outstanding		33,170,000	33,165,000

Unaudited Condensed Consolidate

Unaudited Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Total revenue	$ 495,000	$ 314,000		$ 1,581,000	$ 9,893,000	$ 11,454,000	$ 1,777,000
Operating expense
Research and development	1,534,000	673,000		4,362,000	2,716,000	6,345,000	3,490,000
General and administrative	1,982,000	1,202,000		4,753,000	4,607,000	6,212,000	3,184,000
Total operating expense	3,841,000	2,060,000		16,931,000	10,683,000	14,772,000	7,418,000
Loss from operations	(3,346,000)	(1,746,000)		(15,350,000)	(790,000)	(3,318,000)	(5,641,000)
Acquired in-processresearch and development				7,144,000	2,250,000
Other income (expense)
Interest income						42,000	(42,000)
Change in fair value of indemnification liability	108,000			108,000			(57,000)
Total other income	83,000	48,000		55,000	113,000
Inducement expense							(375,000)
Change in fair value of warrant liabilities		30,000			77,000	276,000	(47,000)
Loss before income taxes						$ (3,000,000)	$ (6,162,000)
Interest income (expense), net	$ (25,000)	$ 18,000		$ (53,000)	$ 36,000
Other comprehensive income (loss):
Net loss per share attributable to common stockholders, basic and diluted	$ (0.27)	$ (0.51)		$ (2.06)	$ (0.20)	$ (0.13)	$ (0.27)
Weighted average shares outstanding used in computing net loss per share, basic and diluted	12,169,173	3,343,356		7,425,051	3,328,549	23,234,436	22,771,508
Loss from operations	$ (3,346,000)	$ (1,746,000)		$ (15,350,000)	$ (790,000)	$ (3,318,000)	$ (5,641,000)
Income tax expense						1,000	1,000
Net loss	(3,263,000)	(1,698,000)		(15,295,000)	(677,000)	(3,001,000)	(6,163,000)
Loss attributable to noncontrolling interest	(14,000)	(4,000)		(34,000)	(21,000)	(35,000)	(38,000)
Net loss attributable to common stockholders	(3,249,000)	(1,694,000)		(15,261,000)	(656,000)	(2,966,000)	(6,125,000)
Predecessor Company [Member]
Revenue
Total revenue		3,376,000				21,717,000	33,586,000	$ 35,377,000
Operating expense
Research and development						23,527,000	41,368,000	43,220,000
General and administrative						10,196,000	10,495,000	9,707,000
Total operating expense		6,759,000				33,723,000	51,863,000	52,927,000
Loss from operations						(12,006,000)	(18,277,000)	(17,550,000)
Other income (expense)
Interest income						568,000	962,000	892,000
Interest expense							(696,000)	(662,000)
Change in fair value of indemnification liability						53,000	1,000	(76,000)
Total other income		130,000				621,000	267,000	154,000
Net loss		$ (3,253,000)				(11,385,000)	(18,010,000)	(17,396,000)
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities						17,000	60,000	(71,000)
Comprehensive loss						$ (11,368,000)	$ (17,950,000)	$ (17,467,000)
Net loss per share attributable to common stockholders, basic and diluted		$ (0.98)	[1]			$ (3.43)	$ (5.93)	$ (6.08)
Weighted average shares outstanding used in computing net loss per share, basic and diluted						3,317,000	3,037,000	2,859,000
Loss from operations						$ (12,006,000)	$ (18,277,000)	$ (17,550,000)
Net loss						(11,385,000)	(18,010,000)	(17,396,000)
License [Member]
Revenue
Total revenue	5,000	$ 5,000		877,000	7,515,000	7,519,000	19,000
Product [Member]
Revenue
Total revenue	419,000	190,000		419,000	1,956,000	3,415,000	1,254,000
Operating expense
Cost of product revenue	263,000	81,000		424,000	873,000	1,893,000	561,000
Grant [Member]
Revenue
Total revenue	0	0		0	150,000	150,000	300,000
Service [Member]
Revenue
Total revenue	71,000	119,000		285,000	272,000	370,000	204,000
Operating expense
Cost of product revenue	$ 62,000	$ 104,000		$ 248,000	$ 237,000	322,000	183,000
Collaboration [Member] | Predecessor Company [Member]
Revenue
Total revenue						$ 21,717,000	$ 33,586,000	$ 35,377,000
[1]	Net loss per share is computed independently for each quarter and the full year based upon respective shares outstanding; therefore, the sum of the quarterly net loss per share amounts may not equal the annual amounts reported.

Unaudited Condensed Consolida_2

Unaudited Condensed Consolidated Statements of Convertible Preferred Stock and Stockholder's Equity (Deficit) - USD ($) $ in Thousands	Total	Predecessor Company [Member]	Previously Reported [Member]	Common Stock [Member]	Common Stock [Member]Predecessor Company [Member]	Common Stock [Member]Previously Reported [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Predecessor Company [Member]	Additional Paid-in Capital [Member]Previously Reported [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Predecessor Company [Member]	Accumulated Deficit [Member]Previously Reported [Member]	Total Histogen Inc. Stockholders' Deficit [Member]	Total Histogen Inc. Stockholders' Deficit [Member]Previously Reported [Member]	Noncontrolling Interest [Member]	Noncontrolling Interest [Member]Previously Reported [Member]	AOCI Attributable to Parent [Member]Predecessor Company [Member]	Convertible Preferred Stock Series B [Member]	Convertible Preferred Stock Series B [Member]Previously Reported [Member]	Convertible Preferred Stock Series D [Member]	Convertible Preferred Stock Series D [Member]Previously Reported [Member]	Convertible Preferred Stock Series D for Clinical Service [Member]Previously Reported [Member]	PUR Settlement [Member]	PUR Settlement [Member]Previously Reported [Member]
Beginning balance at Dec. 31, 2016		$ 21,789						$ 172,428			$ (150,633)						$ (6)
Beginning balance, shares at Dec. 31, 2016					2,612,000
Issuance of common stock upon exercise of stock options		$ 104						104
Issuance of common stock upon exercise of stock options, shares		7,000			7,000
Issuance of common stock for employee stock purchase plan		$ 65						65
Issuance of common stock for employee stock purchase plan, shares					2,000
Share-based compensation		4,098						4,076			22
Ending balance at Dec. 31, 2017			$ 30,064
Ending balance, shares at Dec. 31, 2017			29,226,935
Issuance of common stock for Lordship Indemnification		30,610						30,610
Issuance of common stock for Lordship Indemnification, shares					598,000
Repurchase of common stock		(11,203)						(11,203)
Repurchase of common stock, shares					(217,000)
Net income		(17,396)									(17,396)
Unrealized gain (loss) on marketable securities		(71)															(71)
Ending balance at Dec. 31, 2017	$ (29,660)	27,996		$ 22			$ 5,986	196,080		$ (34,842)	(168,007)		$ (28,834)		$ (826)		(77)
Ending balance, shares at Dec. 31, 2017				22,227,930	3,002,000
Issuance of convertible preferred stock																			$ 4,005		$ 2,101	$ 513
Issuance of convertible preferred stock, shares																		114,445	2,592,000	1,742,167	1,400,500	341,667
Issuance of common stock upon exercise of stock options	77	$ 362		$ 1			76	362					77
Issuance of common stock upon exercise of stock options, shares		22,000		726,363	22,000
Issuance of common stock for employee stock purchase plan		$ 117						117
Purchase of subsidiary shares from noncontrolling interest	(100)						(100)						(100)
Issuance of common stock for employee stock purchase plan, shares					4,000
Share-based compensation	326	3,757					326	3,757					326
Conversion of convertible note payable to common stock		13,729						13,729
Conversion of convertible note payable to common stock, shares					288,000
Ending balance at Dec. 31, 2018	$ 36,683		$ 36,683																$ 9,232		$ 12,415
Ending balance, shares at Dec. 31, 2018	4,813,274		33,561,102
Cumulative effect of adoption of accounting standard		(612)									(612)
Net income	$ (6,163)	(18,010)								(6,125)	(18,010)		(6,125)		(38)
Unrealized gain (loss) on marketable securities		60															60
Ending balance at Dec. 31, 2018	(35,520)	27,399	$ (35,520)			$ 23	6,311	214,045	$ 6,288	(40,967)	(186,629)	$ (40,967)	(34,656)	$ (34,656)	(864)	$ (864)	(17)
Ending balance, shares at Dec. 31, 2018				3,292,104	3,316,000	22,954,293
Issuance of convertible preferred stock																		$ 124		$ 513			$ 1,750
Issuance of convertible preferred stock, shares																		16,413		49,144			167,323
Issuance of common stock upon exercise of stock options, shares				29,367
Share-based compensation	329						329						329
Ending balance at Sep. 30, 2019	$ 39,070
Ending balance, shares at Sep. 30, 2019	5,046,154
Issuance of common stock for Lordship Indemnification	$ 115						115						115
Issuance of common stock for Lordship Indemnification, shares				21,885
Net income	(677)									(656)			(656)		(21)
Ending balance at Sep. 30, 2019	(35,753)						6,755			(41,623)			(34,868)		(885)
Ending balance, shares at Sep. 30, 2019				3,343,356
Beginning balance at Dec. 31, 2018	(35,520)	27,399	(35,520)			$ 23	6,311	214,045	6,288	(40,967)	(186,629)	(40,967)	(34,656)	(34,656)	(864)	(864)	(17)
Beginning balance at Dec. 31, 2018	$ 36,683		$ 36,683																9,232		12,415
Issuance of convertible preferred stock																			$ 124		$ 513			$ 1,750
Beginning balance, shares at Dec. 31, 2018				3,292,104	3,316,000	22,954,293
Beginning balance, shares at Dec. 31, 2018	4,813,274		33,561,102
Issuance of convertible preferred stock, shares																		2,592,000	114,445	1,509,335	342,668			1,166,667
Issuance of common stock upon exercise of stock options, shares				204,769
Issuance of common stock for employee stock purchase plan		3						3
Issuance of common stock for employee stock purchase plan, shares					1,000
Share-based compensation	$ 438	4,153					438	4,153					438
Ending balance at Dec. 31, 2019	$ 39,070		$ 39,070																$ 9,356		$ 14,678
Ending balance, shares at Dec. 31, 2019	5,046,154		35,184,882
Issuance of common stock for Lordship Indemnification	$ 115						115						115
Issuance of common stock for Lordship Indemnification, shares				152,594
Net income	(3,001)	(11,385)								(2,966)	(11,385)		(2,966)		(35)
Unrealized gain (loss) on marketable securities		17															$ 17
Ending balance at Dec. 31, 2019	(37,968)	20,187	$ (37,968)			$ 23	6,864	218,201	6,841	(43,933)	(198,014)	(43,933)	(37,069)	(37,069)	(899)	(899)
Ending balance, shares at Dec. 31, 2019				3,343,356	3,317,000	23,311,656
Beginning balance at Jun. 30, 2019	(34,170)						6,640			(39,929)			(33,289)		(881)
Beginning balance at Jun. 30, 2019	$ 39,070
Beginning balance, shares at Jun. 30, 2019				3,327,198
Beginning balance, shares at Jun. 30, 2019	5,046,154
Share-based compensation	$ 115						115						115
Ending balance at Sep. 30, 2019	$ 39,070
Ending balance, shares at Sep. 30, 2019	5,046,154
Issuance of common stock for Lordship Indemnification, shares				16,158
Net income	$ (1,698)									(1,694)			(1,694)		(4)
Ending balance at Sep. 30, 2019	(35,753)						6,755			(41,623)			(34,868)		(885)
Ending balance, shares at Sep. 30, 2019				3,343,356
Beginning balance at Dec. 31, 2019	(37,968)	$ 20,187	(37,968)			$ 23	6,864	$ 218,201	$ 6,841	(43,933)	$ (198,014)	$ (43,933)	(37,069)	$ (37,069)	(899)	$ (899)
Beginning balance at Dec. 31, 2019	$ 39,070		$ 39,070																$ 9,356		$ 14,678
Beginning balance, shares at Dec. 31, 2019				3,343,356	3,317,000	23,311,656
Beginning balance, shares at Dec. 31, 2019	5,046,154		35,184,882
Issuance of common stock upon exercise of stock options	$ 40						40						40
Issuance of common stock upon exercise of stock options, shares				28,684
Issuance of common stock to former stockholders of Conatus upon Merger	18,872						18,872						18,872
Issuance of common stock to former stockholders of Conatus upon Merger, shares				3,394,299
Share-based compensation	456						456						456
Conversion of convertible note payable to common stock	$ 39,070			$ 1			39,069						39,070
Conversion of convertible note payable to common stock, shares	5,046,154			5,046,154
Ending balance at Sep. 30, 2020	$ 0
Ending balance, shares at Sep. 30, 2020	0
Issuance of common stock for Lordship Indemnification	$ 1,337						1,337						1,337
Issuance of common stock for Lordship Indemnification, shares				675,480
Net income	(15,295)									(15,261)			(15,261)		(34)
Ending balance at Sep. 30, 2020	6,512			$ 1			66,638			(59,194)			7,445		(933)
Ending balance, shares at Sep. 30, 2020				12,487,973
Beginning balance at Jun. 30, 2020	8,313			$ 1			65,176			(55,945)			9,232		(919)
Beginning balance, shares at Jun. 30, 2020				11,812,493
Share-based compensation	125						125						125
Ending balance at Sep. 30, 2020	$ 0
Ending balance, shares at Sep. 30, 2020	0
Issuance of common stock for Lordship Indemnification	$ 1,337						1,337						1,337
Issuance of common stock for Lordship Indemnification, shares				675,480
Net income	(3,263)									(3,249)			(3,249)		(14)
Ending balance at Sep. 30, 2020	$ 6,512			$ 1			$ 66,638			$ (59,194)			$ 7,445		$ (933)
Ending balance, shares at Sep. 30, 2020				12,487,973

Unaudited Condensed Consolida_3

Unaudited Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net loss	$ (1,698)	$ (15,295)	$ (677)	$ (3,001)	$ (6,163)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Acquired in-processresearch and development		7,144	1,750
Depreciation and amortization	40	74	107	145	150
Stock-based compensation		456	329	438	326
Loss on disposal of property and equipment			7	6
Series D convertible preferred stock issued for PUR Settlement				1,750
Series D convertible preferred stock issued for clinical services					363
Inducement expense					375
Write-off of inventory		186		155
Change in fair value of indemnification liability					26
Change in fair value of warrant liabilities	(30)		(77)	(276)	47
Changes in operating assets and liabilities:
Accounts receivable		(61)	120	140	(179)
Inventories		(533)	(133)	678	(502)
Prepaid and other current assets		(122)	(107)	(156)	8
Other assets		(127)	82	154	31
Accounts payable		(197)	132	493	(368)
Accrued liabilities		80	(256)	(196)	(360)
Right-of-use asset and lease liabilities, net		346	(56)	(76)
Deferred revenue		69	(826)	(1,545)	(313)
Other liabilities					(57)
Net cash (used in) provided by operating activities		(7,980)	395	(1,291)	(6,616)
Cash flows from investing activities
Cash acquired in connection with the Merger		12,835
Cash paid for acquisition related costs		(1,811)
Capital expenditures		(49)	(152)	(152)	(126)
Purchase of subsidiary shares from noncontrolling interest					(100)
Net cash provided by (used in) investing activities		10,975	(152)	(152)	(226)
Cash flows from financing activities
Repayment of notes payable to related parties				(7)	(449)
Repayment of finance lease obligations		(5)	(25)	(25)	(30)
Proceeds from issuance of common stock, net		1,337
Proceeds from promissory notes		500
Payments on promissory notes		(500)
Proceeds from exercise of stock options		40			67
Proceeds from Payroll Protection Program Loan		467
Net cash provided by financing activities		1,839	488	481	1,689
Net (decrease) increase in cash and cash equivalents		4,834	731	(962)	(5,153)
Cash and cash equivalents at beginning of period		2,075	3,037	3,037	8,190
Cash and cash equivalents at end of period	3,768	6,909	3,768	2,075	3,037	$ 8,190
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets
Cash and cash equivalents	3,758	6,649	3,758	2,065	3,027
Restricted cash	10	260	10	10	10
Total cash, cash equivalents and restricted cash	$ 3,768	6,909	3,768	2,075	3,037
Supplemental disclosure of cash flow information
Cash paid for interest				7	67
Cash paid for income taxes				0	0
Noncash investing and financing activities
Right-of-use asset		4,481	619	619
Right-of-use asset obtained in exchange for finance lease liability			40	40
Conversion of convertible preferred stock into common stock		39,070
Issuance of common stock to Conatus stockholders		18,872
Issuance of common stock for settlement of trade payables					10
Net assets acquired in Merger		710
Acquisition related costs included in accounts payable		6
Issuance for Lordship Indemnification (Note 11)			115	115
Predecessor Company [Member]
Cash flows from operating activities
Net loss				(11,385)	(18,010)	(17,396)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation				73	91	108
Stock-based compensation				4,153	3,757	4,098
Amortization of premiums and discounts on marketable securities, net				(204)	(341)	(68)
Write off of property and equipment and other assets				210
Impairment of right-of-use asset				50
Accrued interest included in convertible note payable					696	658
Changes in operating assets and liabilities:
Collaboration receivables				3,555	(310)	(867)
Prepaid and other current assets				642	480	(123)
Other assets					(537)	(872)
Accounts payable and accrued expenses				(2,355)	(5,760)	6,638
Accrued compensation				(1,992)	222	(343)
Deferred revenue				(12,890)	(15,099)	(25,010)
Lease liabilities, net				(59)
Deferred rent					(46)	(32)
Net cash (used in) provided by operating activities				(20,202)	(34,857)	(33,209)
Cash flows from investing activities
Maturities of marketable securities				44,842	69,685	81,877
Purchase of marketable securities				(15,494)	(39,637)	(121,723)
Capital expenditures				(11)	(66)	(25)
Net cash provided by (used in) investing activities				29,337	29,982	(39,871)
Cash flows from financing activities
Proceeds from issuance of convertible note payable, net						12,500
Principal payment on promissory note						(1,000)
Proceeds from issuance of common stock, net						30,610
Repurchase of common stock						(11,203)
Deferred financing costs					(118)
Proceeds from stock issuances related to exercise of stock options and employee stock purchase plan				3	479	169
Net cash provided by financing activities				3	361	31,076
Net (decrease) increase in cash and cash equivalents				9,138	(4,514)	(42,004)
Cash and cash equivalents at beginning of period		$ 20,703	11,565	11,565	16,079	58,083
Cash and cash equivalents at end of period				20,703	11,565	16,079
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets
Cash and cash equivalents				20,703	11,565
Supplemental disclosure of cash flow information
Cash paid for interest						$ 5
Noncash investing and financing activities
Conversion of convertible note payable to common stock					13,729
Right-of-use asset				590
Series D Convertible Preferred Stock [Member]
Cash flows from financing activities
Proceeds from the issuance of Series D convertible preferred stock, net			513	513	2,101
Series B Preferred Stock [Member]
Noncash investing and financing activities
Issuance of Series B convertible preferred stock for note payable and accrued interest					$ 4,005
Issuance for Lordship Indemnification (Note 11)			$ 124	$ 124

Description of Business, Basis

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	1. Description of Business, Basis of Presentation and Summary of Significant Accounting Policies Description of Business Histogen Inc. (the “Company,” “Histogen,” or the “combined company”), formerly known as Conatus Pharmaceuticals Inc. (“Conatus”), was incorporated in the state of Delaware on July 13, 2005. The Company is a clinical-stage therapeutics company focused on developing potential first-in-class The Company’s lead drug candidate, HST-001, HST-001 HST-002 HST-003 non-prescription pan-caspase COVID-19 Merger between Private Histogen and Conatus Pharmaceuticals Inc. and Name Change On January 28, 2020, the Company, then operating as Conatus, entered into an Agreement and Plan of Merger and Reorganization, as amended (the “Merger Agreement”), with privately-held Histogen Inc. (“Private Histogen”) and Chinook Merger Sub, Inc., a wholly-owned subsidiary of the Company (“Merger Sub”). Under the Merger Agreement, Merger Sub merged with and into Private Histogen, with Private Histogen surviving as a wholly-owned subsidiary of the Company (the “Merger”). On May 26, 2020, the Merger was completed. Conatus changed its name to Histogen Inc., and Private Histogen, which remains as a wholly-owned subsidiary of the Company, changed its name to Histogen Therapeutics Inc. On May 27, 2020, the combined company’s common stock began trading on The Nasdaq Capital Market under the ticker symbol “HSTO”. Except as otherwise indicated, references herein to “Histogen,” the “Company,” or the “combined company”, refer to Histogen Inc. on a post-Merger basis, and the term “Private Histogen” refers to the business of privately-held Histogen Inc., prior to completion of the Merger. References to Conatus refer to Conatus Pharmaceuticals Inc. prior to completion of the Merger. Pursuant to the terms of the Merger Agreement, each outstanding share of Private Histogen common stock outstanding immediately prior to the closing of the Merger was converted into approximately 0.14342 shares of Company common stock (the “Exchange Ratio”), after taking into account the Reverse Stock Split, as defined below. Immediately prior to the closing of the Merger, all shares of Private Histogen preferred stock then outstanding were exchanged into shares of common stock of Private Histogen. In addition, all outstanding options exercisable for common stock of Private Histogen and warrants exercisable for common stock of Private Histogen became options and warrants exercisable for the same number of shares of common stock of the Company multiplied by the Exchange Ratio. Immediately following the Merger, stockholders of Private Histogen owned approximately 71.3% of the outstanding common stock of the combined company. The transaction was accounted for as a reverse asset acquisition in accordance with generally accepted accounting principles in the United States of America (“GAAP”). Under this method of accounting, Private Histogen was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the facts that, immediately following the Merger: (i) Private Histogen’s stockholders owned a substantial majority of the voting rights in the combined company, (ii) Private Histogen designated a majority of the members of the initial board of directors of the combined company, and (iii) Private Histogen’s senior management holds all key positions in the senior management of the combined company. As a result, as of the closing date of the Merger, the net assets of the Company were recorded at their acquisition-date relative fair values in the accompanying condensed consolidated financial statements of the Company and the reported operating results prior to the Merger are those of Private Histogen. Reverse Stock Split and Exchange Ratio On May 26, 2020, in connection with, and prior to the completion of, the Merger, the Company effected a one-for-ten Liquidity and Going Concern From inception and through September 30, 2020, the Company has accumulated losses of $59.2 million and expects to incur operating losses and generate negative cash flows from operations for the foreseeable future. As of September 30, 2020, the Company had $6.6 million in cash and cash equivalents. The Company has not yet established ongoing sources of revenues sufficient to cover its operating costs and will need to continue to raise additional capital to support its future operating activities, including progression of its development programs, preparation for commercialization, and other operating costs. Management’s plans with regard to these matters include entering into a combination of additional debt or equity financing arrangements, government funding, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. In addition, the Company may fund its losses from operations through the common stock purchase agreement the Company entered into with Lincoln Park in July 2020, for the purchase of up to $10.0 million of the Company’s common stock over the 24 month period of the purchase agreement, $8.5 million of which remains available for sale as of the date these condensed consolidated financial statements were available to be issued (see Note 9), subject to limitations on the amount of securities the Company may sell under its effective registration statement on Form S-3 The condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. Based on the above, there is substantial doubt about the Company’s ability to continue as a going concern within one year from the date the condensed consolidated financial statements are available to be issued. The condensed consolidated financial statements do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the outcome of this uncertainty. Basis of Presentation and Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its controlled subsidiaries, including Histogen Therapeutics, Inc., and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). All intercompany balances and transactions have been eliminated upon consolidation. The Company acquired Centro De Investigacion de Medicina Regenerativa, S.A. de C.V. (“CIMRESA”), a company in Mexico, during 2018 to facilitate a potential clinical development program for HSC. This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to FDA). CIMRESA had no operational or financial activity for the three and nine months ended September 30, 2020 and 2019. The Company holds a majority interest in Adaptive Biologix, Inc. (“AB”, formerly Histogen Oncology, LLC). AB was formed to develop and market applications for the treatment of cancer. The Company consolidates AB into its condensed consolidated financial statements. Reclassifications Certain prior period amounts related to the acquisition of in-process in-process Unaudited Interim Financial Information The unaudited condensed consolidated financial statements as of September 30, 2020, and for the three and nine months ended September 30, 2020 and 2019, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) and GAAP. Accordingly, these condensed consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of Management, these unaudited interim condensed consolidated financial statements contain all adjustments necessary, all of which are of a normal and recurring nature, to present fairly the Company’s financial position, results of operations and cash flows. Interim results are not necessarily indicative of results for a full year or future periods. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended December 31, 2019 included in our prospectus dated April 1, 2020, filed with the Securities and Exchange Commission pursuant to Rule 424(b) under the Securities Act, relating to the Registration Statement on Form S-4, No. 333-236332). Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the periods presented. Management believes that these estimates and assumptions are reasonable, however, actual results may differ and could have a material effect on future results of operations and financial position. Though the impact of the COVID-19 Significant estimates and assumptions include the useful lives of property and equipment, discount rates used in recognizing contracts containing leases, unrecognized tax benefits, reserves for excess or obsolete inventory, stock-based compensation, and best estimate of standalone selling price of revenue deliverables. Actual results may materially differ from those estimates. Variable Interest Entities The Company determined that AB is a variable interest entity (“VIE”) and that the Company is its primary beneficiary. The Company holds greater than 50% of the shares and has the authority to manage the business and affairs of the VIE. AB’s other shareholder does not have a controlling interest. On January 12, 2018, AB was converted into a traditional C corporation, a Delaware corporation, under a Plan of Conversion agreement between the Company and the other member of the limited liability company, Wylde, LLC (“Wylde”). The entity structure change eliminated some of the special rights Wylde had under the LLC charter and gave the Company more control over the voting rights under the new corporate structure. The Plan of Conversion called for 3,800,000 common stock shares of AB to be issued to the Company and Wylde in proportion to their interest in the LLC immediately before the agreement was executed. Contemporaneously, the Company offered to purchase, and Wylde agreed to sell, 100,000 of the AB common shares for $1.00 per share for a total price of $0.1 million. The completion of this transaction among the stockholders of AB resulted in Histogen owning 2,600,000 common shares or approximately 68% of AB. A VIE is typically an entity for which the Company has less than a 100% equity interest but controls the decision making over the business and affairs of the entity, directs the decisions driving the economic performance of such entity and participates in the profit and losses of such an entity. The Company weighed both quantitative and qualitative information about the different risks and reward characteristics of each entity and the significance of that entity to the consolidating group in the aggregate. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with an original maturity date of ninety days or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking, money market accounts and brokerage accounts. The Company’s current restricted cash consists of cash held as collateral for the issuer of its credit card accounts. Noncurrent restricted cash consists of collateral for a letter of credit issued as a security deposit for the lease of the Company’s headquarters and is required to be held throughout the lease term. Risks and Uncertainties Credit Risk At certain times throughout the year, the Company may maintain deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institutions in which those deposits are held. Customer Risk During the three months ended September 30, 2020 and 2019, one customer accounted for 100% and 39% of total revenues, respectively. During the nine months ended September 30, 2020 and 2019, one customer accounted for 100% and 94% of total revenues, respectively. Accounts receivable from the customer was $0.1 million at September 30, 2020 and December 31, 2019. COVID-19 On January 30, 2020, the World Health Organization (“WHO”) announced a global health emergency because of a new strain of coronavirus originating in Wuhan, China (the “COVID-19 outbreak”) and the risks to the international community as the virus spreads globally beyond its point of origin. In March 2020, the WHO classified the COVID-19 outbreak as a pandemic, based on the rapid increase in exposure globally. The full impact of the COVID-19 outbreak continues to evolve as of the date these condensed consolidated financial statements were available to be issued. As such, it is uncertain as to the full magnitude that the pandemic will have on the Company’s financial condition, liquidity, and future results of operations. Management is actively monitoring the situation on its financial condition, liquidity, operations, customers, suppliers, industry, and workforce. Given the daily evolution of the COVID-19 outbreak and the response to curb its spread, the Company is not able to estimate the effects of the COVID-19 outbreak to its results of operations, financial condition, or liquidity for fiscal year 2020. On March 27, 2020, President Trump signed into law the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”). The CARES Act, among other things, includes provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations, increased limitations on qualified charitable contributions and technical corrections to tax depreciation methods for qualified improvement property. The Company continues to examine the impact that the CARES Act may have on its business. Currently, the Company is unable to determine the impact that the CARES Act will have on its financial condition, results of operations, or liquidity. The CARES Act also appropriated funds for the U.S. Small Business Administration Paycheck Protection Program (“PPP”) loans that are forgivable in certain situations to promote continued employment, as well as Economic Injury Disaster Loans to provide liquidity to small businesses harmed by COVID-19. Refer to Note 8 — Paycheck Protection Program Loan for further information. Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. The allowance is based on an analysis of historical bad debt, current receivables aging and expected future write-offs of uncollectible accounts, as well as an assessment of specific identifiable accounts considered at risk or uncollectible. Additions to the allowance for doubtful accounts include provisions for bad debt and deductions from the allowance for doubtful accounts include customer write-offs. Provision for doubtful accounts was not material for all periods presented. Inventories Inventories, consisting of raw materials, work in process, and finished goods, are valued at the lower of cost (first-in, first-out Property and Equipment Property and equipment are reported net of accumulated depreciation and amortization and are comprised of office furniture and equipment, lab and manufacturing equipment, and leasehold improvements. Ordinary maintenance and repairs are charged to expense, while expenditures that extend the physical or economic life of the assets are capitalized. Furniture and all equipment are depreciated over their estimated useful lives, or five years, using the straight-line method. Leasehold improvements are amortized over their estimated useful lives and limited by the remaining term of the building lease, using the straight-line method. Valuation of Long-Lived Assets Long-lived assets to be held and used, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. As of September 30, 2020, the Company has not recognized any impairment to long-lived assets. Forward Purchase Contract In late 2011, Private Histogen contracted for research services from EPS Global Research Pte. Ltd. (“EPS”) to conduct clinical trials and compile data from a study that took place in 2011 and 2013. The unpaid amount due for the services was approximately $0.3 million. On January 26, 2017, Private Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby Private Histogen paid $50,000 and issued EPS 14,342 shares of Series D convertible preferred stock. The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $0.3 million at September 30, 2020 and December 31, 2019, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. The Company has the sole option to initiate the timing of the repurchase of the shares (which were converted into shares of common stock upon the Merger) before the deadline date. The Settlement Agreement was treated as debt subject to Accounting Standards Codification (“ASC”) 470, Debt Distinguishing Liabilities from Equity The Company determined the fair value of the liability to be approximately $0.3 million which is the value as if the repurchase commitment was exercised immediately. As of September 30, 2020 and December 31, 2019, the fair value of the EPS forward contract remained at approximately $0.3 million and is included in other liabilities in the accompanying condensed consolidated balance sheets. Convertible Preferred Stock Prior to the Merger, Private Histogen had shares of convertible preferred stock outstanding that were conditionally redeemable, as the redemption rights were either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control, and were classified as temporary equity. Comprehensive Income (Loss) The Company is required to report all components of comprehensive income (loss), including net income (loss), in the accompanying condensed consolidated financial statements in the period in which they are recognized. Comprehensive income (loss) is defined as the change in equity during a period from transactions and other events and circumstances from non-owner Revenue Recognition Product and License Revenue The Company records revenue in accordance with ASC 606, Revenue from Contracts with Customers Grant Awards In March 2017, the National Science Foundation (“NSF”), a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange 958-605, Not-for-Profit In September 2020, the Company was approved for a grant award from the U.S. Department of Defense (“DoD”) in the amount of approximately $2.0 million to partially fund the Company’s planned Phase 1/2 clinical trial of HST-003 Professional Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable. Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition. Cost of Professional Services Revenue Cost of professional services revenue represents the Company’s costs for full-time employee equivalents and actual out-of-pocket Research and Development Expenses All research and development costs are charged to expense as incurred. Research and development expenses primarily include (i) payroll and related costs associated with research and development performed, (ii) costs related to clinical and preclinical testing of the Company’s technologies under development, and (iii) other research and development costs including allocations of facility costs. Acquired In-Process The Company has acquired and may continue to acquire the rights to drug candidates in various stages of development. The up-front in-process General and Administrative Expenses General and administrative expenses represent personnel costs for employees involved in general corporate functions, including finance, accounting, legal and human resources, among others. Additional costs included in general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, charitable contributions, recruiting, allocated facility and general information technology costs, depreciation and amortization, and other general corporate overhead expenses. Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying condensed consolidated statements of operations. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income taxes are recorded for temporary differences between consolidated financial statement carrying amounts and the tax basis of assets and liabilities. Deferred tax assets and liabilities reflect the tax rates expected to be in effect for the years in which the differences are expected to reverse. No income tax expense or benefit was recorded for the three and nine months ended September 30, 2020 and 2019, due to the full valuation allowance on the Company’s net deferred tax assets. A valuation allowance is provided if it is more likely than not that some or all the deferred tax assets will not be realized. The Company also follows the provisions of accounting for uncertainty in income taxes which prescribes a model for the recognition and measurement of a tax position taken or expected to be taken in a tax return, and provides guidance on derecognition, classification, interest and penalties, disclosure and transition. The Company’s policy is to recognize interest or penalties related to income tax matters in income tax expense. Interest and penalties related to income tax matters were not material for the periods presented. Net Loss Per Share Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For the three and nine months ended September 30, 2020 and 2019, diluted net loss per share attributable to common stockholders is equal to basic net loss per share attributable to common stockholders as common stock equivalent shares from stock options and convertible preferred stock were anti-dilutive. The following table sets forth outstanding potentially dilutive shares that have been excluded from the calculation of diluted net loss per share attributable to common stockholders because of their anti-dilutive effect (in common stock equivalents): September 30, September 30, Outstanding stock options 1,499,123 1,358,588 Convertible preferred stock — 5,046,213 Warrants to purchase common stock 4,929 3,585 Warrants to purchase convertible preferred stock — 107,565 Total 1,504,052 6,515,951 Common Stock Valuations Prior to the Merger, the Company was required to periodically estimate the fair value of common stock with the assistance of an independent third-party valuation expert when issuing stock options and computing its estimated stock-based compensation expense. The assumptions underlying these valuations represented management’s best estimates, which involved inherent uncertainties and the application of significant levels of management judgment. In order to determine the fair value, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving various liquidity events; the lack of marketability of the Company’s common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions. Stock-Based Compensation Stock Options The Company recognizes stock-based compensation expense over the requisite service period on a straight-line basis. Employee and director stock-based compensation for stock options is measured based on estimated fair value as of the grant date, using the Black-Scholes option pricing model, in calculating the fair value of option grants as of the grant date. The Company uses the following assumptions for estimating fair value of option grants: Fair Value of Common Stock Expected Volatility Expected Term Risk-Free Interest Rate zero-coupon Expected Forfeiture Rate Performance-Based Options Stock-based compensation expense for performance-based options is recognized based on amortizing the fair market value as of the grant date over the periods during which the achievement of the performance is probable. Performance-based options require certain performance conditions to be achieved in order for these options to vest. These options vest on the date of achievement of the performance condition. Market-Based Options Stock-based compensation expense for market-based options is recognized on a straight-line basis over the derived service period, regardless of whether the market condition is satisfied. Market-based options subject to market-based performance targets require achievement of the performance target in order for these options to vest. The Company estimates the fair value of market-based options as of the grant date and expected term using a Monte Carlo simulation that incorporates option-pricing inputs covering the period from the grant date through the end of the derived service period. The expected volatility as of the grant date is estimated and based on the historical volatility of a group of similar companies that are publicly traded. The risk-free interest rate is based on the yield on zero-coupon Recently Issued Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12 , Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes 2019-12”). 2019-12 2019-12 2019-12 Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments Credit Losses (Topic 326): Measurements of Credit Losses on Financial Instruments 2016-13”), available-for-sale ASU 2016-13 ASU 2016-13 In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”). 2018-13 2018-13 2018-13

Inventories

Inventories	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Inventories	2. Inventories Inventories consisted of the following (in thousands): September 30, 2020 December 31, 2019 Raw materials $ 116 $ 106 Work in process 337 — Total $ 453 $ 106 As of September 30, 2020 and December 31, 2019, no finished goods were included in inventories. During the nine months ended September 30, 2020, the Company recorded a write-off	4. Inventories Inventories consisted of the following components (in thousands): December 31, 2019 2018 Raw materials $ 106 $ 98 Work in process — 841 Finished goods — — Inventories $ 106 $ 939 During the year ended December 31, 2019, the Company recorded a write-off

Property and Equipment

Property and Equipment	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Property and Equipment	3. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): September 30, 2020 December 31, 2019 Lab and manufacturing equipment $ 1,235 $ 1,231 Leasehold improvements 845 845 Office furniture and equipment 157 157 Total 2,237 2,233 Less: accumulated depreciation and amortization (1,942 ) (1,913 ) Property and equipment, net $ 295 $ 320 Depreciation and amortization expense for the three months ended September 30, 2020 and 2019 were $24,000 and $40,000, respectively. Depreciation and amortization expense for the nine months ended September 30, 2020 and 2019 was $0.1 million.	5. Property and Equipment Property and equipment consisted of the following (in thousands): Years Ended December 31, 2019 2018 Leasehold improvements $ 845 $ 840 Lab and manufacturing equipment 1,231 1,084 Office furniture and equipment 157 131 Total 2,233 2,055 Less: accumulated depreciation and amortization (1,913 ) (1,768 ) Property and equipment, net $ 320 $ 287 Depreciation and amortization expense were approximately $145 thousand and $150 thousand for the years ended December 31, 2019 and 2018, respectively.
Predecessor Company [Member]
Property and Equipment		5. Property and Equipment Property and equipment consist of the following (in thousands): December 31, 2019 2018 Furniture and fixtures $ — $ 334 Equipment — 208 Leasehold improvements — 147 — 689 Less accumulated depreciation and amortization — (535 ) Total $ — $ 154 Depreciation expense related to property and equipment was $73,000, $91,000 and $108,000 for the years ended December 31, 2019, 2018 and 2017, respectively. At December 31, 2019, the Company wrote off the remaining net book value of its property and equipment, which totaled approximately $0.1 million

Balance Sheet Details

Balance Sheet Details	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Details	4. Balance Sheet Details Prepaid and other current assets consisted of the following (in thousands): September 30, 2020 December 31, 2019 Insurance $ 466 $ — Security deposit 81 — Clinical research 13 50 Other 139 117 Total $ 699 $ 167 Other assets consisted of the following (in thousands): September 30, 2020 December 31, 2019 Insurance $ 1,016 $ — Other 75 69 Total $ 1,091 $ 69 Accrued liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Current portion of finance lease liabilities $ 8 $ 6 Compensation 272 182 Clinical trial and study related costs 161 22 Legal fees 2 169 Other 110 67 Total $ 553 $ 446 Other liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Noncurrent portion of finance lease liabilities $ 25 $ 31 Forward purchase contract 290 290 Total $ 315 $ 321	7. Balance Sheet Details Accrued liabilities consist of the following (in thousands): December 31, December 31, Current portion of notes payable – related party $ — $ 7 Accrued interest – related party — 2 Current portion of finance lease liabilities 6 25 Accrued compensation 182 86 Other 258 546 Total $ 446 $ 666 Other liabilities consist of the following (in thousands): December 31, December 31, Noncurrent portion of finance lease liabilities $ 31 $ 7 Forward purchase contract 290 290 Noncurrent portion of deferred rent — 89 Total $ 321 $ 386

Revenue

Revenue	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue	5. Revenues The following is a summary description of the material revenue arrangements, including arrangements that generated revenues during the three and nine months ended September 30, 2020 and 2019. Edge Systems License and Supply Agreement In 2014, the Company entered into a license and supply agreement (the “Edge Agreement”), amended May 17, 2018, with Edge Systems LLC (“Edge”), which was terminated in October 2019, to incorporate Histogen’s CCM skin care ingredient into Edge’s cosmetic products. The quantities to be delivered by the Company to Edge under the agreement were variable and the price per unit of CCM supplied to Edge was fixed with no variable consideration. Product returns to date have not been significant and the Company has not considered it necessary to record a reserve for product returns. The Company’s product revenues were recognized at a point in time when the underlying product was delivered to the customer which was when the customer obtained control of the product. Product revenue under this arrangement was $0.2 million and $0.4 million for the three and nine months ended September 30, 2019, respectively, and no product revenue from sales to Edge was recognized during 2020. Allergan License Agreements 2017 Allergan Amendment In 2017, the Company entered into a series of agreements (collectively, the “2017 Allergan Agreement”), which ultimately transferred Suneva Medical, Inc.’s license and supply rights of Histogen’s CCM skin care ingredient in the medical aesthetics market to Allergan Sales LLC (“Allergan”) and granted Allergan an exclusive, royalty-free, perpetual, irrevocable, non-terminable 2019 Allergan Amendment In March 2019, Histogen entered into a separate agreement with Allergan (the “2019 Allergan Amendment”) to amend the 2017 Allergan Agreement in exchange for a one-time payment and non-exclusive rights through brick-and-mortar medical and brick-and-mortar stores The Company evaluated the 2019 Allergan Amendment under ASC 606 and concluded that Allergan continues to be a customer and that the expanded license is distinct from the 2017 Allergan Agreement. The Company determined the expanded license under the 2019 Allergan Amendment to be functional intellectual property as Allergan has the right to utilize the Company’s CCM skin care ingredient, and that ingredient is functional to Allergan at the time the Company transferred the expanded license. The standalone selling price of the expanded license was not readily observable since the Company has not yet established a price for this expanded license and the expanded license has not been sold on a standalone basis to any customer. The Company accounted for the 2019 Allergan Amendment as a modification to the 2017 Allergan Agreement. The contract modification was accounted for as if the 2017 Allergan Agreement had been terminated and the new contract included the expanded license as well as the remaining performance obligations that arose from the 2017 Allergan Agreement related to the Supply of CCM to Allergan and Potential Future Improvements. The total transaction price for the new contract included the $7.5 million from the 2019 Allergan Amendment as well as the amounts deferred as of the 2019 Allergan Amendment execution date for each the Supply of CCM to Allergan and Potential Future Improvements. The standalone selling price for the Supply of CCM to Allergan was determined based on comparable sales transactions. The standalone selling price of the Potential Future Improvements was estimated at the fully burdened rate of research and development employees cost plus a commercially reasonable markup. The amount of the total transaction price allocated to the expanded license was determined using the residual approach, as a result of not having a standalone selling price for the expanded license; that is, the total transaction price less the standalone selling prices of the Supply of CCM to Allergan and Potential Future Improvements. Revenue related to the Supply of CCM to Allergan has been deferred and recognized at the point in time in which deliveries are completed while revenue related to the Potential Future Improvements has been deferred and amortized ratably over the remaining 9-year life 2020 Allergan Amendment In January 2020, the Company further amended the 2019 Allergan Amendment in exchange for a one-time payment non-exclusive The Company evaluated the 2020 Allergan Amendment under ASC 606 and concluded that Allergan continues to be a customer and that the expanded license is distinct from the 2019 Allergan Amendment. The Company determined the expanded license under the 2020 Allergan Amendment to be functional intellectual property as Allergan has the right to utilize the Company’s CCM skin care ingredient, and that ingredient is functional to Allergan at the time the Company transferred the expanded license. The standalone selling price of the expanded license was not readily observable since the Company has not yet established a price for this expanded license and the expanded license has not been sold on a standalone basis to any customer. The Company accounted for the 2020 Allergan Amendment as a modification to the 2019 Allergan Amendment (which had modified the 2017 Allergan Agreement, as noted above). The contract modification was accounted for as if the 2019 Allergan Amendment had been terminated and the new contract included the expanded license and Additional Supply of CCM to Allergan, as well as the remaining performance obligation related to Potential Future Improvements. The total transaction price for the new contract included the $1.0 million from the 2020 Allergan Amendment, the future payment for the Additional Supply of CCM to Allergan, as well as the amounts deferred as of the 2020 Allergan Amendment execution date for Potential Future Improvements. The standalone selling price for the Additional Supply of CCM to Allergan was determined using the observable inputs of historical comparable sales transactions, including the margin from such sales. The Company also considered its reduced expected cost of satisfying this performance obligation based on the current efficiencies within its CCM manufacturing processes. Due to significant efficiencies in the Company’s CCM manufacturing processes, the forecasted cost of CCM production has decreased, while the applied margin was determined by comparison to similar sales transactions in prior years. The standalone selling price of the Potential Future Improvements was estimated at the fully burdened rate of research and development employees cost plus a commercially reasonable markup. The amount of the total transaction price allocated to the expanded license was determined using the residual approach, as a result of not having a standalone selling price for the expanded license; that is, the total transaction price less the standalone selling prices of the Additional Supply of CCM to Allergan and Potential Future Improvements. Revenue related to the Additional Supply of CCM to Allergan has been deferred and will be recognized at the point in time in which deliveries are completed. Revenue related to the Additional Supply of CCM to Allergan was $0.4 million ($0.1 million of which was previously deferred), during the three and nine months ended September 30, 2020. Revenue related to the Potential Future Improvements has been deferred and amortized ratably over the remaining 9-year Remaining Performance Obligations and Deferred Revenue The remaining performance obligations are the Company’s obligations to (1) deliver Additional Supply of CCM to Allergan and (2) share with Allergan any Potential Future Improvements to CCM identified through the Company’s research and development efforts. Deferred revenue recorded for the Additional Supply of CCM to Allergan was $0.1 million and $0 as of September 30, 2020 and December 31, 2019, respectively, while deferred revenue recorded for the Potential Future Improvements was $0.1 million and $0.2 million as of September 30, 2020 and December 31, 2019, respectively. Deferred revenue is classified in current liabilities when the Company’s obligations to supply CCM or provide research for Potential Future Improvements are expected to be satisfied within twelve months of the balance sheet date. Grant Revenue In March 2017, the National Science Foundation, a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. Grant revenue recognized was $0 and $0.2 million for the three and nine months ended September 30, 2019, respectively, and no grant revenue was recognized during 2020. Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty and are nonrefundable. Professional services fees are recognized as revenue over time as the underlying services are performed. Professional services revenue related to the Company’s assistance in establishing Allergan’s alternative manufacturing facility was $0.1 million for the three months ended September 30, 2020 and 2019 and $0.3 million for the nine months ended September 30, 2020 and 2019.	10. Revenue Edge Systems License and Supply Agreement In 2014, the Company entered into a license and supply agreement (the “Edge Agreement”), amended May 17, 2018, with Edge Systems LLC (“Edge”) to incorporate Histogen’s Cell Conditioned Media (“CCM”) skin care ingredient into Edge’s cosmetic products. The quantities to be delivered by the Company to Edge under the agreement were variable and the price per unit of CCM supplied to Edge was fixed with no variable consideration. Product returns to date have not been significant and the Company has not considered it necessary to record a reserve for product returns. The Company’s product revenues are recognized at a point in time when the underlying product is delivered to the customer which is when the customer obtains control of the product. During the years ended December 31, 2019 and 2018, the Company recognized $855 thousand and $618 thousand, respectively, in product revenue under this arrangement. The Company terminated its supply agreement with Edge in October 2019 and has no further commitments under the arrangement. Allergan License Agreements In 2017, the Company entered into a series of agreements (collectively, the “2017 Allergan Agreement”) which ultimately transferred Suneva Medical, Inc.’s license and supply rights of Histogen’s CCM skin care ingredient in the medical aesthetics market to Allergan Sales LLC (“Allergan”) and granted Allergan an exclusive, royalty-free, perpetual, irrevocable, non-terminable In connection with the Company’s adoption of ASC 606, Revenue from Contracts with Customers 1. License of rights to use, manufacture and sell products containing the Company’s CCM skin care ingredient through the medical aesthetics market (Field of Use) worldwide (Territory) (“CCM License”); 2. Supply of CCM (“Supply of CCM to Allergan”); and 3. Potential future improvements made to the CCM skin care ingredients (“Potential Future Improvements”). The Company considers the CCM License as functional intellectual property as Allergan has the right to utilize the Company’s CCM skin care ingredient and that ingredient is functional to Allergan at the time the Company transferred the license. The Company determined the transaction price at inception of the Allergan License Agreement and allocated the transaction price to the various performance obligations using the standalone selling price which is comparable to the relative selling price methodology used in the original accounting treatment for the transaction. The entire amount of revenue allocated to the CCM License was recognized upon transfer of the license to Allergan in 2017. As for the Supply of CCM to Allergan, the Company initially deferred $1.8 million of revenue allocated to this performance obligation which is being recognized at the point in time in which deliveries are completed. Product revenue related to the Supply of CCM to Allergan of approximately $2.6 million and $636 thousand, including recognition of revenue from deferred revenue of $1.5 million and $292 thousand, was recognized during the years ended December 31, 2019 and 2018, respectively. Further, as of December 31, 2019 and 2018, the Company had deferred revenue related to the Supply of CCM to Allergan of $0 and $1.5 million, respectively. As for the potential future improvements to the CCM skin care ingredients, the Company initially deferred $199 thousand of revenue allocated to this performance obligation which is being recognized on a straight-line basis over a period of 123 months through the expiration of the related patents. Revenue of approximately $19 thousand was recognized during the years ended December 31, 2019 and 2018, respectively, related to the Potential Future Improvements. As of December 31, 2019 and 2018, the Company’s deferred revenue related to the Potential Future Improvements was $157 thousand and $177 thousand, respectively. The potential milestone payment was determined to be contingent on future events that are not deemed probable of occurring at this time; therefore, no revenue related to the potential milestone has been recognized or deferred in the periods presented. In March 2019, Histogen entered into a separate agreement with Allergan (the “2019 Allergan Amendment”) to further amend the 2017 Allergan Agreement in exchange for a one-time non-exclusive brick-and-mortar brick-and-mortar The Company evaluated the 2019 Allergan Amendment under ASC 606 and concluded that Allergan continues to be a customer and that the expanded license is distinct from the 2017 Allergan Agreement. The Company determined the expanded license under the 2019 Allergan Amendment to be functional intellectual property as Allergan has the right to utilize the Company’s CCM skin care ingredient, and that ingredient is functional to Allergan at the time the Company transferred the expanded license. The standalone selling price of the expanded license was not readily observable since the Company has not yet established a price for this expanded license and the expanded license has not been sold on a standalone basis to any customer. The Company accounted for the 2019 Allergan Amendment as a modification to the 2017 Allergan Agreement. The contract modification was accounted for as if the 2017 Allergan Agreement had been terminated and the new contract included the expanded license as well as the remaining performance obligations related to the Supply of CCM to Allergan and Potential Future Improvements. The total transaction price for the new contract included the $7.5 million from the 2019 Allergan Amendment as well as the amounts deferred as of the 2019 Allergan Amendment execution date for each the Supply of CCM to Allergan and Potential Future Improvements. The standalone selling price for the Supply of CCM to Allergan was determined based on comparable sales transactions to the Company’s other major customer. The standalone selling price of the Potential Future Improvements was estimated at the fully burdened rate of research and development employees cost plus a commercially reasonable markup. The amount of the total transaction price allocated to the expanded license was determined using the residual approach, as a result of not having a standalone selling price for the expanded license; that is, the total transaction price less the standalone selling prices of the Supply of CCM to Allergan and Potential Future Improvements. Revenue related to the Supply of CCM has been deferred and recognized at the point in time in which deliveries are completed while revenue related to the Potential Future Improvements has been deferred and amortized ratably over the remaining 10-year Remaining Performance Obligations and Deferred Revenue The only remaining performance obligation is the Company’s obligation to share with Allergan any Potential Future Improvements to CCM identified through the Company’s research and development efforts, for which a total of $157 thousand of deferred revenue is recorded as of December 31, 2019. Deferred revenue is classified in current liabilities when the Company’s obligations to provide research for Potential Future Improvements are expected to be satisfied within twelve months of the balance sheet date. Huapont License and Supply Agreement On September 30, 2016, concurrent with the purchase of 4,000,000 shares of Series D convertible preferred stock and 190,377 shares of common stock by Pineworld Capital Limited (or “Huapont”) on August 10, 2016, Histogen and Huapont entered into an Exclusive License and Supply Agreement (“LSA”) that had been negotiated simultaneously with and in anticipation of the closing of the Huapont investment transaction. The LSA, among other provisions, grants limited exclusive license and sublicense rights to Huapont for the commercialization and sale of HST-001 non-exclusive non-assignable HST-001 HST-001 Histogen has a right to terminate the LSA upon failure by Huapont to achieve certain diligence or sales milestones or its abandonment of commercialization of the product, certain changes of control of Huapont, Huapont’s material breach of the LSA, Huapont’s failure to purchase certain volumes of product under the LSA, or Huapont’s sale of the product outside the territory or sale of a competing product, subject to certain cure rights. Huapont may terminate the agreement if further commercialization of the product is not commercially feasible, upon Histogen’s material breach of the LSA or if Histogen sells a competing product in the territory. Huapont will indemnify Histogen for third-party claims arising from Huapont’s distribution, marketing and promotion of products in or for the territory, Huapont’s breach of the agreement or Huapont’s intentional acts or omissions or negligence. Histogen will indemnify Huapont for the development, manufacture or supply of product by or under the control of Histogen, Histogen’s breach of its obligations or warranties, intellectual property infringement in connection with the using, importing or selling of products by Huapont, infringement of trademark rights in connection with the use of Histogen’s trademarks, or Histogen’s intentional acts or omissions or negligence. Upon the adoption of ASC 606, the Company determined that as no up-front The LSA includes development milestone payments of up to $5,000,000 in aggregate; $0.8 million upon the approval of the Investigational New Drug (“IND”) by the China Food and Drug Administration (“CFDA”); $1.8 million upon the completion of all clinical trials required for a New Drug Filing (“NDA”) with the CFDA; $1.2 million upon NDA filing with the CFDA; and $1.2 million upon NDA approval by the CFDA. In accordance with ASC 606, Histogen excluded the development milestones from the transaction price as it considered such payments to be fully constrained under ASC 606 due to the inherent uncertainty in the achievement of such milestone payments, which are highly susceptible to factors outside of Histogen’s control. The Company will recognize revenue for development milestone as it becomes probable that a significant reversal in the amount of cumulative revenue recognized will not occur using the most likely method. For the years ended December 31, 2019 and 2018, the Company has not recognized any milestone revenue under the LSA. The arrangement also includes tiered royalty payments based on net sales of HST-001, Grant Revenue In March 2017, the National Science Foundation, a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange 958-605, Not-for-Profit For the years ended December 31, 2019 and 2018, the Company recognized grant revenue of $150 thousand and $300 thousand, respectively. Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable. Professional services revenue for the years ended December 31, 2019 and 2018 was $370 thousand and $204 thousand, respectively, related to the Company’s assistance in establishing Allergan’s alternative manufacturing facility.

Merger

Merger	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Merger	6. Merger The Merger, which closed on May 26, 2020, was accounted for as a reverse asset acquisition pursuant to Topic 805, Clarifying the Definition of a Business non-financial in-process The total purchase price paid in the Merger has been allocated to the net assets acquired and liabilities assumed based on their fair values as of the completion of the Merger. The following summarizes the purchase price paid in the Merger (in thousands, except share and per share amounts): Number of shares of the combined organization owned by the Company’s pre-Merger 3,394,299 Multiplied by the fair value per share of Conatus common stock (1) $ 5.56 Fair value of consideration issued to effect the Merger $ 18,872 Transaction costs 1,817 Purchase price $ 20,689 (1) Based on the last reported sale price of the Company’s common stock on the Nasdaq Capital Market on May 26, 2020, the closing date of the Merger, and gives effect to the Reverse Stock Split. The allocation of the purchase price is as follows (in thousands): Cash acquired $ 12,835 Net assets acquired 710 Acquired IPR&D (2) 7,144 Purchase price $ 20,689 (2) Represents the research and development projects of Conatus which were in-process,

PUR Settlement_Investment

PUR Settlement/Investment	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
PUR Settlement/Investment	7. PUR Settlement In April 2019, Private Histogen entered into a Settlement, Release and Termination Agreement (“PUR Settlement”) with PUR Biologics, LLC and its members which terminated the License, Supply and Operating Agreements between Private Histogen and PUR, eliminated Private Histogen’s membership interest in PUR and returned all in-process 805-50-50, Acquisition of Assets Rather than a Business As consideration for the reacquisition of the Development Assets, Private Histogen compensated PUR with both equity and cash components, including 167,323 shares of Series D convertible preferred stock with a fair value of $1.75 million and a potential cash payout of up to $6.25 million (the “Cap Amount”). Private Histogen paid PUR $0.5 million in upfront cash, forgave approximately $22,000 of accounts receivable owed by PUR to Private Histogen, and settled an outstanding payable of PUR of approximately $23,000 owed to a third-party. The Company is also obligated to make milestone and royalty payments, including (a) a $0.4 million payment upon the unconditional acceptance and approval of a New Drug Application or Pre-Market Contingencies For the acquisition of the Development Assets, Private Histogen recognized approximately $2.27 million of in-process	6. Investment in PUR As of December 31, 2018, the Company held less than a 50% interest in an investment in non-marketable In April 2019, the Company entered into a Settlement, Release and Termination Agreement with PUR and its members (“PUR Settlement”) which terminated the License, Supply and Operating Agreements between Histogen and PUR, eliminated Histogen’s membership interest in PUR and returned all in-process 805-50-50, Acquisition of Assets Rather than a Business As consideration for the reacquisition of the Development Assets, Histogen compensated PUR with both equity and cash components, including 1,166,667 shares of Series D convertible preferred stock with a fair value of $1.75 million and a potential cash payout of up to $6.25 million (the “Cap Amount”). The Company paid PUR $500 thousand in upfront cash, forgave approximately $22 thousand of accounts receivable owed by PUR to the Company, and settled an outstanding payable of PUR of approximately $23 thousand owed to a third-party. The Company is also obligated to make milestone and royalty payments, including (a) a $400 thousand upon the unconditional acceptance and approval of a New Drug Application or Pre-Market Contingencies For the acquisition of the Development Assets, the Company recognized approximately $2.27 million in research and development expense (including the cash payments of $523 thousand and Series D preferred stock issuance of $1.75 million) on the consolidated statement of operations for the year ended December 31, 2019.

Paycheck Protection Program Loa

Paycheck Protection Program Loan	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Paycheck Protection Program Loan	8. Paycheck Protection Program Loan In April 2020, Private Histogen applied for and received loan proceeds in the amount of $0.5 million (the “PPP Loan”) under the PPP as government aid for payroll, rent and utilities. The application for these funds required the Company to, in good faith, certify that the current economic uncertainty made the loan request necessary to support the ongoing operations of the Company. This certification further required the Company to take into account its current business activity and its ability to access other sources of liquidity sufficient to support ongoing operations in a manner that is not significantly detrimental to the business. The certification made by the Company did not contain any objective criteria and is subject to interpretation. Based in part on the Company’s assessment of other sources of liquidity, the uncertainty associated with future revenues created by the COVID-19 On June 5, 2020, the Paycheck Protection Program Flexibility Act was signed into law, extending the PPP Loan forgiveness period from eight weeks to 24 weeks after loan origination, extending the initial deferral period of principal and interest payments from six months to ten months after the loan forgiveness period, reducing the required amount of payroll expenditures from 75% to 60%, removing the prior ban on borrowers taking advantage of payroll tax deferral after loan forgiveness and allowing for the amendment of the maturity date on existing loans from two years to five years.

Stockholders' Equity_Deficit

Stockholders' Equity/Deficit	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Stockholders' Equity/Deficit	9. Stockholders’ Deficit Common Stock At Market Issuance Sales Agreement with Stifel, Nicolaus & Company, Incorporated Prior to the Merger, Conatus entered into an At Market Issuance Sales Agreement (the “Sales Agreement”) with Stifel, Nicolaus & Company, Incorporated (“Stifel”), pursuant to which the Conatus could sell from time to time, at its option, up to an aggregate of $35.0 million of shares of its common stock through Stifel, as sales agent. In July 2020, the Company terminated the Sales Agreement with Stifel, with no shares having been issued pursuant to the Sales Agreement. Common Stock Purchase Agreement with Lincoln Park In July 2020, the Company entered into a common stock purchase agreement (the “2020 Purchase Agreement”) with Lincoln Park which provides that, upon the terms and subject to the conditions and limitations in the 2020 Purchase Agreement, Lincoln Park is committed to purchase up to an aggregate of $10.0 million of shares of the Company’s common stock at the Company’s request from time to time during a 24 month period that began in July 2020 and at prices based on the market price of the Company’s common stock at the time of each sale. Upon execution of the 2020 Purchase Agreement, the Company sold 328,516 shares of common stock at $3.04399 per share to Lincoln Park for proceeds of $1.0 million. During the three and nine months ended September 30, 2020 the Company sold an additional 280,000 shares of common stock to Lincoln Park for net proceeds of approximately $0.3 million and as of September 30, 2020, approximately $8.5 million of common stock remains available for sale under the 2020 Purchase Agreement, subject to limitations on the amount of securities the Company may sell under its effective registration statement on Form S-3 Convertible Preferred Stock In connection with the Merger, all of the outstanding shares of Private Histogen’s convertible preferred stock were converted into 5,046,154 shares of the Company’s common stock. As of December 31, 2019, Private Histogen’s convertible preferred stock is classified as temporary equity on the accompanying condensed consolidated balance sheets in accordance with authoritative guidance for the classification and measurement of potentially redeemable securities whose redemption is based upon certain change in control events outside of Private Histogen’s control, including liquidation, sale or transfer of control of Private Histogen. Private Histogen did not adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because the occurrence of any such change of control event was not deemed probable. The authorized, issued and outstanding shares of convertible preferred stock as of December 31, 2019 consisted of the following: Shares Authorized Shares Issued and Outstanding Liquidation Preference Carrying Value (in thousands) Series A 10,000,000 1,360,547 $ 9,486 $ 9,486 Series B 35,000,000 1,144,567 7,981 9,356 Series C 8,000,000 1,075,637 7,500 5,550 Series D 20,000,000 1,465,403 15,327 14,678 Total 73,000,000 5,046,154 $ 40,294 $ 39,070 During the nine months ended September 30, 2020, the Company issued no convertible preferred stock. During the nine months ended September 30, 2019, the Company issued 16,413 shares of Series B convertible preferred stock at $6.97 per share and 216,468 shares of Series D convertible preferred stock, of which 167,323 shares related to the PUR Settlement, at $10.46 per share. General Rights and Preferences of Private Histogen Convertible Preferred Stock The holders of each series of convertible preferred stock were entitled to receive noncumulative dividends at a rate of 6% per share per annum based on the original issue price. The preferred stock dividends were payable in preference and in priority to any dividends on common stock if or when any dividends had been declared by the Board of Directors. The Company’s Board of Directors have not declared any dividends during the periods presented. The holders of the Series A, B and C convertible preferred stock were entitled to receive liquidation preferences at the rate of $6.97 per share. The Series D holders were entitled to liquidation preferences at a rate of $10.46 per share. All series holders also had a right to receive declared but unpaid dividends upon a liquidation event. The liquidation preferences to all holders of preferred stock were to have been made pari passu The shares of each series of convertible preferred stock were convertible into an equal number of shares of common stock, at the option of the holder. Likewise, at the election of the holders of the majority of the then outstanding shares of convertible preferred stock, all shares would have automatically converted to an equal number of shares of common stock. Finally, each share of preferred stock was automatically converted into common stock immediately upon the Company’s sale of its common stock in a firm commitment underwritten public offering pursuant to a registration statement under the Securities Act of 1933, as amended, resulting in the receipt by the Company of at least $20.0 million in which the per share price is at least $31.38. The conversion from the public offering would result in the convertible preferred stockholders receiving less than one common share for each of their shares being converted. The holders of each series of preferred stock were entitled to one vote for each share of common stock into which such preferred stock could then be converted; and with respect to such vote, such holders shall have full voting rights and powers equal to the voting rights and powers of the holders of common stock. Common Stock Warrants In 2016, Private Histogen issued warrants to purchase common stock as consideration for settlement of prior liability claims. The warrants for the purchase of up to 3,583 common shares at an exercise price of $23.08 a share expire on July 31, 2021. The warrants remain outstanding and unexercised for the periods presented. In addition, at September 30, 2020, warrants to purchase 1,346 shares of common stock with an exercise price of $74.30 a share remain outstanding that were issued by Conatus in connection with obtaining financing in 2016. These warrants expire on July 3, 2023. Stock-Based Compensation Equity Incentive Plans On December 18, 2017, Private Histogen established the Histogen Inc. 2017 Stock Plan (the “2017 Plan”). Under the 2017 Plan, Private Histogen was authorized to issue a maximum aggregate of 837,208 shares of common stock with adjustments for unissued or forfeited shares under the predecessor plan (the Histogen Inc. 2007 Stock Plan). In April 2019, Private Histogen amended the 2017 Plan, which increased the number of common stock available for grants by 326,711 shares. The 2017 Plan permitted the issuance of incentive stock options (“ISOs”), non-statutory In May 2020, in connection with the closing of the Merger, the Company’s stockholders approved the Company’s 2020 Incentive Award Plan (the “2020 Plan”). The maximum number of shares of the Company’s common stock available for issuance under the 2020 Plan equals the sum of (a) 850,000 shares; (b) any shares of common stock of the Company which are subject to awards under the Conatus 2013 Equity Incentive Plan (the “Conatus 2013 Plan”) as of the effective date of the 2020 Plan which become available for issuance under the 2020 Plan after such date in accordance with its terms; and (c) an annual increase on the first day of each calendar year beginning with the January 1 of the calendar year following the effectiveness of the 2020 Plan and ending with the last January 1 during the initial ten year term of the 2020 Plan, equal to the lesser of (i) five percent of the number of shares of the Company’s common stock outstanding (on an as-converted basis) Additionally, in connection with the closing of the Merger, no further awards will be made under the Conatus 2013 Plan. As of September 30, 2020, 116,091 fully vested options remain outstanding under the Conatus 2013 Plan with a weighted average exercise price of $37.59 per share. The following summarizes activity related to the Company’s stock options under the 2017 Plan and the 2020 Plan for the nine months ended September 30, 2020: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 1,362,173 $ 3.16 6.34 $ 2,926 Granted 124,119 $ 4.61 Exercised (28,684 ) $ 1.40 Cancelled or forfeited (74,576 ) $ 4.30 Outstanding at September 30, 2020 1,383,032 $ 3.26 5.87 $ 528 Vested and exercisable at September 30, 2020 897,647 $ 2.31 4.39 $ 528 Chief Executive Officer Stock Options On January 24, 2019, the Company issued 485,178 stock options to its newly appointed Chief Executive Officer. In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months. On January 28, 2020, the award agreement was amended, which became effective upon the close of the Merger in May 2020, whereby the 40% of stock options (“Liquidity Option Shares”) subject to vesting upon an initial public offering or 45 days following a change in control will now vest immediately upon meeting certain performance and market condition-based criteria. The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $200.0 million; (3) the date that the market capitalization of the Company exceeds $275.0 million, and; (4) the date that the market capitalization of the Company exceeds $300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination. On May 26, 2020, in connection with the closing of the Merger, 48,517 options of the Liquidity Option Shares became fully vested as the performance condition was achieved. For the three and nine months ended September 30, 2020, the Company recognized $20,000 and $0.1 million, respectively, in total compensation expense related to the performance and market-based options, all of which is recorded in general and administrative expense in the accompanying condensed consolidated statements of operations. As of September 30, 2020, there was $0.4 million of total unrecognized compensation cost related to unvested market condition-based options. Valuation of Stock Option Awards The following assumptions were used to calculate the fair value of awards granted to employees, non-employees Three Months Ended Nine Months Ended 2020 2019 2020 2019 Expected volatility — % 70.0 % 76.3 % 70.0 % Risk-free interest rate — % 1.59 % 0.45 % 2.54 % Expected term (in years) — 6.25 6.25 6.25 Expected dividend yield — — — — The compensation cost that has been included in the accompanying condensed consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Three Months Ended Nine Months Ended 2020 2019 2020 2019 Cost of product revenue $ (3 ) $ 9 $ 16 $ 26 Research and development 2 9 8 31 General and administrative 126 97 432 272 Total $ 125 $ 115 $ 456 $ 329 As of September 30, 2020, total unrecognized compensation cost related to unvested options, including unvested market condition-based options, was approximately $1.5 million which is expected to be recognized over a weighted-average period of 4.0 years. Common Stock Reserved for Future Issuance Common stock reserved for future issuance at September 30, 2020 is as follows: Common stock warrants 4,929 Common stock options issued and outstanding 1,499,123 Common stock available for issuance under the 2020 Plan 725,881 Total 2,229,933
Predecessor Company [Member]
Stockholders' Equity/Deficit		7. Stockholders’ Equity Common Stock In May 2017, the Company completed a public offering of 598,000 shares of its common stock at a public offering price of $55.00 per share. The shares were registered pursuant to the Company’s Registration Statement on Form S-3 filed On August 2, 2018, the Company entered into an At Market Issuance Sales Agreement (the Sales Agreement) with Stifel, Nicolaus & Company, Incorporated (Stifel), pursuant to which the Company may sell from time to time, at its option, up to an aggregate of $35.0 million of shares of its common stock through Stifel, as sales agent. Sales of the Company’s common stock made pursuant to the Sales Agreement, if any, will be made on The Nasdaq Capital Market (Nasdaq), under the Company’s Registration Statement on Form S-3 Warrants In 2013, the Company issued warrants exercisable for 1,124,026 shares of Series B preferred stock, at an exercise price of $0.90 per share, to certain existing investors in conjunction with a private placement (the 2013 Warrants) and warrants exercisable for 111,112 shares of Series B preferred stock, at an exercise price of $0.90 per share, to Oxford Finance LLC and Silicon Valley Bank in conjunction with the Company’s entry into a loan and security agreement (the Lender Warrants). Upon completion of the Company’s initial public offering (IPO), the 2013 Warrants and the Lender Warrants became exercisable for 13,623 and 1,346 shares of common stock, respectively, at an exercise price of $74.30 per share. The 2013 Warrants expired on May 30, 2018, and the Lender Warrants will expire on July 3, 2023. Stock Options The Company adopted an Equity Incentive Plan in 2006 (the 2006 Plan) under which 103,030 shares of common stock were reserved for issuance to employees, nonemployee directors and consultants of the Company. In July 2013, the Company adopted an Incentive Award Plan (the 2013 Plan), which provides for the grant of incentive stock options, nonstatutory stock options, rights to purchase restricted stock, stock appreciation rights, dividend equivalents, stock payments and restricted stock units to eligible recipients. Recipients of incentive stock options shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The maximum term of options granted under the 2013 Plan is ten years. Except for annual grants to non-employee Pursuant to the 2013 Plan, the Company’s management is authorized to grant stock options to the Company’s employees, directors and consultants. The number of shares available for future grant under the 2013 Plan will automatically increase each year by an amount equal to the least of (1) 100,000 shares of the Company’s common stock, (2) 5% of the outstanding shares of the Company’s common stock as of the last day of the Company’s immediately preceding fiscal year, or (3) such other amount as the Company’s board of directors may determine. Shares that remain available, that expire or otherwise terminate without having been exercised in full, and unvested shares that are forfeited to or repurchased by the Company under the 2006 Plan will roll into the 2013 Plan. As of December 31, 2019, a total of 395,143 options remain available for future grant under the 2013 Plan. On August 31, 2017, in connection with the appointment of its new Executive Vice President, Chief Operating Officer and Chief Financial Officer, the Company granted stock options to purchase 52,500 shares of the Company’s common stock outside of its stock option plans. The following table summarizes the Company’s stock option activity under all stock option plans for the three years ended December 31, 2019 (options in thousands): Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2016 339 $ 51.00 Granted 173 49.10 Exercised (7 ) 13.20 Forfeited/cancelled/expired (22 ) 60.90 Outstanding at December 31, 2017 483 50.50 Granted 94 50.80 Exercised (22 ) 17.10 Forfeited/cancelled/expired (16 ) 48.30 Outstanding at December 31, 2018 539 52.00 Granted 172 18.40 Exercised — — Forfeited/cancelled/expired (581 ) 45.10 Outstanding at December 31, 2019 130 $ 38.21 5.2 Exercisable at December 31, 2019 113 $ 42.91 4.5 The weighted-average fair value of options granted for the years ended December 31, 2019, 2018 and 2017 were $18.40, $39.30 and $37.90, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2019, 2018 and 2017 were $0.0 million, $0.6 million and $0.3 million, respectively. At December 31, 2019, the intrinsic value of options outstanding and exercisable were $16,000 and $1,000, respectively. Restricted Stock Units In August 2019, the Company effected a one-time one-year one-time one-year The following table summarizes the Company’s RSU activity under all equity plans for the three years ended December 31, 2019 (RSUs in thousands): Total RSUs Weighted- Grant Date Balance at December 31, 2018 — $ — Granted 160 3.10 Forfeited (15 ) 3.10 Balance at December 31, 2019 145 $ 3.10 Unrecognized compensation expense related to outstanding RSUs at December 31, 2019 was $2.1 million, which is expected to be recognized over a weighted-average vesting term of 0.6 years. Employee Stock Purchase Plan In July 2013, the Company adopted the ESPP, which permits participants to contribute up to 20% of their eligible compensation during defined rolling six-month Stock-Based Compensation The Company recorded stock-based compensation of $4.2 million, $3.8 million and $4.1 million for the years ended December 31, 2019, 2018 and 2017, respectively. Unrecognized compensation expense related to outstanding stock options at December 31, 2019 was $27,000, which is expected to be recognized over a weighted-average vesting term of 0.9 years. Common Stock Reserved for Future Issuance The following shares of common stock were reserved for future issuance at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Warrants to purchase common stock 1 1 Common stock options issued and outstanding 130 539 Common stock authorized for future option grants 395 84 RSUs outstanding 145 — Common stock authorized for the ESPP 49 50 Total 720 674

Commitments

Commitments	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Commitments	10. Commitments and Contingencies Leases In January 2020, Private Histogen entered into a long-term operating lease with San Diego Sycamore, LLC (“Sycamore”) for its headquarters that includes office and laboratory space. The lease commenced on March 1, 2020 and expires on August 31, 2031, with no options to renew or extend. The lease was accounted for as a modification of Private Histogen’s existing lease with Sycamore as the lease agreement did not grant Private Histogen an additional right-of-use The terms of the lease agreement include six months of rent abatement at lease commencement and a tenant improvement allowance of up to $2.2 million. The tenant improvements are required to be permanently affixed to the leased office and laboratory space and do not constitute leasehold improvements of the Company. During the construction period of the tenant improvements, the lease agreement requires the Company to relocate its operations to a similar Sycamore property whereby monthly rent is substantially reduced for the duration of the construction period. The lease is subject to additional variable charges for common area maintenance, insurance, taxes and other operating costs. At lease commencement, the Company recognized a right-of-use right-of-use In connection with the closing of the Merger, the Company assumed Conatus’ noncancelable operating lease agreement, as amended, for certain office space with a lease term that expired on September 30, 2020. Upon close of the Merger, the Company recognized a right-of-use sub-lease The Company leases certain office equipment that is classified as a finance lease. As of September 30, 2020, the weighted-average remaining term of the Company’s operating and finance lease was 11 years and 3.7 years, respectively. The Company recognizes right-of-use The Company does not record leases with an initial term of 12 months or less on the consolidated balance sheets. Expense for these short-term leases is recognized on a straight-line basis over the lease term. The Company has elected the practical expedient to combine lease and non-lease Future minimum payments of lease liabilities were as follows (in thousands): Operating Leases Finance Lease 2020 (remaining 3 months) $ 60 $ 3 2021 616 10 2022 757 10 2023 780 10 2024 803 5 Thereafter 6,010 — Total minimum lease payments 9,026 38 Less: imputed interest (4,277 ) (5 ) Total future minimum lease payments 4,749 33 Less: current obligations under leases — (8 ) Noncurrent lease obligations $ 4,749 $ 25 Litigation and Legal Matters The Company is subject to claims and legal proceedings that arise in the ordinary course of business. Such matters are inherently uncertain, and there can be no guarantee that the outcome of any such matter will be decided favorably to the Company or that the resolution of any such matter will not have a material adverse effect upon the Company’s consolidated financial statements. The Company does not believe that any of such pending claims and legal proceedings will have a material adverse effect on its consolidated financial statements. The Company has entered into numerous financing arrangements with Lordship Ventures Histogen Holdings LLC (“Lordship”), a related party (See Note 11). During subsequent financing events, Lordship asserted that it has certain rights and that are, in some cases, detrimental to other existing or future investors in the Company. Although the Company believes it has no further obligation to Lordship with respect to prior financing arrangements, there is no guarantee that, if requested, concessions will not be granted or that disputes will not arise with Lordship in the future.	16. Commitments and Contingencies The Company is subject to claims and legal proceedings that arise in the ordinary course of business. Such matters are inherently uncertain, and there can be no guarantee that the outcome of any such matter will be decided favorably to the Company or that the resolution of any such matter will not have a material adverse effect upon the Company’s consolidated financial statements. The Company does not believe that any of such pending claims and legal proceedings will have a material adverse effect on its consolidated financial statements. The Company has entered into numerous financing arrangements with Lordship, a related party. During subsequent financing events, Lordship asserted that it has certain rights and that are in some cases detrimental to other existing or future investors in the Company. Although the Company believes it has no further obligation to Lordship with respect to prior financing arrangements, there is no guarantee that, if requested, concessions will not be granted or that disputes will not arise with Lordship in the future.
Predecessor Company [Member]
Commitments		11. Commitments Leases The Company determines if an arrangement is a finance lease, operating lease or short-term lease at inception, or as applicable, and accounts for the arrangement under the relevant accounting literature. Currently, the Company is only party to a non-cancelable In February 2014, the Company entered into a noncancelable operating lease agreement (the Lease) for certain office space with a lease term from July 2014 through December 2019 and a renewal option for an additional five years. In May 2015, the Company entered into a first amendment to the Lease (the First Lease Amendment) for additional office space starting in September 2015 through September 2020. The First Lease Amendment also extended the term of the Lease to September 2020. The monthly base rent under the Lease and the First Lease Amendment increases approximately 3% annually from approximately $33,000 in 2015 to approximately $39,000 in 2020. In December 2019, the Company agreed to sublet the office space, in two phases, under the Lease through September 30, 2020, the reminder of the lease term. As the amounts to be received under the sublease agreement were less than the Company’s remaining payment obligations under the Lease, an impairment loss of $50,000 was recorded on the ROU asset, representing the excess of the carrying value of the ROU asset over its fair value. As of December 31, 2019, the Company’s ROU assets and liabilities related to the Lease and the First Lease Amendment are as follows (in thousands): ROU assets (included in other assets) $ 221 Current portion of lease liabilities $ 338 Total lease liabilities $ 338 The following table reconciles the undiscounted cash flows to the operating lease liabilities recorded in the balance sheet as of December 31, 2019 (in thousands): Total lease payments $ 351 Present value adjustment (13 ) Total lease liabilities $ 338 Rent expense was as follows (in thousands): Year Ended December 31, 2019 2018 2017 Operating lease $ 378 $ 378 $ 378 Short-term leases 68 27 — Total $ 446 $ 405 $ 378 Other Commitments In July 2010, the Company entered into a stock purchase agreement with Pfizer, pursuant to which the Company acquired all of the outstanding stock of Idun Pharmaceuticals, Inc., which was subsequently spun off to the Company’s stockholders in January 2013. Under the stock purchase agreement, the Company may be required to make payments to Pfizer totaling $18.0 million upon the achievement of specified regulatory milestones.

Related Parties

Related Parties	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Parties	11. Related Parties Lordship Lordship, with its predecessor entities along with its principal owner, Jonathan Jackson, have invested and been affiliated with Private Histogen since 2010. As of September 30, 2020 and December 31, 2019, Lordship controlled approximately 19% and 28% of the Company’s outstanding voting shares, respectively, and currently holds two Board of Director seats. In January 2012, Private Histogen entered into an Indemnification Agreement (the “Lordship Indemnification”) with Lordship whereby Private Histogen granted Lordship special non-dilutive one-time In November 2012, Private Histogen entered into a Strategic Relationship Success Fee Agreement with Lordship (the “Success Fee Agreement”). The Success Fee Agreement causes certain payments to be made from the Company to Lordship equal to 1% of certain product revenues and 10% of certain license and royalty revenues. The Success Fee Agreement also stipulates that if the Company engages in a merger or sale of all or substantially all (defined as 90% or more) of its assets or equity to a third party, then the Company has the option to terminate the agreement by paying Lordship the fair market value of future payments with the minimum payment being at least equal to the most recent annual payments Lordship has received. The Success Fee Agreement was amended in August 2016, but continues to carry the same rights to certain payments. Private Histogen recognized an expense to Lordship for the three months ended September 30, 2020 and 2019 of $4,000 and $2,000, respectively, and $0.1 million and $0.8 million for the nine months ended September 30, 2020 and 2019, respectively, all of which is included in general and administrative expenses on the accompanying condensed consolidated statements of operations. As of September 30, 2020 and December 31, 2019, there was a balance of $14,000 and $16,000, respectively, paid to Lordship included in other assets on the accompanying condensed consolidated balance sheet in connection with the deferral of revenue from the Allergan license transfer agreements. Promissory Notes In April 2020, the Company entered into two promissory notes (the “Notes”), each for $0.3 million, with two stockholders, one of which was a principal owner of the Company. The Notes carried a fixed return of $25,000, due upon maturity. All outstanding principal and interest were due upon the earlier of (1) June 13, 2020 or (ii) 15 days following the consummation of the Merger. In June 2020, the Notes, including principal and interest, was repaid. Dr. Stephen Chang Dr. Chang is a Board member and was acting Chief Executive Officer of the Company from April 2017 through January 2019. For the three months ended September 30, 2020 and 2019, Dr. Chang was paid $0 and $0.1 million, respectively, for consulting services and for the nine months ended September 30, 2020 and 2019, Dr. Chang was paid $15,000 and $0.1 million, respectively, for consulting services, all of which is recorded in general and administrative expenses on the accompanying condensed consolidated statements of operations.	20. Related Parties Lordship Lordship, with its predecessor entities along its principal owner, Jonathan Jackson, have invested and been affiliated with Histogen since 2010. As of December 31, 2019 and 2018, Lordship controlled approximately 28% and 29% of the voting shares (inclusive of both common and convertible preferred stock), respectively, and controlled two Board of Director seats. On November 19, 2012, the Company entered into a Strategic Relationship Success Fee Agreement with Lordship. The agreement causes certain payments to be made from the Company to Lordship equal to 1% of certain product revenues and 10% of certain license and royalty revenues. The agreement also stipulates that if the Company engages in a merger or sale of all or substantially all (defined as 90% or more) of its assets or equity to a third party, then the Company has the option to terminate the agreement by paying Lordship the fair market value of future payments with the minimum payment being at least equal to the most recent annual payments Lordship has received. This agreement was amended on August 10, 2016 but continues to carry the same rights to certain payments. The Company recognized an expense to Lordship for the years ended December 31, 2019 and 2018 of approximately $923 thousand and $41 thousand, respectively, which is included in general and administrative expenses on the consolidated statements of operations. As of December 31, 2019 and 2018, there was a balance of approximately $16 thousand and $170 thousand, respectively, paid to Lordship included in other assets on the consolidated balance sheet in connection with the deferral of revenue from the Allergan license transfer agreements. In January 2019, the Company issued 152,594 shares of common stock and 114,445 shares of Series B convertible preferred stock to Lordship, pursuant to the Indemnification Agreement, to settle its obligation (collectively, the “Lordship Indemnification”). See Note 12 – Convertible Preferred Stock for further information. During the year ended December 31, 2018, the Series B Senior Secured Convertible Notes and conventional notes held by Lordship were extinguished. Interest expense included in the consolidated statements of operations for the year ended December 31, 2018 related to the debts held by Lordship were approximately $23 thousand. Dr. Naughton Dr. Naughton is the founder and as of the periods ended held voting shares of Histogen. Dr. Naughton had served as the Chief Executive Officer and Board Chairwoman of the Company from its inception until her resignation from both positions in April 2017. At her resignation date, Dr. Naughton transitioned to the title of Founder and Chief Scientific Officer and later in 2017 added another title of Chief Business Development Officer to her roles. The Company had amounts outstanding with Dr. Naughton for deferred/unpaid compensation. On October 31, 2016, Dr. Naughton entered into a Compensation Deferral Agreement whereby a promissory note was issued by the Company for approximately $229 thousand consisting of past due compensation along with a bonus for the deferment of payment of approximately $23 thousand. During the year ended December 31, 2018, the final payment was made to extinguish the promissory note and accrued interest thereby relieving Histogen of its obligation. On November 3, 2016, the Company executed a Deferred Compensation Agreement with Dr. Naughton whereby payment of $88 thousand of her salary from October 1, 2016 to December 23, 2016 be deferred and due on July 25, 2018. As compensation for this accommodation by Dr. Naughton, an additional $10 thousand would be paid to her at the maturity date of the agreement. On March 12, 2018, the Board of Directors approved an early payment of Dr. Naughton’s compensation under the Deferred Compensation Agreement. In March 2018, the Company paid Dr. Naughton the total amount of $98 thousand due under that agreement. In addition to the above, Dr. Naughton was due unpaid compensation prior to December 31, 2015 in the amount of approximately $68 thousand. During the year ended December 31, 2018, the Company made payments totaling $68 thousand to settle the outstanding amounts due to Dr. Naughton related to the unpaid compensation prior to December 31, 2015. As of December 31, 2018, no amounts were due to Dr. Naughton related to unpaid compensation. In January 2016, Dr. Naughton advanced approximately $7 thousand to AB as an operations bridge loan. The loan calls for interest to be accrued at 10% per annum but has not been formalized. In October 2019, the Company paid Dr. Naughton the outstanding principal and accrued interest balance due under the bridge loan of approximately $9 thousand. Eileen Brandt Eileen Brandt is the daughter of Dr. Naughton and held the position of Director of Corporate Communications with Histogen through June 2019. In July 2019, Ms. Brandt resigned from her position and transitioned to a part-time consultant in a similar investor relations capacity. For the year ended December 31, 2019, Ms. Brandt was paid approximately $18 thousand. Ms. Brandt is one of the employees that had past unpaid salaries and on October 31, 2016 entered into a Compensation Deferral Agreement whereby a promissory note was issued by the Company for approximately $23 thousand consisting of the past due compensation along with a bonus for the deferment of payment of approximately $3 thousand. During the year ended December 31, 2018, the final payment was made to extinguish the promissory note and accrued interest thereby relieving Histogen of its obligation. Dr. Stephen Chang Dr. Stephen Chang is a Board member and was the acting CEO from April 2017 through January 2019. For the years ended December 31, 2019 and 2018, Dr. Chang was paid approximately $91 thousand and $132 thousand, respectively. As of December 31, 2019 and 2018, accrued payables for consulting compensation to Dr. Chang were $0 and $100 thousand, respectively. Dr. David Crean Dr. David Crean, a Board member elected to the Company’s Board of Directors in 2018, was engaged to support the Company as a consultant beginning in 2017. For the years ended December 31, 2019 and 2018, Dr. Crean was paid approximately $20 thousand and $93 thousand, respectively. The consulting agreement with Dr. Crean was not renewed for 2019. As of December 31, 2019 and 2018, accrued payables to Dr. Crean were $0 and $20 thousand, respectively. JBF Investments, Inc. JBF, along with its affiliate Clinica (formerly known as Hair Wellness, LLC, and Newco), are under one principal owner that are parties to various transactions with the Company including purchases of the Company’s common and preferred stock and licensing negotiations for HSC in the territory of Mexico. On April 30, 2018, the Company entered into an agreement with Clinica, a Mexican corporation, to license the Company’s HSC product on an exclusive basis for the nation of Mexico. In accordance with the agreement, Clinica returned the Mexico intellectual property rights to HSC along with the entire protocol package presented to the COFEPRIS to Histogen. In exchange for (i) the return of those intellectual property rights, (ii) forgiveness of a $150 thousand licensing deposit, previously recorded as a liability, and (iii) as reimbursement of the Company’s portion of costs incurred by Clinica to advance the HSC protocol package with the COFEPRIS, the Company issued JBF 341,667 shares of Series D convertible preferred stock. For the year ended December 31, 2018, the Company expensed approximately $363 thousand, which was the fair value of the Series D convertible preferred stock issued less the licensing deposit liability. Anti-Cancer Inc. Anti-Cancer Inc. (“Anti-Cancer”) is a small early stockholder of the Company who leased space to AB during 2016. Additionally, services were provided to AB by the principal owner of Anti-Cancer. As of December 31, 2019 and 2018, outstanding amounts owed to Anti-Cancer were $22 thousand and are included in the consolidated balance sheets.

Subsequent Events

Subsequent Events	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Subsequent Events	12. Subsequent Events The Company retained rights to emricasan, an orally active pan-caspase COVID-19. The Covid-19 Events subsequent to the original issuance of the condensed consolidated financial statements (unaudited) November 2020 Registered Direct Offering In November 2020, we entered into a securities purchase agreement with several institutional and accredited investors for the sale by us of 2,522,784 shares of our common stock at a purchase price of $1.78375 per share, in a registered direct offering, with H.C. Wainwright & Co., LLC acting as placement agent. Concurrently with the sale of the shares, we also sold unregistered warrants to purchase up to an aggregate of 1,892,088 shares of common stock. The gross proceeds from this offering were $4.5 million.	21. Subsequent Events The Company has evaluated subsequent events through March 11, 2020, the date these consolidated financial statements were available to be issued. Proposed Merger with Conatus In January 2020, the Company entered into the Merger Agreement with Conatus Pharmaceuticals, Inc. and Merger Sub. Pursuant to the Merger Agreement, Merger Sub will be merged with and into Histogen, with Histogen continuing as a wholly-owned subsidiary of Conatus and the surviving corporation of the merger. See Note 1 – Organization and Nature of Operations for further information. Allergan Amendment On January 17, 2020, the Company and Allergan amended the Allergan Agreements, further clarifying the fields of use, the product definition and rights to certain improvements, as well as the Company agreeing to supply additional CCM in 2020 and provide further technical assistance to Allergan (the cost of which shall be reimbursed to Histogen), for a one-time Office Lease In January 2020, the Company entered into a long-term lease agreement with San Diego Sycamore, LLC for office and laboratory space. The new lease commenced on March 1, 2020 and expires on August 31, 2031, with no options to renew or extend. Base rent is equal to $59,775 per month at commencement and increases at a fixed rate over the term of the lease. In addition to monthly base rent, the Company is obligated to pay certain customary amounts for its share of operating expenses and utilities. The lease agreement includes six months of rent abatement and a tenant improvement allowance for renovations. U.S. Department of Defense Grant Award In February 2020, the Company received a grant award recommendation from the U.S. Department of Defense (“DoD”) to fund the development of one of its novel clinical assets. As part of the award process, the Company is required to submit additional documentation, including a proposed budget, prior to receiving funding. The Company is in the process of negotiating the specific terms of the award and completing the additional documentation required for submission to the DoD.
Predecessor Company [Member]
Subsequent Events		14. Subsequent Events On January 28, 2020, Conatus, Merger Sub, and Histogen, entered into a Merger Agreement, pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Histogen, with Histogen continuing as Conatus’ wholly owned subsidiary and the surviving corporation of the merger. Consummation of the merger is subject to certain closing conditions, including, among other things, approval by Conatus’ and Histogen’s stockholders. Should the Merger Agreement be terminated prior to consummation, the Merger Agreement contains certain termination rights for both Conatus and Histogen, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $500,000, and in some circumstances reimburse the other party’s expenses up to a maximum of $350,000.

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Organization and Basis of Presentation	1. Organization and Nature of Operations Histogen, Inc. (“Histogen” or the “Company”) is a regenerative medicine company established as a Delaware Corporation in November 2007. The Company is focused on developing innovative products for aesthetic and therapeutic applications based upon the Company’s unique technology that utilizes proteins and growth factors produced by hypoxia-induced multipotent cells. Histogen has a rich portfolio of products derived from one core technology process that fulfills market needs without using embryonic stem cells or animal components. The Company’s products are all covered by patented technologies which focus on replacing and regenerating tissues in the body. The Company’s lead drug candidate is a hair stimulating complex (“HSC”) intended to be a physician-administered therapeutic for alopecia (hair loss). Phase 1 and Phase 1/2 clinical trials of HSC have been completed outside the United States, with results that produced significant efficacy and a clear safety profile and margin. A Phase 1 clinical trial of HSC in the United States under a Federal Drug Administration (“FDA”) approved Investigational New Drug (“IND”) has been completed and reports filed with the FDA in 2019. In 2019, the Company established HST-001 HST-002 HST-003 non-prescription The Company is subject to risks common to other life science companies in the early development stage including, but not limited to, uncertainty of product development and commercialization, lack of marketing and sales history, development by its competitors of new technological innovations, dependence on key personnel, market acceptance of products, product liability, protection of proprietary technology, ability to raise additional financing, and compliance with the Food and Drug Administration and other government regulations. If the Company does not successfully advance its technologies into and through human clinical trials, form partnerships for its programs or license-out Proposed Merger with Conatus On January 28, 2020, Histogen entered into the Merger Agreement with Conatus Pharmaceuticals, Inc. (“Conatus”) and Merger Sub. Pursuant to the Merger Agreement, Merger Sub will be merged with and into Histogen, with Histogen continuing as a wholly-owned subsidiary of Conatus and the surviving corporation of the merger. The merger is expected to be accounted for as a reverse asset acquisition in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Histogen will be deemed to be the accounting acquirer for financial reporting purposes. This determination is supported based on the expectations that, immediately following the merger: (i) Histogen stockholders will own a substantial majority of the voting rights of the combined organization; (ii) Histogen will designate a majority (six of eight) of the initial members of the board of directors of the combined organization; and (iii) Histogen’s senior management will hold all key positions in senior management of the combined organization and no employees will be retained from Conatus. The merger is expected to be accounted for as a reverse asset acquisition as the fair value of the acquired preclinical assets is deemed to be substantially concentrated in a group of similar assets that do not meet the definition of a business. Accordingly, for accounting purposes: (i) the merger will be treated as the equivalent of Histogen issuing stock to acquire the net assets of Conatus, (ii) the net assets of Conatus will be recorded based upon the fair values in the financial statements at the time of closing, (iii) the reported historical operating results of the combined company prior to the merger will be those of Histogen and (iv) for periods prior to the merger, shareholders’ equity of the combined company is presented based on the historical equity structure of Conatus. Consummation of the Merger is subject to certain closing conditions, including, among other things, approval by Histogen’s and Conatus’ stockholders. Should the Merger Agreement be terminated prior to consummation, the Merger Agreement contains certain termination rights for both Histogen and Conatus, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $500,000, and in some circumstances reimburse the other party’s expenses up to a maximum of $350,000. Under the terms of the Merger Agreement, all of the Company’s outstanding common and preferred stock will be exchanged for common stock of Conatus and all outstanding options exercisable for common stock and warrants of the Company will be exchanged for options and warrants exercisable for common stock of Conatus.
Predecessor Company [Member]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Conatus Pharmaceuticals Inc. (the Company) was incorporated in the state of Delaware on July 13, 2005. The Company is a biotechnology company that has been focused on the development and commercialization of novel medicines to treat chronic diseases with significant unmet need. In December 2016, the Company entered into an Option, Collaboration and License Agreement (the Collaboration Agreement) with Novartis Pharma AG (Novartis) for the development and commercialization of emricasan, an orally active pan-caspase In March 2019, the Company announced that top-line ENCORE-NF top-line ENCORE-LF 24-week ENCORE-PH 24-week Consequently, the Company and Novartis have no further development plans for emricasan, and the Company and Novartis entered into an amendment to the Collaboration Agreement, pursuant to which the Company and Novartis mutually agreed to terminate the Collaboration Agreement, effective September 30, 2019. In order to extend the Company’s resources, the Company commenced a restructuring plan in June 2019 that included reducing staff and suspending development of its inflammasome disease candidate, CTS-2090, As of December 31, 2019, the Company has devoted substantially all of its efforts to product development and has not realized product sales revenues from its planned principal operations. The Company has a limited operating history, and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses since its inception and, as of December 31, 2019, had an accumulated deficit of $198.0 million. The Company expects to continue to incur net losses for at least the next several years. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. As of December 31, 2019, the Company had cash and cash equivalents of $20.7 million and working capital of $20.0 million. Based on the Company’s current business plan, management believes that its existing cash and cash equivalents will be sufficient to fund the Company‘s obligations for at least twelve months from the issuance date of these financial statements. If the Company is unable to generate revenues adequate to support its cost structure, the Company may need to raise additional equity or debt financing or seek to complete one of the strategic alternatives described above. Reverse Stock Split On May 26, 2020, in connection with, and prior to the completion of, the Merger with Histogen discussed above, the Company effected a reverse stock split of the Company’s common stock at a ratio of one-for-ten (the

Liquidity and Going Concern

Liquidity and Going Concern	12 Months Ended
	Dec. 31, 2019
Text Block [Abstract]
Liquidity and Going Concern	2. Liquidity and Going Concern From inception the Company has accumulated losses of $43.9 million and expects to incur operating losses and generate negative cash flows from operations for the foreseeable future. As of December 31, 2019, the Company had $2.1 million in cash and cash equivalents, which is not sufficient to sustain its operations through the second quarter of 2020. The Company has not yet established ongoing sources of revenues sufficient to cover its operating costs and will need to continue to raise additional capital to support its future operating activities, including progression of its development programs, preparation for commercialization, and other operating costs. Management’s plans with regard to these matters include entering into a combination of additional debt or equity financing arrangements, government funding, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. There can be no assurance that the Company will be able to obtain additional financing on terms acceptable to the Company, on a timely basis or at all. Additionally, as stated in Note 1 – Organization and Nature of Operations, the Company has entered into a Merger Agreement with Conatus that, if consummated, will provide capital to support the Company’s operating activities beyond the second quarter of 2020. However, additional funding will be required for the Company to sustain operations beyond twelve months from the date the consolidated financial statements were available to be issued as the Company expects an increase in cash outflows as compared to its historical spend for its planned clinical trial activities over the next twelve months. The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. Based on the above, there is substantial doubt about the Company’s ability to continue as a going concern within one year from the date the consolidated financial statements are available to be issued. The consolidated financial statements do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies	3. Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The consolidated financial statements include the accounts of the Company and its controlled subsidiaries and have been prepared in accordance with U.S. GAAP. All intercompany balances and transactions have been eliminated upon consolidation. The Company acquired Centro De Investigacion de Medicina Regenerativa, S.A. de C.V. (“CIMRESA”), a company in Mexico, during 2018 to facilitate a potential clinical development program for HSC. This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to FDA). CIMRESA has no operational or financial activity for the years ended December 31, 2019 and 2018. The Company holds an interest in Adaptive Biologix, Inc. (“AB”, formerly Histogen Oncology, LLC). AB was formed to develop and market applications for the treatment of cancer. The Company consolidates AB into its consolidated financial statements. Joint Venture and Variable Interest Entities The Company determined that AB is a variable interest entity (“VIE”) and that Histogen is its primary beneficiary. The Company holds greater than 50% of the shares and has the authority to manage the business and affairs of the VIE. AB’s other shareholder does not have a controlling interest. On January 12, 2018, AB was converted into a traditional C corporation, a Delaware corporation, under a Plan of Conversion agreement between the Company and the other member of the limited liability company, Wylde, LLC (“Wylde”). The entity structure change eliminated some of the special rights Wylde had under the LLC charter and gave the Company more control over the voting rights under the new corporate structure. The Plan of Conversion called for 3,800,000 common stock shares of AB to be issued to the Company and Wylde in proportion to their interest in the LLC immediately before the agreement was executed. Contemporaneously, the Company offered to purchase, and Wylde agreed to sell, 100,000 of the AB common shares for $1.00 per share for a total price of $100 thousand. The completion of this transaction among the stockholders of AB resulted in Histogen owning 2,600,000 common shares or approximately 68%. A VIE is typically an entity for which the Company has less than a 100% equity interest but controls the decision making over the business and affairs of the entity, directs the decisions driving the economic performance of such entity and participates in the profit and losses of such an entity. The Company weighed both quantitative and qualitative information about the different risks and reward characteristics of each entity and the significance of that entity to the consolidating group in the aggregate. Reclassifications Certain prior period amounts have been reclassified to conform to the current period presentation. These reclassifications had no effect on previously reported net loss, Stockholders’ deficit or cash flows from operating activities. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the years presented. Management believes that these estimates and assumptions are reasonable, however, actual results may differ and could have a material effect on future results of operations and financial position. Significant estimates and assumptions include the allowance for doubtful accounts, useful lives of property and equipment, unrecognized tax benefits, potential reserves for excess or obsolete inventory, the fair value of warrant and indemnification liabilities, the fair value of the Company’s common stock, stock-based compensation, and best estimate of selling price of revenue deliverables. Actual results may materially differ from those estimates. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with an original maturity date of ninety days or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking, money market accounts and brokerage accounts. Restricted cash consists of cash held as collateral for the issuer of its credit card accounts. Concentrations Credit Risk The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institutions in which those deposits are held. Customer Risk For the years ended December 31, 2019 and 2018, one customer accounted for revenues of approximately $10.5 million, or 91% of total revenue, and $860 thousand, or 48% of total revenue, respectively. The accounts receivable balance of the customer was approximately $11 thousand and $21 thousand as of December 31, 2019 and 2018, respectively. Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. The allowance is based on an analysis of historical bad debt, current receivables aging and expected future write-offs of uncollectible accounts, as well as an assessment of specific identifiable accounts considered at risk or uncollectible. Additions to the allowance for doubtful accounts include provisions for bad debt and deductions from the allowance for doubtful accounts include customer write-offs. Allowance for doubtful accounts was $0 and approximately $22 thousand as of December 31, 2019 and 2018, respectively. Inventories Inventories, consisting of raw materials, work in process, and finished goods, are valued at the lower of cost (first-in, first-out Property and Equipment Property and equipment are reported net of accumulated depreciation and amortization and are comprised of office furniture and equipment, lab and manufacturing equipment, and leasehold improvements. Ordinary maintenance and repairs are charged to expense, while expenditures that extend the physical or economic life of the assets are capitalized. Furniture and all equipment are depreciated over their estimated economic lives, or five years, using the straight-line method. Leasehold improvements are amortized over their estimated useful lives and limited by the remaining term of the building lease, using the straight-line method. Valuation of Long-Lived Assets Long-lived assets to be held and used, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. The Company has not recognized any impairment to long-lived assets through December 31, 2019. Warrant Liabilities for Convertible Preferred Stock The Company accounts for freestanding warrant instruments that either conditionally or unconditionally obligate the issuer to transfer redeemable stock as liabilities regardless of the timing of the redemption feature or price, even though the underlying shares may be classified as permanent or temporary equity. Since the Company’s convertible preferred stock is contingently redeemable, the warrants to purchase shares of convertible preferred stock are accounted for as liabilities. The Company estimates the fair values of the warrants using the Black-Scholes option pricing model. The liabilities for warrants to purchase the convertible preferred stock is remeasured at each balance sheet date with changes to fair value being recognized as a component of other income (expense) in the consolidated statements of operations. As of December 31, 2019, the warrant liabilities for convertible preferred stock expired unexercised and are no longer outstanding. Indemnification Liability The Company estimates the fair value of the indemnification liability using the fair value of the Series B preferred stock and the estimated fair value of the Company’s common stock price at the end of each period. Any resulting increase or decrease in estimated fair value is recorded as a component of other income (expense) in the consolidated statements of operations. In January 2019, the indemnification liability was settled. See Note 20 – Related Parties for further information. Fair Value Measurements ASC 820, Fair Value Measurements • Level 1 — Observable inputs such as quoted price (unadjusted) for identical instruments in active markets. • Level 2 — Observable inputs such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model derived valuations whose significant inputs are observable. • Level 3 — Unobservable inputs that reflect the reporting entity’s own assumptions. As of December 31, 2019, the Company did not have any assets or liabilities measured at fair value on its consolidated balance sheet. The following table presents the Company’s fair value hierarchy for its liabilities measured at fair value as of December 31, 2018 (in thousands): Fair Value Measurements at December 31, Quoted Prices Significant Other Significant Indemnification liability $ 239 $ — $ — $ 239 Warrant liabilities 276 — — 276 Total fair value $ 515 $ — $ — $ 515 The change in the liabilities measured at fair value using Level 3 unobservable inputs is as follows (in thousands): Indemnification Warrant Balance at December 31, 2017 $ — $ 229 Issuance 182 — Change in fair value 57 47 Balance at December 31, 2018 $ 239 $ 276 Change in fair value — (276 ) Settlement (239 ) — Balance at December 31, 2019 $ — $ — The following inputs were used in determining the fair value of the indemnification and warrant liabilities valued using the Black-Scholes-Merton option pricing model: December 31, 2018 Expected volatility 59.0 % Risk-free interest rate 2.6 % Expected term (in years) 1.0 Expected dividend yield 0.0 % Convertible Preferred Stock Convertible preferred stock subject to mandatory redemption is classified as a liability and measured at fair value and is included as a component of other liabilities in the accompanying consolidated balance sheets. See Note 11 – Forward Purchase Contract for further information. Convertible preferred stock that is conditionally redeemable (including preferred stock that has redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) is classified as temporary equity. Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the consolidated financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner Revenue Recognition Product and License Revenue The Company records revenue in accordance with ASC 606, Revenue from Contracts with Customers Grant Revenue In March 2017, the National Science Foundation (“NSF”), a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange 958-605, Not-for-Profit Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable. Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition, including write-offs of inventory. Cost of Professional Services Revenue Cost of professional services revenue represents the Company’s costs for full-time employee equivalents (“FTE”) and actual out-of-pocket Research and Development Expenses All research and development costs are charged to expense as incurred. Research and development expenses primarily include (i) payroll and related costs associated with research and development performed, (ii) costs related to clinical and preclinical testing of the Company’s technologies under development, and (iii) other research and development including allocations of facility costs. Acquired In-Process The Company has acquired and may continue to acquire the rights to drug candidates in various stages of development. The up-front in-process Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying consolidated statements of operations. General and Administrative Expenses General and administrative expenses represent personnel costs for employees involved in general corporate functions, including finance, accounting, legal and human resources, among others. Additional costs included in general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, charitable contributions, recruiting, allocated facility and general information technology costs, depreciation and amortization, and other general corporate overhead expenses. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income taxes are recorded for temporary differences between consolidated financial statement carrying amounts and the tax basis of assets and liabilities. Deferred tax assets and liabilities reflect the tax rates expected to be in effect for the years in which the differences are expected to reverse. A valuation allowance is provided if it is more likely than not that some or all the deferred tax assets will not be realized. The Company also follows the provisions of accounting for uncertainty in income taxes which prescribes a model for the recognition and measurement of a tax position taken or expected to be taken in a tax return, and provides guidance on derecognition, classification, interest and penalties, disclosure and transition. The Company’s policy is to recognize interest or penalties related to income tax matters in income tax expense. Interest and penalties related to income tax matters were not material for the periods presented. Net Loss Per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. The calculation for net loss per share gives effect to the dilutive securities under the treasury stock method. For the years ended December 31, 2019 and 2018, there is no difference in the number of shares used to compute basic and diluted net loss per share due to the Company’s net loss position. The following table sets forth potentially dilutive shares that have been excluded from the calculation of net loss per share because of their anti-dilutive effect: Years Ended December 31, 2019 2018 Common stock options issued and outstanding 9,497,923 6,150,000 Shares issuable upon conversion of convertible preferred stock 35,184,882 33,561,102 Warrants to purchase common stock 25,000 25,000 Warrants to purchase convertible preferred stock — 950,000 Total anti-dilutive shares 44,707,805 40,686,102 Common Stock Valuations The Company is required to periodically estimate the fair value of common stock when issuing stock options and computing its estimated stock-based compensation expense. The fair value of common stock was determined on a periodic basis, with the assistance of an independent third-party valuation expert. The assumptions underlying these valuations represented management’s best estimates, which involved inherent uncertainties and the application of significant levels of management judgment. The fair value of the common stock underlying the Company’s stock options was estimated at each grant date. The Company’s Board of Directors intended all options granted to be exercisable at a price per share not less than the estimated per share fair value of common stock underlying those options on the date of grant. In order to determine the fair value, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving a liquidity event, such as an initial public offering, or IPO, or sale, given prevailing market conditions; the lack of marketability of the Company’s common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions. Stock-Based Compensation Pursuant to ASC 718, Stock Compensation, The Company estimates the fair value of stock option awards to employees, directors and non-employees non-employee zero-coupon Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. In June 2016, the FASB issued ASU 2016-13, Financial Instruments Credit Losses (Topic 326): Measurements of Credit Losses on Financial Instruments available-for-sale 2016-13 In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value non-public 2018-13 In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In January 2020, the FASB issued ASU 2020-01, Investments – Equity Securities (Topic 321), Investments – Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) – Clarifying the Interactions between Topic 321, Topic 323, and Topic 815 (a consensus of the Emerging Issues Task Force) Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Leases 2018-11, Leases (Topic 842): Targeted Improvements 2016-02 use-of-hindsight
Predecessor Company [Member]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash. Additionally, the Company established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Marketable Securities The Company classifies its marketable securities as available-for-sale At each balance sheet date, the Company assesses available-for-sale Fair Value of Financial Instruments The carrying amounts of collaboration receivables, prepaid and other current assets, and accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items. Property and Equipment Property and equipment, which consisted of furniture and fixtures, computers and office equipment, scientific equipment and leasehold improvements, were stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements were amortized over the shorter of their estimated useful lives or the lease term. Long-Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objective. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset’s fair value. Through December 31, 2019, the Company has recognized $50,000 in impairment losses. Revenue Recognition Under the relevant accounting literature, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. The Company performs the following five steps in order to determine revenue recognition for contracts: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, the entity satisfies a performance obligation. At contract inception, the Company identifies the performance obligations in the contract by assessing whether the goods or services promised within each contract are distinct. Revenue is then recognized for the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. In a contract with multiple performance obligations, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation, which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price(s) may include estimates regarding forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. Any change made to estimated progress towards completion of a performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in a contract, the Company recognizes revenues from the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from the allocated transaction price. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue or expense recognition as a change in estimate. At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being reached. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or a collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates catch-up For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, and a license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, the Company has not recognized any royalty revenue from collaborative arrangements. In December 2016, the Company entered into an Option, Collaboration and License Agreement (the Collaboration Agreement) and an Investment Agreement (the Investment Agreement) with Novartis Pharma AG (Novartis). The Company concluded that there were two significant performance obligations under the Collaboration Agreement: the license and the research and development services, but that the license is not distinct from the research and development services as Novartis cannot obtain value from the license without the research and development services, which the Company is uniquely able to perform. The Company concluded that progress towards completion of the performance obligations related to the Collaboration Agreement is best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The Company periodically reviews and updates the estimated collaboration expenses, when appropriate, which adjusts the percentage of revenue that is recognized for the period. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in the period could be materially impacted. The transaction price to be recognized as revenue under the Collaboration Agreement consists of the upfront payment, option exercise fee, deemed revenue from the premium paid by Novartis under the Investment Agreement and estimated reimbursable research and development costs. Certain expenses directly related to execution of the Collaboration Agreement were capitalized as assets on the balance sheet and are being expensed in a manner consistent with the methodology used for recognizing revenue. The Collaboration Agreement was terminated, effective September 30, 2019, and the Company will not receive any future milestone, royalty or profit and loss sharing payments under the Collaboration Agreement. See Note 9 – Collaboration and License Agreements for further information. Research and Development Expenses All research and development costs are expensed as incurred. Income Taxes The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. As of December 31, 2019, there are no unrecognized tax benefits included in the balance sheet that would, if recognized, affect the Company’s effective tax rate. The Company has not recognized interest and penalties in the balance sheets or statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2019, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities. Stock-Based Compensation Stock-based compensation expense for stock option grants and restricted stock units (RSUs) under the Company’s equity plans is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period of the stock-based award, and forfeitures are recognized as they occur. Stock-based compensation expense for employee stock purchases under the Company’s 2013 Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month The fair value of stock options is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method. The expected volatility of stock options is based upon the historical volatility of the Company and a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2019 2018 2017 Assumptions Risk-free interest rate 1.82% - 2.50 % 2.55% - 3.03 % 1.83% - 2.13 % Expected dividend yield 0 % 0 % 0 % Expected volatility 105% - 119 % 94% - 100 % 93% - 97 % Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1 Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from nonowner sources, including unrealized gains and losses on marketable securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is used in making decisions regarding resource allocation and assessing performance. To date, the Company has viewed its operations and managed its business as one segment operating primarily in the United States. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common share equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities have been excluded from the computation of diluted net loss per share in the periods in which they would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to compute basic and diluted shares outstanding due to the Company’s net loss position. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in thousands): December 31, 2019 2018 2017 Warrants to purchase common stock 1 1 15 Common stock options issued and outstanding 130 539 482 RSUs outstanding 145 — — Shares issuable upon conversion of convertible note payable — — 296 Total 276 540 793 Recent Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, 2016-02 right-of-use 2016-02, non-lease See Note 11 – Commitments for further information.

Notes Payable - Related Parties

Notes Payable - Related Parties	12 Months Ended
	Dec. 31, 2019
Text Block [Abstract]
Notes Payable - Related Parties	8. Notes Payable – Related Parties Lordship On December 7, 2015, Lordship Ventures Histogen Holdings LLC (“Lordship”) made a $25 thousand advance to the Company that was later formalized into a note on February 15, 2016. Additional advances made by Lordship in early 2016 in the amounts of $25 thousand and $50 thousand were formalized into notes dated March 20, 2016 and April 21, 2016, respectively. The Lordship notes carried an interest rate of 10% per annum and both the principal and accrued interest were due the earlier of (i) the completion by Histogen of a transaction in which it raises a minimum of $3 million of equity capital or (ii) December 31, 2017. In connection with the notes, the Company also issued warrants on February 15, 2016, March 20, 2016 and April 21, 2016 to Lordship for the right to purchase 50,000, 50,000 and 100,000 shares of Series D convertible preferred stock, respectively, as additional consideration. The strike price of all three Lordship warrants were at $1.50 per share and expired unexercised on December 31, 2018. Since the Lordship warrants were issued in conjunction with the Lordship notes, the value of the warrants creates a discount against the face value amounts of the notes. The fair value of the warrants was determined to be approximately $4 thousand for the February 15 warrants, approximately $5 thousand for the March 20 warrants and approximately $10 thousand for the April 21 warrants, respectively, using the Black-Scholes option pricing model. The discounts on the carrying value of the notes have been amortized over the life of each of the notes using the effective interest method. On August 10, 2016, in conjunction with the Huapont investment transaction, the Lordship notes were modified through the Conversion, Termination and Release Agreement (“CTRA”) as of that date. The CTRA called for the extension of the due date of the two remaining outstanding Lordship notes to July 25, 2018. With these modifications it was determined that the present value of the cash flows of the original Lordship notes had changed by more than 10% and in accordance with ASC 470, Debt, was treated as an early extinguishment of the notes as of August 10, 2016. During the year ended December 31, 2018, the final payment was made to extinguish the notes and accrued interest thereby relieving Histogen of its obligation. Employees On January 14, 2016, Dr. Naughton advanced approximately $7 thousand to AB as an operations bridge loan. The loan calls for interest to be accrued at 10% per annum but has not been formalized. During the year ended December 31, 2019, the final payment was made to extinguish the note payable to Dr. Naughton thereby relieving Histogen of its obligation. The Company had amounts outstanding with various employees for deferred compensation. On October 31, 2016 certain employees, including Dr. Naughton, entered into compensation deferral agreements whereby employee promissory notes were issued by the Company for the outstanding amounts as of that date. These notes called for simple interest to accrue as of October 31, 2016 at 5% per annum with a due date of December 31, 2018. During the year ended December 31, 2018, the final payment was made to extinguish the promissory notes and accrued interest thereby relieving the Company of its obligation. Series B Convertible Notes The Company entered into Series B Senior Secured Convertible Notes payable on demand between May 19 and December 13, 2012 (the “period”). Over the course of this period, in tranches ranging from $11 thousand to $400 thousand, Lordship advanced approximately $2.6 million with a 10% interest rate per annum, convertible into Series B convertible preferred stock at $1.00 per share at the option of the holder. In a later agreement dated November 19, 2012, each of the smaller notes were swept up into a larger omnibus note totaling approximately $2.6 million. These notes were secured by the patent and intellectual property portfolios of the Company. On August 10, 2016, in connection with the Huapont investment transaction through the CTRA, the “on demand” terms were changed to a due date of February 1, 2018. On February 1, 2018, pursuant to the First Amendment to the CTRA, the Company and Lordship agreed to have their Series B Senior Secured Convertible Notes outstanding converted into Series B convertible preferred stock at $1.00 per share. Under this amendment, the definition of the trigger amount was changed, for which a $375 thousand payment was made to Lordship. The payment was classified as an inducement expense as a component of other income (expense) in the consolidated statements of operations. Pursuant to the change of the definition, the Series B Senior Secured Convertible Notes were converted to Series B convertible preferred stock, all accumulated accrued interest as of February 1, 2018 of approximately $1.4 million was forgiven, and the lien on the Company’s patent and intellectual property portfolios securing the notes was removed. The principal and the interest forgiven were recognized as a capital contribution upon conversion.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	9. Leases As described above in Note 3 – Recently Adopted Accounting Pronouncements, the Company adopted Topic 842 as of January 1, 2019. Prior period amounts have not been adjusted and continue to be reported in accordance with the Company’s historic accounting under Topic 840. The Company leases office space and office equipment which are classified as an operating lease and finance lease, respectively. The office space lease is subject to additional variable charges for common area maintenance and other variable costs. As of December 31, 2019, the weighted-average remaining term of the Company’s operating and finance leases was 0.2 years and 4.5 years, respectively. Right-of-use right-of-use The Company’s office space includes an option to extend the lease for one five-year term. This option was not included in the determination of the right-of-use The Company does not record leases with an initial term of 12 months or less on the balance sheet. Expense for these short-term leases is recognized on a straight-line basis over the lease term. The Company has elected the practical expedient to combine lease and nonlease components into a single component for all classes of underlying assets. The Company’s lease assets and lease liabilities were as follows (in thousands): Balance Sheet Classification December 31, Assets Operating lease Right-of-use $ 95 Finance leases Property and equipment, net 37 Total lease assets $ 132 Liabilities Current Operating lease liability Current portion of lease liability $ 108 Finance lease liabilities Accrued liabilities 6 Total current liabilities 114 Noncurrent Operating lease liability Noncurrent portion of lease liability — Finance lease liabilities Other liabilities 31 Total noncurrent liabilities 31 Total lease liabilities $ 145 The components of lease expense were as follows (in thousands): Statement of Operations Classification Operating lease cost: Cost of product revenue $ 165 Research and development 245 General and administrative 160 Total operating lease cost 570 Finance lease cost: Amortization of right-of-use Property and equipment, net 25 Interest on lease liabilities Interest expense 5 Total finance lease cost 30 Future minimum payments of lease liabilities were as follows (in thousands): Operating Lease Finance Leases 2020 $ 108 $ 10 2021 — 10 2022 — 10 2023 — 10 2024 — 6 Total minimum lease payments 108 46 Less: imputed interest — (9 ) Total future minimum lease payments 108 37 Less: current obligations under leases (108 ) (6 ) Noncurrent lease obligations $ — $ 31 Supplemental cash flow information related to leases were as follows (in thousands): Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating lease $ 570 Operating cash flows from finance leases 5 Financing cash flows from finance leases 25 Right-of-use 619 Right-of-use $ 40

Forward Purchase Contract

Forward Purchase Contract	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Forward Purchase Contract	11. Forward Purchase Contract In late 2011, Histogen contracted for research services from EPS Global Research Pte. Ltd. (“EPS”) to conduct clinical trials and compile data from a study in the Philippines of its HSC predecessor that took place in 2011 and 2013. The unpaid amount due for the services was approximately $340 thousand. On January 26, 2017, Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby the Company paid $50 thousand and issued EPS 100,000 shares of Series D convertible preferred stock. The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $290 thousand, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. Histogen has the sole option to initiate the timing of the repurchase of the shares before the deadline date. The Settlement Agreement was treated as debt subject to ASC 470 and a repurchase commitment under ASC 480, Distinguishing Liabilities from Equity The Company determined the fair value of the liability to be approximately $290 thousand which is the value as if the repurchase commitment was exercised immediately. As of December 31, 2019 and 2018, the fair value of the EPS forward contract remained at approximately $290 thousand and is included as a component of other liabilities in the accompanying consolidated balance sheets.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2019
Convertible Preferred Stock [Member]
Convertible Preferred Stock	12. Convertible Preferred Stock Presentation The convertible preferred stock instruments are contingently redeemable preferred stock. Each series contains the same redemption features upon a liquidation event that places the stockholder ahead of and in preference to the common stockholders of the Company. The convertible preferred stock is presented on the consolidated balance sheets as temporary equity. The authorized, issued and outstanding shares of convertible preferred stock as of December 31, 2019 consist of the following: Shared Shares Issued and Liquidation Carrying (in thousands) Series A 10,000,000 9,486,575 $ 9,486 $ 9,486 Series B 35,000,000 7,980,620 7,981 9,356 Series C 8,000,000 7,500,000 7,500 5,550 Series D 20,000,000 10,217,687 15,327 14,678 Total 73,000,000 35,184,882 $ 40,294 $ 39,070 The authorized, issued and outstanding shares of convertible preferred stock as of December 31, 2018 consist of the following: Shared Shares Issued and Liquidation Carrying (in thousands) Series A 10,000,000 9,486,575 $ 9,486 $ 9,486 Series B 35,000,000 7,866,175 7,866 9,232 Series C 8,000,000 7,500,000 7,500 5,550 Series D 20,000,000 8,708,352 13,063 12,415 Total 73,000,000 33,561,102 $ 37,915 $ 36,683 For the years ended December 31, 2019 and 2018, the Company issued 114,445 and 2,592,000 shares of Series B convertible preferred stock, respectively, at $1.00 per share. For the year ended December 31, 2019, the Company issued 1,509,335 shares of Series D convertible preferred stock at $1.50 per share, of which 1,166,667 shares related to the settlement with PUR. See Note 6 – Investment in PUR for further information. For the year ended December 31, 2018, the Company issued 1,742,167 shares of Series D convertible preferred stock at $1.50 per share. General Rights and Preferences The holders of each series of convertible preferred stock are entitled to receive noncumulative dividends at a rate of 6% per share per annum based on the original issue price. The preferred stock dividends are payable in preference and in priority to any dividends on common stock if or when any dividends are declared by the Board of Directors. The Company’s Board of Directors have not declared any dividends during the periods presented. The holders of the Series A, B and C convertible preferred stock are entitled to receive liquidation preferences at the rate of $1.00 per share. The Series D holders are entitled to liquidation preferences at a rate of $1.50 per share. All series holders also have a right to receive declared but unpaid dividends upon a liquidation event. The liquidation preferences to all holders of preferred stock are made pari passu The shares of each series of convertible preferred stock are convertible into an equal number of shares of common stock, at the option of the holder. Likewise, at the election of the holders of the majority of the then outstanding shares of convertible preferred stock, all shares will automatically convert to an equal number of shares of common stock. Finally, each share of preferred stock is automatically converted into common stock immediately upon the Company’s sale of its common stock in a firm commitment underwritten public offering pursuant to a registration statement under the Securities Act of 1933, as amended, resulting in the receipt by the Company of at least $20.0 million in which the per share price is at least $4.50. The conversion from the public offering would result in the convertible preferred stockholders receiving less than one common share for each of their shares being converted. The holders of each series of preferred stock are entitled to one vote for each share of common stock into which such preferred stock could then be converted; and with respect to such vote, such holders shall have full voting rights and powers equal to the voting rights and powers of the holders of common stock. Non-Dilutive Special non-dilutive one-time

Warrants

Warrants	12 Months Ended
	Dec. 31, 2019
Text Block [Abstract]
Warrants	13. Warrants Common Warrants On January 1, 2016, the Company granted warrants to purchase common stock to Gar Wood Securities, LLC (“Gar Wood”) as consideration for settlement of prior liability claims. The warrants entitled Gar Wood to purchase up to 25,000 common shares at an exercise price of $3.31 per share up until the expiration date of July 31, 2021. The fair value of the warrant was determined to be immaterial using the Black-Scholes option pricing model. The warrants remain outstanding and unexercised as of December 31, 2019 and 2018. Convertible Preferred Stock Warrants On February 26, 2010, the Company issued warrants to purchase 300,000 shares of Series A convertible preferred stock in exchange for rent on a premise lease at an exercise price of $1.00 per share, which expired unexercised on December 31, 2019. The warrants were classified as a component of warrant liabilities on the consolidated balance sheets as of December 31, 2018. On October 20, 2016, the Company issued warrants to purchase 450,000 shares of Series B convertible preferred stock as part of a settlement of compensation for advisory services at an exercise price of $1.00 per share, which expired unexercised on December 31, 2019. The warrants are classified as a component of warrant liabilities on the consolidated balance sheets as of December 31, 2018.

Stock-Based Compensation Expens

Stock-Based Compensation Expense	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation Expense	14. Stock-Based Compensation Expense The Company established the Histogen Inc. 2007 Stock Plan (the “2007 Plan”) effective as of November 28, 2007. The Company was authorized to issue 14 million shares of common stock to employees, directors and consultants under the 2007 Plan. The 2007 Plan permits the issuance of incentive stock options (ISOs), non-statutory On December 18, 2017, the Company established the Histogen Inc. 2017 Stock Plan (the “2017 Plan”). Under the 2017 Plan, the Company is authorized to issue a maximum aggregate of 5.8 million shares of common stock with adjustments for unissued or forfeited shares under the predecessor plan. In April 2019, the Company amended the 2017 Plan, which increased the number of common stock available for grants by 2,278,007 shares. The 2017 Plan retained substantially all of the terms of the 2007 Plan and expires in December of 2027. Performance-based Stock Options On January 24, 2019, the Company issued 3,382,923 stock options to its newly appointed Chief Executive Officer. In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months. On January 28, 2020, the award agreement was amended whereby the 40% of stock options (“Liquidity Option Shares”) subject to vesting upon an initial public offering or 45 days following a change in control will now vest immediately upon meeting certain performance-based criteria. The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) upon the date that the market capitalization of the combined company exceeds $200,000,000; (3) upon the date that the market capitalization of the combined company exceeds $275,000,000, and; (4) upon the date that the market capitalization of the combined company exceeds $300,000,000. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination. Recognition of stock-based compensation associated with performance-based stock options commences when the performance criteria is probable of achievement, using management’s best estimates. As of December 31, 2019, none of the performance-based stock options were exercisable because none of the performance-based criteria had been achieved. Because achievement of any of the performance-based criteria was not deemed probable as of December 31, 2019, the Company did not record any expense for these stock options through December 31, 2019. The following summarizes activity related to the Company’s stock options under the 2007 Plan and 2017 Plan for the years ended December 31, 2019 and 2018: Options Weighted- Weighted-average Aggregate Outstanding at December 31, 2017 5,730,000 $ 0.17 5.10 $ 2,174 Granted 1,400,000 0.57 Exercised (790,000 ) 0.14 Cancelled / Forfeited (190,000 ) 0.42 Outstanding at December 31, 2018 6,150,000 $ 0.26 5.60 $ 3,098 Granted 3,722,923 0.76 Exercised (250,000 ) 0.14 Cancelled / Forfeited (125,000 ) 0.63 Outstanding at December 31, 2019 9,497,923 $ 0.45 6.34 $ 2,926 Vested and exercisable at December 31, 2019 5,272,552 $ 0.23 4.24 $ 2,814 For the year ended December 31, 2019, the Company granted its employees and directors 3.7 million stock options at a weighted-average grant date fair value per share equal to $0.49. For the year ended December 31, 2018, the Company granted its employees and directors 1.2 million stock options and non-employees As of December 31, 2019 and 2018, the unrecognized compensation costs related to outstanding stock options (excluding those with unachieved performance-based conditions) was $1.1 million and $373 thousand, respectively, which was expected to be recognized as expense over approximately 2.9 years and 2.3 years, respectively. For the year ended December 31, 2019, 250,000 stock options were exercised pursuant to a cashless exercise, whereby 45,231 shares were forfeited to cover the aggregate exercise price and the remaining 204,769 shares were issued to the holders. For the year ended December 31, 2018, 225,000 stock options were exercised pursuant to a cashless exercise, whereby 63,637 shares were forfeited to cover the aggregate exercise price and the remaining 161,363 shares were issued to the holders. The total intrinsic value, which is the amount by which the exercise price was exceeded by the fair value of the Company’s common stock on the date of exercise, of stock options exercised during the year ended December 31, 2019 was $129 thousand. Valuation of Stock Option Awards The following weighted-average assumptions were used to calculate the fair value of awards granted to employees, directors and non-employees: Years Ended December 31, 2019 2018 Expected volatility 70.0 % 63.9 % Risk-free interest rate 2.5 % 2.8 % Expected option life (in years) 6.25 6.25 Expected dividend yield 0.0 % 0.0 % Compensation Costs The compensation cost that has been included in the Company’s consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Years Ended December 31, 2019 2018 Cost of product revenues $ 38 $ 25 Research and development 34 54 General and administrative 366 247 Total $ 438 $ 326 Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows: December 31, 2019 Common stock warrants 25,000 Convertible preferred stock (if converted) 35,184,882 Common stock options issued and outstanding 9,497,923 Common stock available for issuance under the 2007 Plan — Common stock available for issuance under the 2017 Plan 3,391,412 48,099,217

Noncontrolling Interest

Noncontrolling Interest	12 Months Ended
	Dec. 31, 2019
Noncontrolling Interest [Abstract]
Noncontrolling Interest	15. Noncontrolling Interest Noncontrolling interest represents the balances and results attributable to the other member of the consolidated VIE, AB, not included in the stockholders’ deficit of the Company. A summary of changes in the Company’s ownership of AB for the years ended December 31, 2019 and 2018 is as follows (in thousands): Years Ended December 31, 2019 2018 Net loss attributable to Histogen, Inc. stockholders $ (2,966 ) $ (6,125 ) Decrease in Histogen, Inc.’s paid-in — (100 ) Change from net loss attributable to Histogen, Inc. stockholders and transfers to noncontrolling interest $ (2,966 ) $ (6,225 )

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2019
Text Block [Abstract]
Regulatory Matters	17. Regulatory Matters On November 12, 2015, the Company received notice that it was placed on clinical hold by the U.S. FDA after filing an IND in October 2015 to initiate Phase 1 clinical development of the lead product, HSC. The FDA required additional information, chiefly related to the characterization strategy of the product. In February of 2017, the Company became aware of unauthorized releases of HSC at the direction of the Company’s then CEO to certain related parties in the absence of an active investigational new drug (“IND”). At that time, the Board of Directors immediately engaged an independent law firm to conduct a full investigation of the matter which led to several corrective actions. Moreover, the results of the investigation found no recipients of the material suffering any adverse reactions or injuries from the released material. On May 16, 2017, at the direction of the Board and investigative counsel, the Company self-reported the incidents, the follow up investigation and the corrective measures, which included additional quality controls and procedures, in a formal disclosure to the FDA. In March of 2018, the Company filed a formal response letter to the clinical hold with the FDA containing completed test results and additional information requested by the FDA. On May 3, 2018 the Company received a release from full clinical hold from the FDA to continue its IND activity. With an active IND, the Company conducted its planned clinical trial with HSC and observed no Serious Adverse Events. The trial was completed in January 2019 and the final Clinical Study Report was submitted to the FDA in June 2019. There were no material impacts to the consolidated financial statements related to the above activity for the years ended December 31, 2019 and 2018.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2019
Employee Benefit Plans	18. Employee Benefit Plans The Company sponsors a qualified 401(k) savings plan (“401k Plan”) for all eligible employees. Participants may contribute between 1% and 100% of their eligible compensation, subject to IRS regulations. The 401k Plan provides that the Company can make discretionary contributions of 25% of the employees’ salary deferrals up to a maximum of $2,500 per each employee. Employer contributions under the 401k Plan for the years ended December 31, 2019 and 2018, were $0 and approximately $37 thousand, respectively.
Predecessor Company [Member]
Employee Benefit Plans	10. Employee Benefits Effective December 4, 2006, the Company has a defined contribution 401(k) plan for its employees. Employees are eligible to participate in the plan beginning on the first day of employment. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation. Effective January 1, 2007, the Company instituted a safe harbor matching contribution program. Contributions to the matching program totaled $192,000, $239,000 and $217,000 for the years ended December 31, 2019, 2018 and 2017, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes	19. Income Taxes At December 31, 2019, the Company had federal and California net operating loss (“NOL”) carryforwards of approximately $38.3 million and $38.1 million, respectively. The federal net operating loss carryforwards of $7.6 million generated during the years ended December 31, 2019 and 2018 will carryforward indefinitely and be available to offset up to 80% of future taxable income. The $30.7 million and $30.5 million of carryforwards for federal and California income tax purposes, respectively, that were generated prior to 2018 begin to expire in 2028, unless previously utilized. At December 31, 2019, the Company had federal and California research and development (R&D) credit carryforwards of approximately $0.9 million and $0.8 million, respectively. The federal R&D tax credit carryforwards will begin to expire in 2027 unless previously utilized. The California R&D credit carryforwards will carry forward indefinitely. The Company recognizes the impact of a tax position in the financial statements only if that position is more likely than not of being sustained upon examination by taxing authorities, based on the technical merits of the position. Any interest and penalties related to uncertain tax positions will be reflected in income tax expense. Under Sections 382 and 383 of the Internal Revenue Code (IRC), substantial changes in the Company’s ownership may limit the amount of NOL and research and development credit carryforwards that could be used annually in the future to offset taxable income. The tax benefits related to future utilization of federal and state NOL carryforwards, credit carryforwards, and other deferred tax assets may be limited or lost if cumulative changes in ownership exceeds 50% within any three-year period. The Company has not completed an IRC Section 382/383 analysis regarding the limitation of net operating loss and research and development credit carryforwards, and therefore, the ability of the Company to utilize its NOL and R&D credits is unknown. The Company accounts for income taxes using the asset and liability method to compute the differences between the tax basis of assets and liabilities and the related financial amounts, using currently enacted tax rates. The deferred tax assets and liabilities reflect the future tax consequences of the differences between the financial reporting and tax basis of assets and liabilities using currently enacted tax rates. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax assets will be realized. The provision for income taxes based on losses from operations consists of the following (in thousands): Years Ended December 31, 2019 2018 Current Federal $ — $ — State (1 ) (1 ) Total (1 ) (1 ) Deferred Federal 736 1,277 State 180 455 Total 916 1,732 Less valuation allowance (916 ) (1,732 ) Income tax expense $ (1 ) $ (1 ) The Company records a valuation allowance against deferred tax assets to the extent that it is more likely than not that some portion, or all, the deferred tax assets will not be realized. Due to the substantial doubt related to the Company’s ability to utilize its deferred tax assets, the Company recorded a valuation allowance against the deferred tax assets. The change in the valuation allowance is an increase of $0.9 million and $1.7 million for the years ended December 31, 2019 and 2018, respectively. The reconciliation of income taxes computed using the statutory U.S. income tax rate and the provision (benefit) for income taxes for the years ended December 31, 2019 and 2018, are as follows (in thousands): Years Ended December 31, 2019 2018 Tax computed at federal statutory rate $ (589 ) 21.00 % $ (1,256 ) 21.00 % State tax, net of federal tax benefits (194 ) 6.92 % (392 ) 6.56 % Permanent items 5 (0.18 %) 104 (1.74 %) Tax credits (66 ) 2.35 % (157 ) 2.62 % Tax rate change 0 0.00 % (18 ) 0.31 % Valuation allowance increase 916 (32.65 %) 1,732 (28.74 %) Other (71 ) 2.53 % (12 ) 0.01 % Provision for income taxes $ 1 (0.04 %) $ 1 0.01 % Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2019 2018 Tax loss carryforward $ 10,757 $ 9,986 R&D credits and other tax credits 1,540 1,455 Stock-based compensation 60 71 Other 947 876 Total deferred tax assets 13,304 12,388 Less valuation allowance (13,304 ) (12,388 ) Deferred tax assets, net $ — $ — Uncertain Tax Positions The FASB ASC Topic 740, Income Taxes 740-10, The following table reconciles the beginning and ending amount of unrecognized tax benefits for the fiscal years ended December 31, 2019 and 2018 (in thousands): Years Ended December 31, 2019 2018 Gross unrecognized tax benefits at the beginning of the year $ — $ — Additions from tax positions taken in the current year 108 — Additions from tax positions taken in prior years 366 — Gross unrecognized tax benefits at end of the year $ 474 $ — Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate. The Company does not anticipate that there will be a substantial change in unrecognized tax benefits within the next twelve months. The Company has not recognized any interest and penalties related to income taxes in the accompanying consolidated balance sheets or statements of operations. The Company is subject to taxation in the U.S. and state jurisdictions. The Company’s income tax returns for 2017, 2018 and 2019 are still open to audit by the taxing authorities. US Tax Reform On December 22, 2017, the 2017 Tax Cuts and Jobs Act (Tax Act) was enacted into law and the new legislation contains several key tax provisions that affected the Company, including a reduction of the corporate income tax rate to 21% effective January 1, 2018, among others. The Company is required to recognize the effect of the tax law changes in the period of enactment, such as determining the transition tax, remeasuring the Company’s U.S. deferred tax assets and liabilities, as well as reassessing the net realizability of the Company’s deferred tax assets and liabilities. In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (SAB 118), which allowed the Company to record provisional amounts during a measurement period not to extend beyond one year of the enactment date. As a result, the Company previously provided a provisional estimate of the effect of the Tax Act in the Company’s financial statements. In the fourth quarter of 2018, the Company completed its analysis to determine the effect of the Tax Act and recorded no material adjustments as of December 31, 2018.
Predecessor Company [Member]
Income Taxes	8. Income Taxes Significant components of the Company’s deferred tax assets at December 31, 2019 and 2018 are shown below (in thousands): December 31, 2019 2018 Deferred tax assets Net operating loss carryovers $ 35,901 $ 31,135 Research and development tax credits 8,312 8,641 Intangibles 130 379 Stock options 438 2,255 Compensation 47 452 Deferred revenue — 2,642 Other 88 62 Total gross deferred tax assets 44,916 45,566 Deferred tax liabilities Right-of-use 46 — Total net deferred tax assets 44,870 45,566 Less valuation allowance (44,870 ) (45,566 ) Net deferred tax assets $ — $ — A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2019, 2018 and 2017 is as follows: December 31, 2019 2018 2017 Statutory rate 21.0 % 21.0 % 34.0 % Valuation allowance 6.1 % (25.2 )% 51.5 % Federal tax rate change — % — % (93.3 )% General business credits (2.9 )% 6.2 % 10.8 % Expiration of stock options (21.4 )% — % — % Other (2.8 )% (2.0 )% (3.0 )% Effective tax rate — % — % — % At December 31, 2019, the Company had federal and state NOL carryforwards of $145.5 million and $76.4 million, respectively. The federal and state NOL carryforwards begin to expire in 2028, unless previously utilized. The federal NOL carryforwards generated after 2017 have an indefinite carryforward life. The Company also has federal, including orphan drug, and state research credit carryforwards of $8.3 million and $2.4 million, respectively. The federal research credit carryforwards will begin expiring in 2027, unless previously utilized. The state research credit will carry forward indefinitely. The change in the valuation allowance is a decrease of $0.7 million for the year ended December 31, 2019, an increase of $4.4 million for the year ended December 31, 2018 and a decrease of $9.0 million for the year ended December 31, 2017. Pursuant to Internal Revenue Code (IRC) Sections 382 and 383, annual use of the Company’s NOL or research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. The Company previously completed a study to assess whether an ownership change, as defined by IRC Section 382, had occurred from its formation through December 31, 2017. Based upon this study, the Company determined that ownership changes had occurred in 2006 and 2013 but concluded that the annual utilization limitation would be sufficient to utilize the Company’s pre-ownership The following table summarizes the activity related to the Company’s unrecognized tax benefits (in thousands): 2019 2018 2017 Balance at beginning of year $ 2,221 $ 1,932 $ 1,319 Additions based on tax positions related to the current year — 289 613 Reductions based on tax positions related to prior years (80 ) — — Balance at end of year $ 2,141 $ 2,221 $ 1,932 The Company does not expect that the unrecognized tax benefits will change within 12 months of this reporting date. Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate. The Company’s policy is to recognize interest and penalties related to income tax matters in income tax expense. For the years ended December 31, 2019, 2018 and 2017, the Company has not recognized any interest or penalties related to income taxes. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by the federal and state jurisdictions where applicable. There are currently no pending income tax examinations. The Company’s tax years for 2005 and forward are subject to examination by the federal and California tax authorities due to the carryforward of unutilized net operating losses (NOLs) and research and development credits.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Fair Value Measurements	3. Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Includes financial instruments for which quoted market prices for identical instruments are available in active markets. Level 2: Includes financial instruments for which there are inputs other than quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transaction (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. Level 3: Includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions. Below is a summary of assets, including cash, cash equivalents and marketable securities, measured at fair value as of December 31, 2019 and 2018 (in thousands): Fair Value Measurements Using December 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 1,870 $ 1,870 $ — $ — Money market funds 18,833 18,833 — — Total $ 20,703 $ 20,703 $ — $ — Fair Value Measurements Using December 31, 2018 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 2,072 $ 2,072 $ — $ — Money market funds 8,000 8,000 — — Corporate debt securities 30,620 — 30,620 — Total $ 40,692 $ 10,072 $ 30,620 $ — At December 31, 2018, the Company’s marketable securities, consisting principally of debt securities, are classified as available-for-sale,

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Marketable Securities	4. Marketable Securities The Company invests its excess cash in money market funds and debt instruments of financial institutions, corporations, government sponsored entities and municipalities. The Company had no investments in marketable securities at December 31, 2019, the following tables summarize the Company’s investments in marketable securities at December 31, 2018 (in thousands): As of December 31, 2018 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 29,144 $ — $ (17 ) $ 29,127 Total $ 29,144 $ — $ (17 ) $ 29,127

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Notes Payable	6. Notes Payable In July 2010, the Company issued to Pfizer Inc. (Pfizer) a $1.0 million promissory note (the Pfizer Note). The Pfizer Note bore interest at a rate of 7% per annum and was scheduled to mature on July 29, 2020. Interest was payable on a quarterly basis. On January 24, 2017, the Company voluntarily prepaid the entire balance of the outstanding principal and accrued and unpaid interest of the Pfizer Note in the amount of $1,004,861. Prior to the prepayment of the Pfizer Note, the Company recorded the Pfizer Note on the balance sheet at face value. Based on borrowing rates available to the Company for loans with similar terms, the Company believed that the fair value of the Pfizer Note approximated its carrying value. The fair value measurement was categorized within Level 3 of the fair value hierarchy. On February 15, 2017, the Company issued a convertible promissory note (the Novartis Note) in the principal amount of $15.0 million, pursuant to the Investment Agreement. The Novartis Note bore interest on the unpaid principal balance at a rate of 6% per annum and had a scheduled maturity date of December 31, 2019. The terms of the Novartis Note allowed the Company to convert the principal and accrued interest into the Company’s common stock at a conversion price equal to 120% of the 20-day The Company elected to account for the Novartis Note under the fair value option. Prior to conversion of the Novartis Note, the Company concluded that the fair value of the Novartis Note remained at $12.5 million, plus the related accrued interest, due to its conversion features. The fair value measurement was categorized within Level 2 of the fair value hierarchy.

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Collaboration and License Agreements	9. Collaboration and License Agreements In December 2016, the Company entered into the Collaboration Agreement, pursuant to which the Company granted Novartis an exclusive option to collaborate with the Company to develop products containing emricasan. Pursuant to the Collaboration Agreement, the Company received a non-refundable In May 2017, Novartis exercised its option under the Collaboration Agreement. In July 2017, the Company received a $7.0 million option exercise payment, at which time the license under the Collaboration Agreement became effective (the License Effective Date). The Company and Novartis entered into an amendment to the Collaboration Agreement, pursuant to which they mutually agreed to terminate the Collaboration Agreement in September 2019. Under the Collaboration Agreement, the Company was eligible to receive up to an aggregate of $650.0 million in milestone payments over the term of the Collaboration Agreement, contingent on the achievement of certain development, regulatory and commercial milestones, as well as royalties or profit and loss sharing on future product sales in the United States, if any. Novartis was to pay 50% of the Company’s Phase 2b and observational study costs pursuant to an agreed upon budget. Upon completion of the Phase 2b trials, Novartis would have assumed 100% of the observational study costs and full responsibility for emricasan’s Phase 3 development and all combination product development. Due to the termination of the Collaboration Agreement, the Company will not receive any future milestone, royalty or profit and loss sharing payments under the Collaboration Agreement. Pursuant to the terms of termination of the Collaboration Agreement, the Company and Novartis continued to share the costs of the Phase 2b trials equally until December 31, 2019, and Novartis will pay up to $150,000 for its share of the costs of the Phase 2b trials, if any, in 2020. The Company accounted for the termination of the Collaboration Agreement as a contract modification of an existing contract as the remaining services are not distinct and, therefore, form part of a single performance obligation that is partially satisfied as of the contract modification date. Concurrent with entry into the Collaboration Agreement, the Company entered into the Investment Agreement, whereby the Company was able to borrow up to $15.0 million at a rate of 6% per annum, under one or two notes, with a maturity date of December 31, 2019. On February 15, 2017, the Company issued the Novartis Note in the principal amount of $15.0 million pursuant to the Investment Agreement. The terms of the Novartis Note allowed the Company to convert the principal and accrued interest into the Company’s common stock at a conversion price equal to 120% of the 20-day Under the Collaboration Agreement, there were two significant performance obligations: the license and the research and development services, but the license was not distinct from the research and development services as Novartis could not obtain value from the license without the research and development services, which the Company was uniquely able to perform. The Company concluded that progress towards completion of the performance obligations related to the Collaboration Agreement was best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The transaction price recognized as revenue under the Collaboration Agreement consisted of the upfront payment, option exercise fee, deemed revenue from the premium paid by Novartis under the Investment Agreement and estimated reimbursable research and development costs. Certain expenses directly related to execution of the Collaboration Agreement were capitalized as assets on the balance sheet and were expensed in a manner consistent with the methodology used for recognizing revenue. During the quarter ended June 30, 2019, as a result of the decision to discontinue the development of emricasan, the Company significantly reduced the transaction price and the total estimated reimbursable research and development expenses under the Collaboration Agreement. The net effect of these changes resulted in the recognition of a cumulative catch-up A reconciliation of the opening and closing balances of deferred revenue related to the Collaboration Agreement, which represents the unrecognized balance of the transaction price, is as follows (in thousands): Deferred Revenue Balance at December 31, 2017 $ 26,691 Cumulative effect of adoption of accounting standard 1,299 Additions to deferred revenue 18,486 Revenue recognized (33,586 ) Balance at December 31, 2018 12,890 Additions to deferred revenue 8,826 Revenue recognized (21,716 ) Balance at December 31, 2019 $ — A reconciliation of the opening and closing balances of deferred costs related to execution of the Collaboration Agreement is as follows (in thousands): Deferred Costs Balance at December 31, 2017 $ — Cumulative effect of adoption of accounting standard 687 Costs recognized (377 ) Balance at December 31, 2018 310 Costs recognized (310 ) Balance at December 31, 2019 $ —

Quarterly Financial Data (unaud

Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Quarterly Financial Data (unaudited)	12. Quarterly Financial Data (unaudited) The following tables summarize the unaudited quarterly financial data for the last two fiscal years (in thousands, except per share data): 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 7,024 $ 10,791 $ 3,376 $ 526 Total operating expenses 11,974 11,619 6,759 3,371 Total other income 203 172 130 116 Net loss (4,747 ) (656 ) (3,253 ) (2,729 ) Net loss per share, basic and diluted (1) (1.43 ) (0.20 ) (0.98 ) (0.82 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 9,737 $ 8,774 $ 7,666 $ 7,409 Total operating expenses 14,794 13,331 12,324 11,414 Total other income 39 60 69 99 Net loss (5,018 ) (4,497 ) (4,589 ) (3,906 ) Net loss per share, basic and diluted (1) (1.67 ) (1.49 ) (1.52 ) (1.26 ) (1) Net loss per share is computed independently for each quarter and the full year based upon respective shares outstanding; therefore, the sum of the quarterly net loss per share amounts may not equal the annual amounts reported.

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Restructuring Costs	13. Restructuring Costs In June 2019, the Company announced a restructuring plan that included reducing staff and suspending development of its inflammasome disease candidate, CTS-2090, one-time In September 2019, the Company announced a second restructuring plan that included reducing additional staff. As a result, during the three months ended September 30, 2019, the Company recognized one-time At December 31, 2019, the remaining accrued severance liability totals approximately $0.1 million.

Description of Business, Basi_2

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Description of Business	Description of Business Histogen Inc. (the “Company,” “Histogen,” or the “combined company”), formerly known as Conatus Pharmaceuticals Inc. (“Conatus”), was incorporated in the state of Delaware on July 13, 2005. The Company is a clinical-stage therapeutics company focused on developing potential first-in-class The Company’s lead drug candidate, HST-001, HST-001 HST-002 HST-003 non-prescription pan-caspase COVID-19
Merger between Private Histogen and Conatus Pharmaceuticals Inc. and Name Change	Merger between Private Histogen and Conatus Pharmaceuticals Inc. and Name Change On January 28, 2020, the Company, then operating as Conatus, entered into an Agreement and Plan of Merger and Reorganization, as amended (the “Merger Agreement”), with privately-held Histogen Inc. (“Private Histogen”) and Chinook Merger Sub, Inc., a wholly-owned subsidiary of the Company (“Merger Sub”). Under the Merger Agreement, Merger Sub merged with and into Private Histogen, with Private Histogen surviving as a wholly-owned subsidiary of the Company (the “Merger”). On May 26, 2020, the Merger was completed. Conatus changed its name to Histogen Inc., and Private Histogen, which remains as a wholly-owned subsidiary of the Company, changed its name to Histogen Therapeutics Inc. On May 27, 2020, the combined company’s common stock began trading on The Nasdaq Capital Market under the ticker symbol “HSTO”. Except as otherwise indicated, references herein to “Histogen,” the “Company,” or the “combined company”, refer to Histogen Inc. on a post-Merger basis, and the term “Private Histogen” refers to the business of privately-held Histogen Inc., prior to completion of the Merger. References to Conatus refer to Conatus Pharmaceuticals Inc. prior to completion of the Merger. Pursuant to the terms of the Merger Agreement, each outstanding share of Private Histogen common stock outstanding immediately prior to the closing of the Merger was converted into approximately 0.14342 shares of Company common stock (the “Exchange Ratio”), after taking into account the Reverse Stock Split, as defined below. Immediately prior to the closing of the Merger, all shares of Private Histogen preferred stock then outstanding were exchanged into shares of common stock of Private Histogen. In addition, all outstanding options exercisable for common stock of Private Histogen and warrants exercisable for common stock of Private Histogen became options and warrants exercisable for the same number of shares of common stock of the Company multiplied by the Exchange Ratio. Immediately following the Merger, stockholders of Private Histogen owned approximately 71.3% of the outstanding common stock of the combined company. The transaction was accounted for as a reverse asset acquisition in accordance with generally accepted accounting principles in the United States of America (“GAAP”). Under this method of accounting, Private Histogen was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the facts that, immediately following the Merger: (i) Private Histogen’s stockholders owned a substantial majority of the voting rights in the combined company, (ii) Private Histogen designated a majority of the members of the initial board of directors of the combined company, and (iii) Private Histogen’s senior management holds all key positions in the senior management of the combined company. As a result, as of the closing date of the Merger, the net assets of the Company were recorded at their acquisition-date relative fair values in the accompanying condensed consolidated financial statements of the Company and the reported operating results prior to the Merger are those of Private Histogen.
Reverse Stock Split and Exchange Ratio	Reverse Stock Split and Exchange Ratio On May 26, 2020, in connection with, and prior to the completion of, the Merger, the Company effected a one-for-ten
Liquidity and Going Concern	Liquidity and Going Concern From inception and through September 30, 2020, the Company has accumulated losses of $59.2 million and expects to incur operating losses and generate negative cash flows from operations for the foreseeable future. As of September 30, 2020, the Company had $6.6 million in cash and cash equivalents. The Company has not yet established ongoing sources of revenues sufficient to cover its operating costs and will need to continue to raise additional capital to support its future operating activities, including progression of its development programs, preparation for commercialization, and other operating costs. Management’s plans with regard to these matters include entering into a combination of additional debt or equity financing arrangements, government funding, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. In addition, the Company may fund its losses from operations through the common stock purchase agreement the Company entered into with Lincoln Park in July 2020, for the purchase of up to $10.0 million of the Company’s common stock over the 24 month period of the purchase agreement, $8.5 million of which remains available for sale as of the date these condensed consolidated financial statements were available to be issued (see Note 9), subject to limitations on the amount of securities the Company may sell under its effective registration statement on Form S-3 The condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. Based on the above, there is substantial doubt about the Company’s ability to continue as a going concern within one year from the date the condensed consolidated financial statements are available to be issued. The condensed consolidated financial statements do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the outcome of this uncertainty.
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its controlled subsidiaries, including Histogen Therapeutics, Inc., and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). All intercompany balances and transactions have been eliminated upon consolidation. The Company acquired Centro De Investigacion de Medicina Regenerativa, S.A. de C.V. (“CIMRESA”), a company in Mexico, during 2018 to facilitate a potential clinical development program for HSC. This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to FDA). CIMRESA had no operational or financial activity for the three and nine months ended September 30, 2020 and 2019. The Company holds a majority interest in Adaptive Biologix, Inc. (“AB”, formerly Histogen Oncology, LLC). AB was formed to develop and market applications for the treatment of cancer. The Company consolidates AB into its condensed consolidated financial statements.
Reclassifications	Reclassifications Certain prior period amounts related to the acquisition of in-process in-process
Unaudited Interim Financial Information	Unaudited Interim Financial Information The unaudited condensed consolidated financial statements as of September 30, 2020, and for the three and nine months ended September 30, 2020 and 2019, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) and GAAP. Accordingly, these condensed consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of Management, these unaudited interim condensed consolidated financial statements contain all adjustments necessary, all of which are of a normal and recurring nature, to present fairly the Company’s financial position, results of operations and cash flows. Interim results are not necessarily indicative of results for a full year or future periods. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended December 31, 2019 included in our prospectus dated April 1, 2020, filed with the Securities and Exchange Commission pursuant to Rule 424(b) under the Securities Act, relating to the Registration Statement on Form S-4, No. 333-236332).
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the periods presented. Management believes that these estimates and assumptions are reasonable, however, actual results may differ and could have a material effect on future results of operations and financial position. Though the impact of the COVID-19 Significant estimates and assumptions include the useful lives of property and equipment, discount rates used in recognizing contracts containing leases, unrecognized tax benefits, reserves for excess or obsolete inventory, stock-based compensation, and best estimate of standalone selling price of revenue deliverables. Actual results may materially differ from those estimates.	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the years presented. Management believes that these estimates and assumptions are reasonable, however, actual results may differ and could have a material effect on future results of operations and financial position. Significant estimates and assumptions include the allowance for doubtful accounts, useful lives of property and equipment, unrecognized tax benefits, potential reserves for excess or obsolete inventory, the fair value of warrant and indemnification liabilities, the fair value of the Company’s common stock, stock-based compensation, and best estimate of selling price of revenue deliverables. Actual results may materially differ from those estimates.
Variable Interest Entities	Variable Interest Entities The Company determined that AB is a variable interest entity (“VIE”) and that the Company is its primary beneficiary. The Company holds greater than 50% of the shares and has the authority to manage the business and affairs of the VIE. AB’s other shareholder does not have a controlling interest. On January 12, 2018, AB was converted into a traditional C corporation, a Delaware corporation, under a Plan of Conversion agreement between the Company and the other member of the limited liability company, Wylde, LLC (“Wylde”). The entity structure change eliminated some of the special rights Wylde had under the LLC charter and gave the Company more control over the voting rights under the new corporate structure. The Plan of Conversion called for 3,800,000 common stock shares of AB to be issued to the Company and Wylde in proportion to their interest in the LLC immediately before the agreement was executed. Contemporaneously, the Company offered to purchase, and Wylde agreed to sell, 100,000 of the AB common shares for $1.00 per share for a total price of $0.1 million. The completion of this transaction among the stockholders of AB resulted in Histogen owning 2,600,000 common shares or approximately 68% of AB. A VIE is typically an entity for which the Company has less than a 100% equity interest but controls the decision making over the business and affairs of the entity, directs the decisions driving the economic performance of such entity and participates in the profit and losses of such an entity. The Company weighed both quantitative and qualitative information about the different risks and reward characteristics of each entity and the significance of that entity to the consolidating group in the aggregate.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, the Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with an original maturity date of ninety days or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking, money market accounts and brokerage accounts. The Company’s current restricted cash consists of cash held as collateral for the issuer of its credit card accounts. Noncurrent restricted cash consists of collateral for a letter of credit issued as a security deposit for the lease of the Company’s headquarters and is required to be held throughout the lease term.	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with an original maturity date of ninety days or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking, money market accounts and brokerage accounts. Restricted cash consists of cash held as collateral for the issuer of its credit card accounts.
Risks and Uncertainties	Risks and Uncertainties Credit Risk At certain times throughout the year, the Company may maintain deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institutions in which those deposits are held. Customer Risk During the three months ended September 30, 2020 and 2019, one customer accounted for 100% and 39% of total revenues, respectively. During the nine months ended September 30, 2020 and 2019, one customer accounted for 100% and 94% of total revenues, respectively. Accounts receivable from the customer was $0.1 million at September 30, 2020 and December 31, 2019. COVID-19 On January 30, 2020, the World Health Organization (“WHO”) announced a global health emergency because of a new strain of coronavirus originating in Wuhan, China (the “COVID-19 outbreak”) and the risks to the international community as the virus spreads globally beyond its point of origin. In March 2020, the WHO classified the COVID-19 outbreak as a pandemic, based on the rapid increase in exposure globally. The full impact of the COVID-19 outbreak continues to evolve as of the date these condensed consolidated financial statements were available to be issued. As such, it is uncertain as to the full magnitude that the pandemic will have on the Company’s financial condition, liquidity, and future results of operations. Management is actively monitoring the situation on its financial condition, liquidity, operations, customers, suppliers, industry, and workforce. Given the daily evolution of the COVID-19 outbreak and the response to curb its spread, the Company is not able to estimate the effects of the COVID-19 outbreak to its results of operations, financial condition, or liquidity for fiscal year 2020. On March 27, 2020, President Trump signed into law the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”). The CARES Act, among other things, includes provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations, increased limitations on qualified charitable contributions and technical corrections to tax depreciation methods for qualified improvement property. The Company continues to examine the impact that the CARES Act may have on its business. Currently, the Company is unable to determine the impact that the CARES Act will have on its financial condition, results of operations, or liquidity. The CARES Act also appropriated funds for the U.S. Small Business Administration Paycheck Protection Program (“PPP”) loans that are forgivable in certain situations to promote continued employment, as well as Economic Injury Disaster Loans to provide liquidity to small businesses harmed by COVID-19. Refer to Note 8 — Paycheck Protection Program Loan for further information.
Accounts Receivable	Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. The allowance is based on an analysis of historical bad debt, current receivables aging and expected future write-offs of uncollectible accounts, as well as an assessment of specific identifiable accounts considered at risk or uncollectible. Additions to the allowance for doubtful accounts include provisions for bad debt and deductions from the allowance for doubtful accounts include customer write-offs. Provision for doubtful accounts was not material for all periods presented.
Inventories	Inventories Inventories, consisting of raw materials, work in process, and finished goods, are valued at the lower of cost (first-in, first-out	Inventories Inventories, consisting of raw materials, work in process, and finished goods, are valued at the lower of cost (first-in, first-out
Property and Equipment	Property and Equipment Property and equipment are reported net of accumulated depreciation and amortization and are comprised of office furniture and equipment, lab and manufacturing equipment, and leasehold improvements. Ordinary maintenance and repairs are charged to expense, while expenditures that extend the physical or economic life of the assets are capitalized. Furniture and all equipment are depreciated over their estimated useful lives, or five years, using the straight-line method. Leasehold improvements are amortized over their estimated useful lives and limited by the remaining term of the building lease, using the straight-line method.	Property and Equipment Property and equipment are reported net of accumulated depreciation and amortization and are comprised of office furniture and equipment, lab and manufacturing equipment, and leasehold improvements. Ordinary maintenance and repairs are charged to expense, while expenditures that extend the physical or economic life of the assets are capitalized. Furniture and all equipment are depreciated over their estimated economic lives, or five years, using the straight-line method. Leasehold improvements are amortized over their estimated useful lives and limited by the remaining term of the building lease, using the straight-line method.
Long-Lived Assets	Valuation of Long-Lived Assets Long-lived assets to be held and used, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. As of September 30, 2020, the Company has not recognized any impairment to long-lived assets.
Forward Purchase Contract	Forward Purchase Contract In late 2011, Private Histogen contracted for research services from EPS Global Research Pte. Ltd. (“EPS”) to conduct clinical trials and compile data from a study that took place in 2011 and 2013. The unpaid amount due for the services was approximately $0.3 million. On January 26, 2017, Private Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby Private Histogen paid $50,000 and issued EPS 14,342 shares of Series D convertible preferred stock. The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $0.3 million at September 30, 2020 and December 31, 2019, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. The Company has the sole option to initiate the timing of the repurchase of the shares (which were converted into shares of common stock upon the Merger) before the deadline date. The Settlement Agreement was treated as debt subject to Accounting Standards Codification (“ASC”) 470, Debt Distinguishing Liabilities from Equity The Company determined the fair value of the liability to be approximately $0.3 million which is the value as if the repurchase commitment was exercised immediately. As of September 30, 2020 and December 31, 2019, the fair value of the EPS forward contract remained at approximately $0.3 million and is included in other liabilities in the accompanying condensed consolidated balance sheets.
Convertible Preferred Stock	Convertible Preferred Stock Prior to the Merger, Private Histogen had shares of convertible preferred stock outstanding that were conditionally redeemable, as the redemption rights were either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control, and were classified as temporary equity.
Comprehensive Income (Loss)	Comprehensive Income (Loss) The Company is required to report all components of comprehensive income (loss), including net income (loss), in the accompanying condensed consolidated financial statements in the period in which they are recognized. Comprehensive income (loss) is defined as the change in equity during a period from transactions and other events and circumstances from non-owner	Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the consolidated financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner
Revenue Recognition	Revenue Recognition Product and License Revenue The Company records revenue in accordance with ASC 606, Revenue from Contracts with Customers Grant Awards In March 2017, the National Science Foundation (“NSF”), a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange 958-605, Not-for-Profit In September 2020, the Company was approved for a grant award from the U.S. Department of Defense (“DoD”) in the amount of approximately $2.0 million to partially fund the Company’s planned Phase 1/2 clinical trial of HST-003 Professional Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable.
Cost of Product Revenue	Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition.
Cost of Professional Services Revenue	Cost of Professional Services Revenue Cost of professional services revenue represents the Company’s costs for full-time employee equivalents and actual out-of-pocket
Research and Development Expenses	Research and Development Expenses All research and development costs are charged to expense as incurred. Research and development expenses primarily include (i) payroll and related costs associated with research and development performed, (ii) costs related to clinical and preclinical testing of the Company’s technologies under development, and (iii) other research and development costs including allocations of facility costs.	Research and Development Expenses All research and development costs are charged to expense as incurred. Research and development expenses primarily include (i) payroll and related costs associated with research and development performed, (ii) costs related to clinical and preclinical testing of the Company’s technologies under development, and (iii) other research and development including allocations of facility costs.
Acquired In-Process Research and Development Expense	Acquired In-Process The Company has acquired and may continue to acquire the rights to drug candidates in various stages of development. The up-front in-process
General and Administrative Expenses	General and Administrative Expenses General and administrative expenses represent personnel costs for employees involved in general corporate functions, including finance, accounting, legal and human resources, among others. Additional costs included in general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, charitable contributions, recruiting, allocated facility and general information technology costs, depreciation and amortization, and other general corporate overhead expenses.
Patent Costs	Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying condensed consolidated statements of operations.	Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included in general and administrative expenses in the accompanying consolidated statements of operations.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income taxes are recorded for temporary differences between consolidated financial statement carrying amounts and the tax basis of assets and liabilities. Deferred tax assets and liabilities reflect the tax rates expected to be in effect for the years in which the differences are expected to reverse. No income tax expense or benefit was recorded for the three and nine months ended September 30, 2020 and 2019, due to the full valuation allowance on the Company’s net deferred tax assets. A valuation allowance is provided if it is more likely than not that some or all the deferred tax assets will not be realized. The Company also follows the provisions of accounting for uncertainty in income taxes which prescribes a model for the recognition and measurement of a tax position taken or expected to be taken in a tax return, and provides guidance on derecognition, classification, interest and penalties, disclosure and transition. The Company’s policy is to recognize interest or penalties related to income tax matters in income tax expense. Interest and penalties related to income tax matters were not material for the periods presented.	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income taxes are recorded for temporary differences between consolidated financial statement carrying amounts and the tax basis of assets and liabilities. Deferred tax assets and liabilities reflect the tax rates expected to be in effect for the years in which the differences are expected to reverse. A valuation allowance is provided if it is more likely than not that some or all the deferred tax assets will not be realized. The Company also follows the provisions of accounting for uncertainty in income taxes which prescribes a model for the recognition and measurement of a tax position taken or expected to be taken in a tax return, and provides guidance on derecognition, classification, interest and penalties, disclosure and transition. The Company’s policy is to recognize interest or penalties related to income tax matters in income tax expense. Interest and penalties related to income tax matters were not material for the periods presented.
Net Loss Per Share	Net Loss Per Share Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For the three and nine months ended September 30, 2020 and 2019, diluted net loss per share attributable to common stockholders is equal to basic net loss per share attributable to common stockholders as common stock equivalent shares from stock options and convertible preferred stock were anti-dilutive. The following table sets forth outstanding potentially dilutive shares that have been excluded from the calculation of diluted net loss per share attributable to common stockholders because of their anti-dilutive effect (in common stock equivalents): September 30, September 30, Outstanding stock options 1,499,123 1,358,588 Convertible preferred stock — 5,046,213 Warrants to purchase common stock 4,929 3,585 Warrants to purchase convertible preferred stock — 107,565 Total 1,504,052 6,515,951	Net Loss Per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. The calculation for net loss per share gives effect to the dilutive securities under the treasury stock method. For the years ended December 31, 2019 and 2018, there is no difference in the number of shares used to compute basic and diluted net loss per share due to the Company’s net loss position. The following table sets forth potentially dilutive shares that have been excluded from the calculation of net loss per share because of their anti-dilutive effect: Years Ended December 31, 2019 2018 Common stock options issued and outstanding 9,497,923 6,150,000 Shares issuable upon conversion of convertible preferred stock 35,184,882 33,561,102 Warrants to purchase common stock 25,000 25,000 Warrants to purchase convertible preferred stock — 950,000 Total anti-dilutive shares 44,707,805 40,686,102
Common Stock Valuations	Common Stock Valuations Prior to the Merger, the Company was required to periodically estimate the fair value of common stock with the assistance of an independent third-party valuation expert when issuing stock options and computing its estimated stock-based compensation expense. The assumptions underlying these valuations represented management’s best estimates, which involved inherent uncertainties and the application of significant levels of management judgment. In order to determine the fair value, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving various liquidity events; the lack of marketability of the Company’s common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions.
Stock-Based Compensation	Stock-Based Compensation Stock Options The Company recognizes stock-based compensation expense over the requisite service period on a straight-line basis. Employee and director stock-based compensation for stock options is measured based on estimated fair value as of the grant date, using the Black-Scholes option pricing model, in calculating the fair value of option grants as of the grant date. The Company uses the following assumptions for estimating fair value of option grants: Fair Value of Common Stock Expected Volatility Expected Term Risk-Free Interest Rate zero-coupon Expected Forfeiture Rate Performance-Based Options Stock-based compensation expense for performance-based options is recognized based on amortizing the fair market value as of the grant date over the periods during which the achievement of the performance is probable. Performance-based options require certain performance conditions to be achieved in order for these options to vest. These options vest on the date of achievement of the performance condition. Market-Based Options Stock-based compensation expense for market-based options is recognized on a straight-line basis over the derived service period, regardless of whether the market condition is satisfied. Market-based options subject to market-based performance targets require achievement of the performance target in order for these options to vest. The Company estimates the fair value of market-based options as of the grant date and expected term using a Monte Carlo simulation that incorporates option-pricing inputs covering the period from the grant date through the end of the derived service period. The expected volatility as of the grant date is estimated and based on the historical volatility of a group of similar companies that are publicly traded. The risk-free interest rate is based on the yield on zero-coupon
Recent Accounting Pronouncements	Recently Issued Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12 , Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes 2019-12”). 2019-12 2019-12 2019-12 Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments Credit Losses (Topic 326): Measurements of Credit Losses on Financial Instruments 2016-13”), available-for-sale ASU 2016-13 ASU 2016-13 In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement 2018-13”). 2018-13 2018-13 2018-13	Recently Issued Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. In June 2016, the FASB issued ASU 2016-13, Financial Instruments Credit Losses (Topic 326): Measurements of Credit Losses on Financial Instruments available-for-sale 2016-13 In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value non-public 2018-13 In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In January 2020, the FASB issued ASU 2020-01, Investments – Equity Securities (Topic 321), Investments – Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) – Clarifying the Interactions between Topic 321, Topic 323, and Topic 815 (a consensus of the Emerging Issues Task Force)
Basis of Presentation and Principles of Consolidation		Basis of Presentation and Principles of Consolidation The consolidated financial statements include the accounts of the Company and its controlled subsidiaries and have been prepared in accordance with U.S. GAAP. All intercompany balances and transactions have been eliminated upon consolidation. The Company acquired Centro De Investigacion de Medicina Regenerativa, S.A. de C.V. (“CIMRESA”), a company in Mexico, during 2018 to facilitate a potential clinical development program for HSC. This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to FDA). CIMRESA has no operational or financial activity for the years ended December 31, 2019 and 2018. The Company holds an interest in Adaptive Biologix, Inc. (“AB”, formerly Histogen Oncology, LLC). AB was formed to develop and market applications for the treatment of cancer. The Company consolidates AB into its consolidated financial statements.
Joint Venture and Variable Interest Entities		Joint Venture and Variable Interest Entities The Company determined that AB is a variable interest entity (“VIE”) and that Histogen is its primary beneficiary. The Company holds greater than 50% of the shares and has the authority to manage the business and affairs of the VIE. AB’s other shareholder does not have a controlling interest. On January 12, 2018, AB was converted into a traditional C corporation, a Delaware corporation, under a Plan of Conversion agreement between the Company and the other member of the limited liability company, Wylde, LLC (“Wylde”). The entity structure change eliminated some of the special rights Wylde had under the LLC charter and gave the Company more control over the voting rights under the new corporate structure. The Plan of Conversion called for 3,800,000 common stock shares of AB to be issued to the Company and Wylde in proportion to their interest in the LLC immediately before the agreement was executed. Contemporaneously, the Company offered to purchase, and Wylde agreed to sell, 100,000 of the AB common shares for $1.00 per share for a total price of $100 thousand. The completion of this transaction among the stockholders of AB resulted in Histogen owning 2,600,000 common shares or approximately 68%. A VIE is typically an entity for which the Company has less than a 100% equity interest but controls the decision making over the business and affairs of the entity, directs the decisions driving the economic performance of such entity and participates in the profit and losses of such an entity. The Company weighed both quantitative and qualitative information about the different risks and reward characteristics of each entity and the significance of that entity to the consolidating group in the aggregate.
Reclassifications		Reclassifications Certain prior period amounts have been reclassified to conform to the current period presentation. These reclassifications had no effect on previously reported net loss, Stockholders’ deficit or cash flows from operating activities.
Concentrations		Concentrations Credit Risk The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institutions in which those deposits are held. Customer Risk For the years ended December 31, 2019 and 2018, one customer accounted for revenues of approximately $10.5 million, or 91% of total revenue, and $860 thousand, or 48% of total revenue, respectively. The accounts receivable balance of the customer was approximately $11 thousand and $21 thousand as of December 31, 2019 and 2018, respectively.
Accounts Receivable		Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. The allowance is based on an analysis of historical bad debt, current receivables aging and expected future write-offs of uncollectible accounts, as well as an assessment of specific identifiable accounts considered at risk or uncollectible. Additions to the allowance for doubtful accounts include provisions for bad debt and deductions from the allowance for doubtful accounts include customer write-offs. Allowance for doubtful accounts was $0 and approximately $22 thousand as of December 31, 2019 and 2018, respectively.
Valuation of Long-Lived Assets		Valuation of Long-Lived Assets Long-lived assets to be held and used, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. The Company has not recognized any impairment to long-lived assets through December 31, 2019.
Warrant Liabilities for Convertible Preferred Stock		Warrant Liabilities for Convertible Preferred Stock The Company accounts for freestanding warrant instruments that either conditionally or unconditionally obligate the issuer to transfer redeemable stock as liabilities regardless of the timing of the redemption feature or price, even though the underlying shares may be classified as permanent or temporary equity. Since the Company’s convertible preferred stock is contingently redeemable, the warrants to purchase shares of convertible preferred stock are accounted for as liabilities. The Company estimates the fair values of the warrants using the Black-Scholes option pricing model. The liabilities for warrants to purchase the convertible preferred stock is remeasured at each balance sheet date with changes to fair value being recognized as a component of other income (expense) in the consolidated statements of operations. As of December 31, 2019, the warrant liabilities for convertible preferred stock expired unexercised and are no longer outstanding.
Indemnification Liability		Indemnification Liability The Company estimates the fair value of the indemnification liability using the fair value of the Series B preferred stock and the estimated fair value of the Company’s common stock price at the end of each period. Any resulting increase or decrease in estimated fair value is recorded as a component of other income (expense) in the consolidated statements of operations. In January 2019, the indemnification liability was settled. See Note 20 – Related Parties for further information.
Fair Value Measurements		Fair Value Measurements ASC 820, Fair Value Measurements • Level 1 — Observable inputs such as quoted price (unadjusted) for identical instruments in active markets. • Level 2 — Observable inputs such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model derived valuations whose significant inputs are observable. • Level 3 — Unobservable inputs that reflect the reporting entity’s own assumptions. As of December 31, 2019, the Company did not have any assets or liabilities measured at fair value on its consolidated balance sheet. The following table presents the Company’s fair value hierarchy for its liabilities measured at fair value as of December 31, 2018 (in thousands): Fair Value Measurements at December 31, Quoted Prices Significant Other Significant Indemnification liability $ 239 $ — $ — $ 239 Warrant liabilities 276 — — 276 Total fair value $ 515 $ — $ — $ 515 The change in the liabilities measured at fair value using Level 3 unobservable inputs is as follows (in thousands): Indemnification Warrant Balance at December 31, 2017 $ — $ 229 Issuance 182 — Change in fair value 57 47 Balance at December 31, 2018 $ 239 $ 276 Change in fair value — (276 ) Settlement (239 ) — Balance at December 31, 2019 $ — $ — The following inputs were used in determining the fair value of the indemnification and warrant liabilities valued using the Black-Scholes-Merton option pricing model: December 31, 2018 Expected volatility 59.0 % Risk-free interest rate 2.6 % Expected term (in years) 1.0 Expected dividend yield 0.0 %
Convertible Preferred Stock		Convertible Preferred Stock Convertible preferred stock subject to mandatory redemption is classified as a liability and measured at fair value and is included as a component of other liabilities in the accompanying consolidated balance sheets. See Note 11 – Forward Purchase Contract for further information. Convertible preferred stock that is conditionally redeemable (including preferred stock that has redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) is classified as temporary equity.
Revenue Recognition		Revenue Recognition Product and License Revenue The Company records revenue in accordance with ASC 606, Revenue from Contracts with Customers Grant Revenue In March 2017, the National Science Foundation (“NSF”), a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange 958-605, Not-for-Profit Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable. Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition, including write-offs of inventory. Cost of Professional Services Revenue Cost of professional services revenue represents the Company’s costs for full-time employee equivalents (“FTE”) and actual out-of-pocket
Acquired In-Process Research and Development Expense		Acquired In-Process The Company has acquired and may continue to acquire the rights to drug candidates in various stages of development. The up-front in-process
General and Administrative Expenses		General and Administrative Expenses General and administrative expenses represent personnel costs for employees involved in general corporate functions, including finance, accounting, legal and human resources, among others. Additional costs included in general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, charitable contributions, recruiting, allocated facility and general information technology costs, depreciation and amortization, and other general corporate overhead expenses.
Common Stock Valuations		Common Stock Valuations The Company is required to periodically estimate the fair value of common stock when issuing stock options and computing its estimated stock-based compensation expense. The fair value of common stock was determined on a periodic basis, with the assistance of an independent third-party valuation expert. The assumptions underlying these valuations represented management’s best estimates, which involved inherent uncertainties and the application of significant levels of management judgment. The fair value of the common stock underlying the Company’s stock options was estimated at each grant date. The Company’s Board of Directors intended all options granted to be exercisable at a price per share not less than the estimated per share fair value of common stock underlying those options on the date of grant. In order to determine the fair value, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving a liquidity event, such as an initial public offering, or IPO, or sale, given prevailing market conditions; the lack of marketability of the Company’s common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions.
Stock-Based Compensation		Stock-Based Compensation Pursuant to ASC 718, Stock Compensation, The Company estimates the fair value of stock option awards to employees, directors and non-employees non-employee zero-coupon
Recently Adopted Accounting Pronouncements		Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) Leases 2018-11, Leases (Topic 842): Targeted Improvements 2016-02 use-of-hindsight
Predecessor Company [Member]
Use of Estimates		Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Segment Reporting		Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is used in making decisions regarding resource allocation and assessing performance. To date, the Company has viewed its operations and managed its business as one segment operating primarily in the United States.
Property and Equipment		Property and Equipment Property and equipment, which consisted of furniture and fixtures, computers and office equipment, scientific equipment and leasehold improvements, were stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements were amortized over the shorter of their estimated useful lives or the lease term.
Long-Lived Assets		Long-Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objective. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset’s fair value. Through December 31, 2019, the Company has recognized $50,000 in impairment losses.
Comprehensive Income (Loss)		Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from nonowner sources, including unrealized gains and losses on marketable securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented.
Revenue Recognition		Revenue Recognition Under the relevant accounting literature, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. The Company performs the following five steps in order to determine revenue recognition for contracts: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, the entity satisfies a performance obligation. At contract inception, the Company identifies the performance obligations in the contract by assessing whether the goods or services promised within each contract are distinct. Revenue is then recognized for the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. In a contract with multiple performance obligations, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation, which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price(s) may include estimates regarding forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. Any change made to estimated progress towards completion of a performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in a contract, the Company recognizes revenues from the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from the allocated transaction price. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue or expense recognition as a change in estimate. At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being reached. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or a collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates catch-up For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, and a license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, the Company has not recognized any royalty revenue from collaborative arrangements. In December 2016, the Company entered into an Option, Collaboration and License Agreement (the Collaboration Agreement) and an Investment Agreement (the Investment Agreement) with Novartis Pharma AG (Novartis). The Company concluded that there were two significant performance obligations under the Collaboration Agreement: the license and the research and development services, but that the license is not distinct from the research and development services as Novartis cannot obtain value from the license without the research and development services, which the Company is uniquely able to perform. The Company concluded that progress towards completion of the performance obligations related to the Collaboration Agreement is best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The Company periodically reviews and updates the estimated collaboration expenses, when appropriate, which adjusts the percentage of revenue that is recognized for the period. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in the period could be materially impacted. The transaction price to be recognized as revenue under the Collaboration Agreement consists of the upfront payment, option exercise fee, deemed revenue from the premium paid by Novartis under the Investment Agreement and estimated reimbursable research and development costs. Certain expenses directly related to execution of the Collaboration Agreement were capitalized as assets on the balance sheet and are being expensed in a manner consistent with the methodology used for recognizing revenue. The Collaboration Agreement was terminated, effective September 30, 2019, and the Company will not receive any future milestone, royalty or profit and loss sharing payments under the Collaboration Agreement. See Note 9 – Collaboration and License Agreements for further information.
Research and Development Expenses		Research and Development Expenses All research and development costs are expensed as incurred.
Income Taxes		Income Taxes The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. As of December 31, 2019, there are no unrecognized tax benefits included in the balance sheet that would, if recognized, affect the Company’s effective tax rate. The Company has not recognized interest and penalties in the balance sheets or statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2019, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities.
Net Loss Per Share		Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common share equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities have been excluded from the computation of diluted net loss per share in the periods in which they would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to compute basic and diluted shares outstanding due to the Company’s net loss position. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in thousands): December 31, 2019 2018 2017 Warrants to purchase common stock 1 1 15 Common stock options issued and outstanding 130 539 482 RSUs outstanding 145 — — Shares issuable upon conversion of convertible note payable — — 296 Total 276 540 793
Stock-Based Compensation		Stock-Based Compensation Stock-based compensation expense for stock option grants and restricted stock units (RSUs) under the Company’s equity plans is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period of the stock-based award, and forfeitures are recognized as they occur. Stock-based compensation expense for employee stock purchases under the Company’s 2013 Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month The fair value of stock options is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method. The expected volatility of stock options is based upon the historical volatility of the Company and a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2019 2018 2017 Assumptions Risk-free interest rate 1.82% - 2.50 % 2.55% - 3.03 % 1.83% - 2.13 % Expected dividend yield 0 % 0 % 0 % Expected volatility 105% - 119 % 94% - 100 % 93% - 97 % Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1
Recent Accounting Pronouncements		Recent Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, 2016-02 right-of-use 2016-02, non-lease See Note 11 – Commitments for further information.
Concentrations		Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash. Additionally, the Company established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity.
Fair Value Measurements		Fair Value of Financial Instruments The carrying amounts of collaboration receivables, prepaid and other current assets, and accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items.
Cash and Cash Equivalents		Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts.
Marketable Securities		Marketable Securities The Company classifies its marketable securities as available-for-sale At each balance sheet date, the Company assesses available-for-sale

Description of Business, Basi_3

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share	The following table sets forth outstanding potentially dilutive shares that have been excluded from the calculation of diluted net loss per share attributable to common stockholders because of their anti-dilutive effect (in common stock equivalents): September 30, September 30, Outstanding stock options 1,499,123 1,358,588 Convertible preferred stock — 5,046,213 Warrants to purchase common stock 4,929 3,585 Warrants to purchase convertible preferred stock — 107,565 Total 1,504,052 6,515,951	The following table sets forth potentially dilutive shares that have been excluded from the calculation of net loss per share because of their anti-dilutive effect: Years Ended December 31, 2019 2018 Common stock options issued and outstanding 9,497,923 6,150,000 Shares issuable upon conversion of convertible preferred stock 35,184,882 33,561,102 Warrants to purchase common stock 25,000 25,000 Warrants to purchase convertible preferred stock — 950,000 Total anti-dilutive shares 44,707,805 40,686,102
Predecessor Company [Member]
Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share		The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in thousands): December 31, 2019 2018 2017 Warrants to purchase common stock 1 1 15 Common stock options issued and outstanding 130 539 482 RSUs outstanding 145 — — Shares issuable upon conversion of convertible note payable — — 296 Total 276 540 793

Inventories (Tables)

Inventories (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Components of Inventories	Inventories consisted of the following (in thousands): September 30, 2020 December 31, 2019 Raw materials $ 116 $ 106 Work in process 337 — Total $ 453 $ 106	Inventories consisted of the following components (in thousands): December 31, 2019 2018 Raw materials $ 106 $ 98 Work in process — 841 Finished goods — — Inventories $ 106 $ 939

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Schedule of Property and Equipment	Property and equipment, net consisted of the following (in thousands): September 30, 2020 December 31, 2019 Lab and manufacturing equipment $ 1,235 $ 1,231 Leasehold improvements 845 845 Office furniture and equipment 157 157 Total 2,237 2,233 Less: accumulated depreciation and amortization (1,942 ) (1,913 ) Property and equipment, net $ 295 $ 320	Property and equipment consisted of the following (in thousands): Years Ended December 31, 2019 2018 Leasehold improvements $ 845 $ 840 Lab and manufacturing equipment 1,231 1,084 Office furniture and equipment 157 131 Total 2,233 2,055 Less: accumulated depreciation and amortization (1,913 ) (1,768 ) Property and equipment, net $ 320 $ 287
Predecessor Company [Member]
Schedule of Property and Equipment		Property and equipment consist of the following (in thousands): December 31, 2019 2018 Furniture and fixtures $ — $ 334 Equipment — 208 Leasehold improvements — 147 — 689 Less accumulated depreciation and amortization — (535 ) Total $ — $ 154

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Prepaid and Other Current Assets	Prepaid and other current assets consisted of the following (in thousands): September 30, 2020 December 31, 2019 Insurance $ 466 $ — Security deposit 81 — Clinical research 13 50 Other 139 117 Total $ 699 $ 167
Summary of Other Assets	Other assets consisted of the following (in thousands): September 30, 2020 December 31, 2019 Insurance $ 1,016 $ — Other 75 69 Total $ 1,091 $ 69
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Current portion of finance lease liabilities $ 8 $ 6 Compensation 272 182 Clinical trial and study related costs 161 22 Legal fees 2 169 Other 110 67 Total $ 553 $ 446
Summary of Other Liabilities	Other liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Noncurrent portion of finance lease liabilities $ 25 $ 31 Forward purchase contract 290 290 Total $ 315 $ 321
Summary of Accrued Labilities and Other Liabilities		Accrued liabilities consist of the following (in thousands): December 31, December 31, Current portion of notes payable – related party $ — $ 7 Accrued interest – related party — 2 Current portion of finance lease liabilities 6 25 Accrued compensation 182 86 Other 258 546 Total $ 446 $ 666 Other liabilities consist of the following (in thousands): December 31, December 31, Noncurrent portion of finance lease liabilities $ 31 $ 7 Forward purchase contract 290 290 Noncurrent portion of deferred rent — 89 Total $ 321 $ 386

Merger (Tables)

Merger (Tables)	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Summary of Purchase Price Paid in Merger	The total purchase price paid in the Merger has been allocated to the net assets acquired and liabilities assumed based on their fair values as of the completion of the Merger. The following summarizes the purchase price paid in the Merger (in thousands, except share and per share amounts): Number of shares of the combined organization owned by the Company’s pre-Merger 3,394,299 Multiplied by the fair value per share of Conatus common stock (1) $ 5.56 Fair value of consideration issued to effect the Merger $ 18,872 Transaction costs 1,817 Purchase price $ 20,689 (1) Based on the last reported sale price of the Company’s common stock on the Nasdaq Capital Market on May 26, 2020, the closing date of the Merger, and gives effect to the Reverse Stock Split.
Summary of Allocation of Purchase Price	The allocation of the purchase price is as follows (in thousands): Cash acquired $ 12,835 Net assets acquired 710 Acquired IPR&D (2) 7,144 Purchase price $ 20,689 (2) Represents the research and development projects of Conatus which were in-process,

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Equity [Abstract]
Summary of Authorized, Issued and Outstanding Shares of Convertible Preferred Stock	The authorized, issued and outstanding shares of convertible preferred stock as of December 31, 2019 consisted of the following: Shares Authorized Shares Issued and Outstanding Liquidation Preference Carrying Value (in thousands) Series A 10,000,000 1,360,547 $ 9,486 $ 9,486 Series B 35,000,000 1,144,567 7,981 9,356 Series C 8,000,000 1,075,637 7,500 5,550 Series D 20,000,000 1,465,403 15,327 14,678 Total 73,000,000 5,046,154 $ 40,294 $ 39,070	The authorized, issued and outstanding shares of convertible preferred stock as of December 31, 2019 consist of the following: Shared Shares Issued and Liquidation Carrying (in thousands) Series A 10,000,000 9,486,575 $ 9,486 $ 9,486 Series B 35,000,000 7,980,620 7,981 9,356 Series C 8,000,000 7,500,000 7,500 5,550 Series D 20,000,000 10,217,687 15,327 14,678 Total 73,000,000 35,184,882 $ 40,294 $ 39,070 The authorized, issued and outstanding shares of convertible preferred stock as of December 31, 2018 consist of the following: Shared Shares Issued and Liquidation Carrying (in thousands) Series A 10,000,000 9,486,575 $ 9,486 $ 9,486 Series B 35,000,000 7,866,175 7,866 9,232 Series C 8,000,000 7,500,000 7,500 5,550 Series D 20,000,000 8,708,352 13,063 12,415 Total 73,000,000 33,561,102 $ 37,915 $ 36,683

Stock-Based Compensation Expe_2

Stock-Based Compensation Expense (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Summary of stock option	The following summarizes activity related to the Company’s stock options under the 2017 Plan and the 2020 Plan for the nine months ended September 30, 2020: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 1,362,173 $ 3.16 6.34 $ 2,926 Granted 124,119 $ 4.61 Exercised (28,684 ) $ 1.40 Cancelled or forfeited (74,576 ) $ 4.30 Outstanding at September 30, 2020 1,383,032 $ 3.26 5.87 $ 528 Vested and exercisable at September 30, 2020 897,647 $ 2.31 4.39 $ 528	The following summarizes activity related to the Company’s stock options under the 2007 Plan and 2017 Plan for the years ended December 31, 2019 and 2018: Options Weighted- Weighted-average Aggregate Outstanding at December 31, 2017 5,730,000 $ 0.17 5.10 $ 2,174 Granted 1,400,000 0.57 Exercised (790,000 ) 0.14 Cancelled / Forfeited (190,000 ) 0.42 Outstanding at December 31, 2018 6,150,000 $ 0.26 5.60 $ 3,098 Granted 3,722,923 0.76 Exercised (250,000 ) 0.14 Cancelled / Forfeited (125,000 ) 0.63 Outstanding at December 31, 2019 9,497,923 $ 0.45 6.34 $ 2,926 Vested and exercisable at December 31, 2019 5,272,552 $ 0.23 4.24 $ 2,814
Schedule of Black-Scholes Option Pricing Model Assumptions	The following assumptions were used to calculate the fair value of awards granted to employees, non-employees Three Months Ended Nine Months Ended 2020 2019 2020 2019 Expected volatility — % 70.0 % 76.3 % 70.0 % Risk-free interest rate — % 1.59 % 0.45 % 2.54 % Expected term (in years) — 6.25 6.25 6.25 Expected dividend yield — — — —	The following inputs were used in determining the fair value of the indemnification and warrant liabilities valued using the Black-Scholes-Merton option pricing model: December 31, 2018 Expected volatility 59.0 % Risk-free interest rate 2.6 % Expected term (in years) 1.0 Expected dividend yield 0.0 %
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs	The compensation cost that has been included in the accompanying condensed consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Three Months Ended Nine Months Ended 2020 2019 2020 2019 Cost of product revenue $ (3 ) $ 9 $ 16 $ 26 Research and development 2 9 8 31 General and administrative 126 97 432 272 Total $ 125 $ 115 $ 456 $ 329	The compensation cost that has been included in the Company’s consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Years Ended December 31, 2019 2018 Cost of product revenues $ 38 $ 25 Research and development 34 54 General and administrative 366 247 Total $ 438 $ 326
Summary of common stock reserved for future issuance		Common stock reserved for future issuance is as follows: December 31, 2019 Common stock warrants 25,000 Convertible preferred stock (if converted) 35,184,882 Common stock options issued and outstanding 9,497,923 Common stock available for issuance under the 2007 Plan — Common stock available for issuance under the 2017 Plan 3,391,412 48,099,217
Share-based Payment Arrangement [Member]
Schedule of Black-Scholes Option Pricing Model Assumptions		The following weighted-average assumptions were used to calculate the fair value of awards granted to employees, directors and non-employees: Years Ended December 31, 2019 2018 Expected volatility 70.0 % 63.9 % Risk-free interest rate 2.5 % 2.8 % Expected option life (in years) 6.25 6.25 Expected dividend yield 0.0 % 0.0 %
Predecessor Company [Member]
Summary of stock option		The following table summarizes the Company’s stock option activity under all stock option plans for the three years ended December 31, 2019 (options in thousands): Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2016 339 $ 51.00 Granted 173 49.10 Exercised (7 ) 13.20 Forfeited/cancelled/expired (22 ) 60.90 Outstanding at December 31, 2017 483 50.50 Granted 94 50.80 Exercised (22 ) 17.10 Forfeited/cancelled/expired (16 ) 48.30 Outstanding at December 31, 2018 539 52.00 Granted 172 18.40 Exercised — — Forfeited/cancelled/expired (581 ) 45.10 Outstanding at December 31, 2019 130 $ 38.21 5.2 Exercisable at December 31, 2019 113 $ 42.91 4.5
Schedule of Black-Scholes Option Pricing Model Assumptions		The fair value of stock options is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method. The expected volatility of stock options is based upon the historical volatility of the Company and a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2019 2018 2017 Assumptions Risk-free interest rate 1.82% - 2.50 % 2.55% - 3.03 % 1.83% - 2.13 % Expected dividend yield 0 % 0 % 0 % Expected volatility 105% - 119 % 94% - 100 % 93% - 97 % Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1

Stockholders' Equity_Deficit (T

Stockholders' Equity/Deficit (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Summary of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance at September 30, 2020 is as follows: Common stock warrants 4,929 Common stock options issued and outstanding 1,499,123 Common stock available for issuance under the 2020 Plan 725,881 Total 2,229,933
Predecessor Company [Member]
Summary of RSU Activity		The following table summarizes the Company’s RSU activity under all equity plans for the three years ended December 31, 2019 (RSUs in thousands): Total RSUs Weighted- Grant Date Balance at December 31, 2018 — $ — Granted 160 3.10 Forfeited (15 ) 3.10 Balance at December 31, 2019 145 $ 3.10
Summary of Common Stock Reserved for Future Issuance		The following shares of common stock were reserved for future issuance at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Warrants to purchase common stock 1 1 Common stock options issued and outstanding 130 539 Common stock authorized for future option grants 395 84 RSUs outstanding 145 — Common stock authorized for the ESPP 49 50 Total 720 674

Commitments (Tables)

Commitments (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Schedule of Future Minimum Payments of Lease Liabilities	Future minimum payments of lease liabilities were as follows (in thousands): Operating Leases Finance Lease 2020 (remaining 3 months) $ 60 $ 3 2021 616 10 2022 757 10 2023 780 10 2024 803 5 Thereafter 6,010 — Total minimum lease payments 9,026 38 Less: imputed interest (4,277 ) (5 ) Total future minimum lease payments 4,749 33 Less: current obligations under leases — (8 ) Noncurrent lease obligations $ 4,749 $ 25
Schedule of Rent Expense		The components of lease expense were as follows (in thousands): Statement of Operations Classification Operating lease cost: Cost of product revenue $ 165 Research and development 245 General and administrative 160 Total operating lease cost 570 Finance lease cost: Amortization of right-of-use Property and equipment, net 25 Interest on lease liabilities Interest expense 5 Total finance lease cost 30
Predecessor Company [Member]
Schedule of Rent Expense		Rent expense was as follows (in thousands): Year Ended December 31, 2019 2018 2017 Operating lease $ 378 $ 378 $ 378 Short-term leases 68 27 — Total $ 446 $ 405 $ 378
Schedule of ROU Assets and Liabilities Related to Lease and First Lease Amendment		As of December 31, 2019, the Company’s ROU assets and liabilities related to the Lease and the First Lease Amendment are as follows (in thousands): ROU assets (included in other assets) $ 221 Current portion of lease liabilities $ 338 Total lease liabilities $ 338
Schedule of Undiscounted Cash Flows for Operating Lease Liabilities Recorded in Balance Sheet		The following table reconciles the undiscounted cash flows to the operating lease liabilities recorded in the balance sheet as of December 31, 2019 (in thousands): Total lease payments $ 351 Present value adjustment (13 ) Total lease liabilities $ 338

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Assets and Liabilities Measured at Fair Value	The following table presents the Company’s fair value hierarchy for its liabilities measured at fair value as of December 31, 2018 (in thousands): Fair Value Measurements at December 31, Quoted Prices Significant Other Significant Indemnification liability $ 239 $ — $ — $ 239 Warrant liabilities 276 — — 276 Total fair value $ 515 $ — $ — $ 515
Predecessor Company [Member]
Summary of Assets and Liabilities Measured at Fair Value	Below is a summary of assets, including cash, cash equivalents and marketable securities, measured at fair value as of December 31, 2019 and 2018 (in thousands): Fair Value Measurements Using December 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 1,870 $ 1,870 $ — $ — Money market funds 18,833 18,833 — — Total $ 20,703 $ 20,703 $ — $ — Fair Value Measurements Using December 31, 2018 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 2,072 $ 2,072 $ — $ — Money market funds 8,000 8,000 — — Corporate debt securities 30,620 — 30,620 — Total $ 40,692 $ 10,072 $ 30,620 $ —

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Liabilities Measured at Fair Value Using Level 3	The change in the liabilities measured at fair value using Level 3 unobservable inputs is as follows (in thousands): Indemnification Warrant Balance at December 31, 2017 $ — $ 229 Issuance 182 — Change in fair value 57 47 Balance at December 31, 2018 $ 239 $ 276 Change in fair value — (276 ) Settlement (239 ) — Balance at December 31, 2019 $ — $ —

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Summary of Lease Assets and Lease Liabilities	The Company’s lease assets and lease liabilities were as follows (in thousands): Balance Sheet Classification December 31, Assets Operating lease Right-of-use $ 95 Finance leases Property and equipment, net 37 Total lease assets $ 132 Liabilities Current Operating lease liability Current portion of lease liability $ 108 Finance lease liabilities Accrued liabilities 6 Total current liabilities 114 Noncurrent Operating lease liability Noncurrent portion of lease liability — Finance lease liabilities Other liabilities 31 Total noncurrent liabilities 31 Total lease liabilities $ 145
Schedule of Future Minimum Payments of Lease Liabilities	Future minimum payments of lease liabilities were as follows (in thousands): Operating Lease Finance Leases 2020 $ 108 $ 10 2021 — 10 2022 — 10 2023 — 10 2024 — 6 Total minimum lease payments 108 46 Less: imputed interest — (9 ) Total future minimum lease payments 108 37 Less: current obligations under leases (108 ) (6 ) Noncurrent lease obligations $ — $ 31
Summary of Supplemental Cash Flow Information Related to Leases	Supplemental cash flow information related to leases were as follows (in thousands): Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating lease $ 570 Operating cash flows from finance leases 5 Financing cash flows from finance leases 25 Right-of-use 619 Right-of-use $ 40

Noncontrolling Interest (Tables

Noncontrolling Interest (Tables)	12 Months Ended
	Dec. 31, 2019
Noncontrolling Interest [Abstract]
Summary of Changes in Company's Ownership	A summary of changes in the Company’s ownership of AB for the years ended December 31, 2019 and 2018 is as follows (in thousands): Years Ended December 31, 2019 2018 Net loss attributable to Histogen, Inc. stockholders $ (2,966 ) $ (6,125 ) Decrease in Histogen, Inc.’s paid-in — (100 ) Change from net loss attributable to Histogen, Inc. stockholders and transfers to noncontrolling interest $ (2,966 ) $ (6,225 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Income Taxes Based On Losses From Operations	The provision for income taxes based on losses from operations consists of the following (in thousands): Years Ended December 31, 2019 2018 Current Federal $ — $ — State (1 ) (1 ) Total (1 ) (1 ) Deferred Federal 736 1,277 State 180 455 Total 916 1,732 Less valuation allowance (916 ) (1,732 ) Income tax expense $ (1 ) $ (1 )
Reconciliation of Statutory Tax Rates and Effective Tax Rates	The reconciliation of income taxes computed using the statutory U.S. income tax rate and the provision (benefit) for income taxes for the years ended December 31, 2019 and 2018, are as follows (in thousands): Years Ended December 31, 2019 2018 Tax computed at federal statutory rate $ (589 ) 21.00 % $ (1,256 ) 21.00 % State tax, net of federal tax benefits (194 ) 6.92 % (392 ) 6.56 % Permanent items 5 (0.18 %) 104 (1.74 %) Tax credits (66 ) 2.35 % (157 ) 2.62 % Tax rate change 0 0.00 % (18 ) 0.31 % Valuation allowance increase 916 (32.65 %) 1,732 (28.74 %) Other (71 ) 2.53 % (12 ) 0.01 % Provision for income taxes $ 1 (0.04 %) $ 1 0.01 %
Components of Company's Deferred Tax Assets	Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2019 2018 Tax loss carryforward $ 10,757 $ 9,986 R&D credits and other tax credits 1,540 1,455 Stock-based compensation 60 71 Other 947 876 Total deferred tax assets 13,304 12,388 Less valuation allowance (13,304 ) (12,388 ) Deferred tax assets, net $ — $ —
Unrecognized Tax Benefits	The following table reconciles the beginning and ending amount of unrecognized tax benefits for the fiscal years ended December 31, 2019 and 2018 (in thousands): Years Ended December 31, 2019 2018 Gross unrecognized tax benefits at the beginning of the year $ — $ — Additions from tax positions taken in the current year 108 — Additions from tax positions taken in prior years 366 — Gross unrecognized tax benefits at end of the year $ 474 $ —
Predecessor Company [Member]
Reconciliation of Statutory Tax Rates and Effective Tax Rates	A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2019, 2018 and 2017 is as follows: December 31, 2019 2018 2017 Statutory rate 21.0 % 21.0 % 34.0 % Valuation allowance 6.1 % (25.2 )% 51.5 % Federal tax rate change — % — % (93.3 )% General business credits (2.9 )% 6.2 % 10.8 % Expiration of stock options (21.4 )% — % — % Other (2.8 )% (2.0 )% (3.0 )% Effective tax rate — % — % — %
Components of Company's Deferred Tax Assets	Significant components of the Company’s deferred tax assets at December 31, 2019 and 2018 are shown below (in thousands): December 31, 2019 2018 Deferred tax assets Net operating loss carryovers $ 35,901 $ 31,135 Research and development tax credits 8,312 8,641 Intangibles 130 379 Stock options 438 2,255 Compensation 47 452 Deferred revenue — 2,642 Other 88 62 Total gross deferred tax assets 44,916 45,566 Deferred tax liabilities Right-of-use 46 — Total net deferred tax assets 44,870 45,566 Less valuation allowance (44,870 ) (45,566 ) Net deferred tax assets $ — $ —
Unrecognized Tax Benefits	The following table summarizes the activity related to the Company’s unrecognized tax benefits (in thousands): 2019 2018 2017 Balance at beginning of year $ 2,221 $ 1,932 $ 1,319 Additions based on tax positions related to the current year — 289 613 Reductions based on tax positions related to prior years (80 ) — — Balance at end of year $ 2,141 $ 2,221 $ 1,932

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Summary of Investments in Marketable Securities	The Company invests its excess cash in money market funds and debt instruments of financial institutions, corporations, government sponsored entities and municipalities. The Company had no investments in marketable securities at December 31, 2019, the following tables summarize the Company’s investments in marketable securities at December 31, 2018 (in thousands): As of December 31, 2018 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 29,144 $ — $ (17 ) $ 29,127 Total $ 29,144 $ — $ (17 ) $ 29,127

Collaboration and License Agr_2

Collaboration and License Agreements (Tables) - Predecessor Company [Member]	12 Months Ended
	Dec. 31, 2019
Summary of Reconciliation of Deferred Revenue Related to Collaboration Agreement	A reconciliation of the opening and closing balances of deferred revenue related to the Collaboration Agreement, which represents the unrecognized balance of the transaction price, is as follows (in thousands): Deferred Revenue Balance at December 31, 2017 $ 26,691 Cumulative effect of adoption of accounting standard 1,299 Additions to deferred revenue 18,486 Revenue recognized (33,586 ) Balance at December 31, 2018 12,890 Additions to deferred revenue 8,826 Revenue recognized (21,716 ) Balance at December 31, 2019 $ —
Summary of Reconciliation of Deferred Costs Related To Collaboration Agreement	A reconciliation of the opening and closing balances of deferred costs related to execution of the Collaboration Agreement is as follows (in thousands): Deferred Costs Balance at December 31, 2017 $ — Cumulative effect of adoption of accounting standard 687 Costs recognized (377 ) Balance at December 31, 2018 310 Costs recognized (310 ) Balance at December 31, 2019 $ —

Quarterly Financial Data (una_2

Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Predecessor Company [Member]
Summary of Quarterly Financial Data	The following tables summarize the unaudited quarterly financial data for the last two fiscal years (in thousands, except per share data): 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 7,024 $ 10,791 $ 3,376 $ 526 Total operating expenses 11,974 11,619 6,759 3,371 Total other income 203 172 130 116 Net loss (4,747 ) (656 ) (3,253 ) (2,729 ) Net loss per share, basic and diluted (1) (1.43 ) (0.20 ) (0.98 ) (0.82 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 9,737 $ 8,774 $ 7,666 $ 7,409 Total operating expenses 14,794 13,331 12,324 11,414 Total other income 39 60 69 99 Net loss (5,018 ) (4,497 ) (4,589 ) (3,906 ) Net loss per share, basic and diluted (1) (1.67 ) (1.49 ) (1.52 ) (1.26 ) (1) Net loss per share is computed independently for each quarter and the full year based upon respective shares outstanding; therefore, the sum of the quarterly net loss per share amounts may not equal the annual amounts reported.

Description of Business, Basi_4

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	May 26, 2020USD ($)	Jan. 28, 2020shares	Jan. 12, 2018USD ($)$ / sharesshares	Jan. 26, 2017USD ($)shares	Jul. 31, 2020USD ($)	Sep. 30, 2020USD ($)shares	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)Segmentshares	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)Segmentshares	Dec. 31, 2018USD ($)shares
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Reverse stock split description								One-for-ten
Reverse stock split conversion ratio	0.01
Accumulated losses						$ (59,194,000)		$ (59,194,000)		$ (43,933,000)
Cash and cash equivalents						6,649,000	$ 3,758,000	6,649,000	$ 3,758,000	$ 2,065,000	$ 3,027,000
Cash and cash equivalents acquired in merger								$ 12,835,000
Number of AB common shares purchased | shares											100,000
Maximum entity ownership percentage required for variable interest entity								100.00%		100.00%
Number of operating segment | Segment								1		1
Impairment to long-lived assets								$ 0		$ 0
EPS unpaid services						$ 300,000		$ 300,000		$ 340,000
Shares issued | shares						0		0		0
Fair value of liability						$ 300,000		$ 300,000		$ 290,000	$ 290,000
Expected contractual term						0 years	6 years 3 months	6 years 3 months	6 years 3 months		1 year
One Customer [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer						$ 100,000		$ 100,000		100,000
Settlement Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash paid				$ 50,000
Share repurchases, value						$ 300,000		$ 300,000		$ 290,000
Share repurchases, description								The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $0.3 million at September 30, 2020 and December 31, 2019, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. The Company has the sole option to initiate the timing of the repurchase of the shares (which were converted into shares of common stock upon the Merger) before the deadline date.		The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $290 thousand, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. Histogen has the sole option to initiate the timing of the repurchase of the shares before the deadline date.
Gain (Loss) on extinguishment of the original liability				$ 0
Series D Convertible Preferred Stock [Member] | Settlement Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Shares issued | shares				14,342
Maximum [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets								5 years		5 years
Expected contractual term								10 years
Revenue Benchmark [Member] | Customer Concentration Risk [Member] | One Customer [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of revenues						100.00%	39.00%	100.00%	94.00%	91.00%	48.00%
US Department Of Defense [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Grant funding obtained						$ 2,000,000		$ 2,000,000
Grant award expiration period								2025-09
Qualifying expenses incurred						0		$ 0
Reduction of research and development expenses related to award						0		0
Amount reimbursed under terms of award						$ 0		0
Merger [Member] | Conatus [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents acquired in merger	$ 12,800,000
Variable Interest Entity ("VIE")
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, ownership percentage			68.00%							50.00%
Variable interest entity common stock shares owned | $ / shares			$ 2,600,000
Variable Interest Entity ("VIE") | Plan of Conversion Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of common shares specified in Plan of Conversion | shares			3,800,000
Number of AB common shares purchased | shares			100,000
Price per Share Purchase Price of AB common shares			$ 1
Aggregate Purchase Price of AB common shares | $ / shares			$ 100,000
Common Stock Purchase Agreement with Lincoln Park [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Common stock shares maximum committed purchase amount					$ 10,000,000
Remaining available for sale common stock shares maximum committed purchase amount					$ 8,500,000			$ 8,500,000
Long-term purchase commitment, period					24 months
Private Histogen [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Exchange Ratio in reverse merger | shares		0.14342
Histogen stockholders' ownership interests post Merger		71.30%

Description of Business, Basi_5

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Shares Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	1,504,052	6,515,951	44,707,805	40,686,102
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	1,499,123	1,358,588
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		5,046,213	35,184,882	33,561,102
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	4,929	3,585	25,000	25,000
Warrants to Purchase Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		107,565		950,000

Inventories - Components of Inv

Inventories - Components of Inventories (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 116	$ 106	$ 98
Work in process	337		841
Inventories	$ 453	$ 106	$ 939

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Write-off of inventory	$ 186,000	$ 155,000
Inventory, Finished goods	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Property and equipment, gross	$ 2,237	$ 2,233	$ 2,055
Less accumulated depreciation and amortization	(1,942)	(1,913)	(1,768)
Property and equipment, net	295	320	287
Lab and Manufacturing Equipment [Member]
Property and equipment, gross	1,235	1,231	1,084
Leasehold improvements [Member]
Property and equipment, gross	845	845	840
Office Furniture And Equipment [Member]
Property and equipment, gross	$ 157	$ 157	131
Predecessor Company [Member]
Property and equipment, gross			689
Less accumulated depreciation and amortization			(535)
Property and equipment, net			154
Predecessor Company [Member] | Leasehold improvements [Member]
Property and equipment, gross			147
Predecessor Company [Member] | Equipment [Member]
Property and equipment, gross			208
Predecessor Company [Member] | Furniture and fixtures [Member]
Property and equipment, gross			$ 334

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 24	$ 40	$ 74	$ 107	$ 145	$ 150
Predecessor Company [Member]
Property, Plant and Equipment [Line Items]
Depreciation					73	$ 91	$ 108
Net book value of property and equipment written off					$ 100

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Prepaid and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Insurance	$ 466
Security deposit	81
Clinical research	13	$ 50
Other	139	117
Total	$ 699	$ 167

Balance Sheet Details - Summa_2

Balance Sheet Details - Summary of Other Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Insurance	$ 1,016
Other	75	$ 69
Total	$ 1,091	$ 69

Balance Sheet Details - Summa_3

Balance Sheet Details - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Current portion of notes payable - related party			$ 7
Accrued interest - related party			2
Current portion of finance lease liabilities	$ 8	$ 6	25
Accrued compensation	272	182	86
Clinical trial and study related costs	161	22
Other		258	546
Legal fees	2	169
Other	110	67
Total	$ 553	$ 446	$ 666

Balance Sheet Details - Summa_4

Balance Sheet Details - Summary of Other Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Noncurrent portion of finance lease liabilities	$ 25	$ 31	$ 7
Forward purchase contract	290	290	290
Noncurrent portion of deferred rent			89
Total	$ 315	$ 321	$ 386

Revenues - Additional Informati

Revenues - Additional Information (Detail)	Sep. 30, 2016USD ($)shares	Aug. 10, 2016USD ($)	Jan. 31, 2020USD ($)kg	Mar. 31, 2019USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2020USD ($)shares	Sep. 30, 2019USD ($)shares	Sep. 30, 2020USD ($)shares	Sep. 30, 2019USD ($)shares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Disaggregation of Revenue [Line Items]
Revenue						$ 495,000	$ 314,000	$ 1,581,000	$ 9,893,000	$ 11,454,000	$ 1,777,000
Convertible Preferred Stock Series D [Member]
Disaggregation of Revenue [Line Items]
Convertible preferred stock issued | shares									49,144	1,509,335	1,742,167
Common Stock [Member]
Disaggregation of Revenue [Line Items]
Stock issued during the period | shares						675,480	16,158	675,480	21,885	152,594
Previously Reported [Member] | Convertible Preferred Stock Series D [Member]
Disaggregation of Revenue [Line Items]
Convertible preferred stock issued | shares										342,668	1,400,500
Pineworld Capital Limited [Member] | Convertible Preferred Stock Series D [Member]
Disaggregation of Revenue [Line Items]
Convertible preferred stock issued | shares	4,000,000
Pineworld Capital Limited [Member] | Common Stock [Member]
Disaggregation of Revenue [Line Items]
Stock issued during the period | shares	190,377
Pineworld Capital Limited [Member] | License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Milestone revenue recognized										$ 0	$ 0
Royalty revenue										$ 0	0
Pineworld Capital Limited [Member] | License and Supply Agreement [Member] | First Milestone Payment Upon approval of IND by CFDA [Member]
Disaggregation of Revenue [Line Items]
Development milestone payments		$ 800,000
Pineworld Capital Limited [Member] | License and Supply Agreement [Member] | Second Milestone Payment Upon Completion of all Clinical Trials Required for NDA Filing with CFDA [Member]
Disaggregation of Revenue [Line Items]
Development milestone payments		1,800,000
Pineworld Capital Limited [Member] | License and Supply Agreement [Member] | Third Milestone Payment Upon NDA Filing with CFDA [Member]
Disaggregation of Revenue [Line Items]
Development milestone payments		1,200,000
Pineworld Capital Limited [Member] | License and Supply Agreement [Member] | Fourth Milestone Payment Upon Approval Of NDA by CFDA [Member]
Disaggregation of Revenue [Line Items]
Development milestone payments		1,200,000
Pineworld Capital Limited [Member] | First $50 million of Net Sales of HST-001 | License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Royalty payments, percentage of net sales										4.00%
Pineworld Capital Limited [Member] | Up to $50 million Net Sales of HST-001 | License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Royalty payments, percentage of net sales										5.50%
Pineworld Capital Limited [Member] | up to $125 million Net Sales of HST-001 | License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Royalty payments, percentage of net sales										6.50%
Pineworld Capital Limited [Member] | Above $200 million Net Sales of HST-001 | License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Royalty payments, percentage of net sales										7.50%
Pineworld Capital Limited [Member] | Maximum [Member] | License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Manufacturing costs to be reimbursed	$ 150,000
Development milestone payments		$ 5,000,000
2017 Allergan Agreement [Member]
Disaggregation of Revenue [Line Items]
Cash payment received					$ 11,000,000
Potential additional payments					5,500,000
2019 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
One-time payment				$ 7,500,000
Patent lives expiration period				9 years
Milestone revenue recognized							$ 0		$ 15,000,000
Deferred revenue							800,000		800,000
2019 Allergan Amendment Agreement [Member] | Previously Reported [Member]
Disaggregation of Revenue [Line Items]
Patent lives expiration period				10 years
2020 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue						$ 400,000		$ 400,000
Patent lives expiration period			9 years
Milestone revenue recognized						5,000	5,000	15,000	15,000
Deferred revenue							100,000		100,000
Additional quantity of product to be supplied | kg			200
Up front payment received			$ 1,000,000
CCM Skin Care [Member]
Disaggregation of Revenue [Line Items]
Revenue								100,000		$ 0
Deferred revenue allocated to performance obligation										199,000
CCM Skin Care [Member] | Potential Future Improvements [Member]
Disaggregation of Revenue [Line Items]
Milestone revenue recognized										19,000	19,000
Deferred revenue						100,000		100,000		200,000
CCM Skin Care [Member] | Potential Future Improvements [Member] | Previously Reported [Member]
Disaggregation of Revenue [Line Items]
Deferred revenue										157,000	177,000
Supply of CCM to Allergan [Member]
Disaggregation of Revenue [Line Items]
Deferred revenue										0	1,500,000
Deferred revenue allocated to performance obligation										1,800,000
Recognition of revenue from deferred revenue										1,500,000	292,000
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue						419,000	190,000	419,000	1,956,000	3,415,000	1,254,000
Product [Member] | Edge Systems License and Supply Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue						0	200,000	0	400,000	855,000	618,000
Product [Member] | 2017 Allergan Agreement [Member] | Minimum [Member]
Disaggregation of Revenue [Line Items]
Sales target for additional potential payment payout					$ 60,000,000
Product [Member] | Supply of CCM to Allergan [Member]
Disaggregation of Revenue [Line Items]
Milestone revenue recognized										2,600,000	636,000
License [Member]
Disaggregation of Revenue [Line Items]
Revenue						5,000	5,000	877,000	7,515,000	7,519,000	19,000
License [Member] | 2019 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue								7,500,000
License [Member] | 2020 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue			$ 900,000
Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue						0	0	0	150,000	150,000	300,000
Professional Services Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue						$ 100,000	$ 100,000	$ 300,000	$ 300,000	$ 370,000	$ 204,000

Merger - Additional Information

Merger - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Closing date of Merger	May 26, 2020

Merger - Summary of Purchase Pr

Merger - Summary of Purchase Price Paid in Merger (Detail) $ / shares in Units, $ in Thousands	May 26, 2020USD ($)$ / sharesshares
Asset Acquisition [Abstract]
Number of shares of the combined organization owned by the Company's pre-Merger stockholders | shares	3,394,299
Multiplied by the fair value per share of Conatus common stock | $ / shares	$ 5.56	[1]
Fair value of consideration issued to effect the Merger	$ 18,872
Transaction costs	1,817
Purchase price	$ 20,689
[1]	Based on the last reported sale price of the Company's common stock on the Nasdaq Capital Market on May 26, 2020, the closing date of the Merger, and gives effect to the Reverse Stock Split.

Merger - Summary of Allocation

Merger - Summary of Allocation of Purchase Price (Detail) $ in Thousands	May 26, 2020USD ($)
Asset Acquisition [Abstract]
Cash acquired	$ 12,835
Net assets acquired	710
Acquired IPR&D	7,144	[1]
Purchase price	$ 20,689
[1]	Represents the research and development projects of Conatus which were in-process, but not yet completed. This consists primarily of Conatus' emricasan product candidate. Current accounting standards require that the fair value of IPR&D projects acquired in an asset acquisition with no alternative future use be allocated a portion of the consideration transferred and charged to expense on the acquisition date. The acquired assets did not have outputs or employees.

PUR Settlement_Investment - Add

PUR Settlement/Investment - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended
	Apr. 30, 2019	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Issuance of common stock for Lordship Indemnification		$ 1,337,000	$ 1,337,000	$ 115,000	$ 115,000
In-process Research and development expense			7,144,000	1,750,000
Payment for milestone			0		0	$ 0
Payments for royalties			$ 0		0	0
Development Assets
Loss Contingencies [Line Items]
Issuance of common stock for Lordship Indemnification				1,750,000	1,750,000
Milestone and royalty payment obligations	$ 400,000
Percentage of royalties on net sales	5.00%
In-process Research and development expense				2,270,000	2,270,000
Purchase of net carrying value allocated to in-process research and development costs				$ 500,000	$ 523,000
Development Assets | Product [Member] | Estimated Sales [Member]
Loss Contingencies [Line Items]
Revenue target for milestone achievement	$ 500,000
Development Assets | Commercialization Milestone [Member]
Loss Contingencies [Line Items]
Milestone and royalty payment obligations	400,000
PUR Biologics, LLC [Member]
Loss Contingencies [Line Items]
Upfront cash paid	500,000
Amount forgiven	22,000
Repayments of outstanding payable assumed	$ 23,000
Carrying value of investment						0
Obligation to absorb losses or liabilities of investee or contribute assets to investee						0
Earnings or losses from investments						$ 0
PUR Biologics, LLC [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Interest in an investment in non-marketable equity instruments						50.00%
PUR Biologics, LLC [Member] | Development Assets | Series D Convertible Preferred Stock [Member]
Loss Contingencies [Line Items]
Issuance of common stock for Lordship Indemnification, shares	167,323
Issuance of common stock for Lordship Indemnification	$ 1,750,000
PUR Biologics, LLC [Member] | Development Assets | Series D Convertible Preferred Stock [Member] | Previously Reported [Member]
Loss Contingencies [Line Items]
Issuance of common stock for Lordship Indemnification, shares	1,166,667
PUR Biologics, LLC [Member] | Development Assets | Maximum [Member]
Loss Contingencies [Line Items]
Potential cash payout	$ 6,250,000

Paycheck Protection Program L_2

Paycheck Protection Program Loan - Additional Information (Detail) - Paycheck Protection Program [Member] - USD ($) $ in Millions	Jun. 05, 2020	Jun. 04, 2020	Apr. 30, 2020
Debt Instrument [Line Items]
Loan proceeds received			$ 0.5
Loan forgiveness period	168 days	56 days
Deferral period of principal and interest payments extended term	10 months	6 months
Required amount of payroll expenditures, percentage	60.00%	75.00%
Existing loans maturity period	5 years	2 years

Stockholders' Equity_Deficit -

Stockholders' Equity/Deficit - Additional Information (Detail)

May 26, 2020shares

Jan. 28, 2020USD ($)

Jan. 24, 2019shares

Aug. 02, 2018USD ($)

Aug. 31, 2017shares

Jul. 31, 2020USD ($)$ / sharesshares

May 31, 2020shares

Aug. 31, 2019USD ($)shares

Apr. 30, 2019shares

May 31, 2017USD ($)$ / sharesshares

Jul. 31, 2013$ / sharesshares

Sep. 30, 2020USD ($)Vote$ / sharesshares

Sep. 30, 2019USD ($)$ / sharesshares

Sep. 30, 2020USD ($)Vote$ / sharesshares

Sep. 30, 2019USD ($)$ / sharesshares

Dec. 31, 2019USD ($)$ / sharesshares

Dec. 31, 2018USD ($)$ / sharesshares

Dec. 31, 2017USD ($)$ / sharesshares

Dec. 18, 2017shares

Dec. 31, 2016$ / sharesshares

Class Of Stock [Line Items]

Net proceeds from the issuance of common stock | $

$ 1,337,000

Convertible preferred stock, shares issued

0

0

5,046,154

Stock issued upon conversion | $

$ 39,070,000

Warrants to purchase common stock

4,929

4,929

Stock-based compensation | $

$ 125,000

$ 115,000

$ 456,000

$ 329,000

$ 438,000

$ 326,000

Unrecognized compensation expense | $

1,500,000

$ 1,500,000

Weighted-average vesting term

4 years

General and Administrative [Member]

Class Of Stock [Line Items]

Stock-based compensation | $

$ 126,000

$ 97,000

$ 432,000

$ 272,000

Private Histogen [Member]

Class Of Stock [Line Items]

Convertible preferred stock shares converted into shares of common stock

5,046,154

5,046,154

Stock Options [Member] | Chief Executive Officer [Member]

Class Of Stock [Line Items]

Stock option plans, remaining vesting period

36 months

Stock options issued

485,178

Vesting term

In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months.

In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months.

Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Stock option plans, remaining vesting period

12 months

Number of fully vested options

48,517

Stock option plans, percentage of options vested

25.00%

Vesting term

The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $200.0 million; (3) the date that the market capitalization of the Company exceeds $275.0 million, and; (4) the date that the market capitalization of the Company exceeds $300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination.

The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $200.0 million; (3) the date that the market capitalization of the Company exceeds $275.0 million, and; (4) the date that the market capitalization of the Company exceeds $300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination.

Performance and Market Based Options [Member] | General and Administrative [Member]

Class Of Stock [Line Items]

Stock-based compensation | $

$ 20,000

$ 100,000

Market Condition-Based Options [Member]

Class Of Stock [Line Items]

Unrecognized compensation expense | $

$ 400,000

$ 400,000

Convertible Preferred Stock [Member]

Class Of Stock [Line Items]

Convertible preferred stock, shares issued

0

0

Convertible preferred stock, dividend rate percentage

6.00%

Preferred stock, voting rights description

The holders of each series of preferred stock were entitled to one vote for each share of common stock into which such preferred stock could then be converted; and with respect to such vote, such holders shall have full voting rights and powers equal to the voting rights and powers of the holders of common stock.

Number of vote entitled for each share of common stock | Vote

1

1

Convertible Preferred Stock Series B [Member]

Class Of Stock [Line Items]

Convertible preferred stock, shares issued

16,413

16,413

Convertible preferred stock, liquidation preferences per share | $ / shares

$ 6.97

$ 6.97

Common stock, price per share | $ / shares

$ 1

$ 1

Convertible Preferred Stock Series D [Member]

Class Of Stock [Line Items]

Convertible preferred stock, shares issued

216,468

216,468

Convertible preferred stock, liquidation preferences per share | $ / shares

$ 10.46

$ 10.46

$ 10.46

$ 10.46

1.50

Common stock, price per share | $ / shares

1.50

$ 1.50

Convertible Preferred Stock Series A, B and C [Member]

Class Of Stock [Line Items]

Convertible preferred stock, liquidation preferences per share | $ / shares

6.97

$ 6.97

$ 1

2017 Plan [Member]

Class Of Stock [Line Items]

Number of common stock shares authorized to issue

837,208

Common stock reserved for issuance to employees, nonemployee directors and consultants

326,711

Stock option plans, remaining vesting period

4 years

Expiration period

10 years

Stock options issued

0

2020 Stock Plan [Member]

Class Of Stock [Line Items]

Number of common stock shares authorized to issue

850,000

Expiration period

10 years

Percentage of outstanding shares of common stock

5.00%

Conatus 2013 Plan [Member]

Class Of Stock [Line Items]

Stock options issued

0

Number of fully vested options

116,091

Weighted average exercise price of fully vested options | $ / shares

$ 37.59

Share-based Payment Arrangement, Tranche One [Member] | Stock Options [Member] | Chief Executive Officer [Member]

Class Of Stock [Line Items]

Stock option plans, percentage of options vested

40.00%

Remaining vesting percentage

25.00%

Share-based Payment Arrangement, Tranche One [Member] | Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Stock option plans, percentage of options vested

40.00%

Share-based Payment Arrangement, Tranche Two [Member] | Stock Options [Member] | Chief Executive Officer [Member]

Class Of Stock [Line Items]

Stock option plans, percentage of options vested

60.00%

Share-based Payment Arrangement, Tranche Two [Member] | Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Minimum market capitalization amount required for vesting | $

$ 200,000,000

Share-based Payment Arrangement, Tranche Three [Member] | Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Minimum market capitalization amount required for vesting | $

275,000,000

Sharebased Compensation Award Tranche Four [Member] | Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Minimum market capitalization amount required for vesting | $

$ 300,000,000

Maximum [Member] | Convertible Preferred Stock [Member]

Class Of Stock [Line Items]

Stock conversion ratio

1

Minimum [Member] | Convertible Preferred Stock [Member]

Class Of Stock [Line Items]

Stock issued upon conversion | $

$ 20,000,000

Stock conversion price per share | $ / shares

$ 31.38

$ 31.38

Common Stock [Member]

Class Of Stock [Line Items]

Common stock shares issued

675,480

16,158

675,480

21,885

152,594

Stock issued upon conversion | $

$ 1,000

Warrants to purchase common stock

1,346

1,346

Exercise price of warrant per share | $ / shares

$ 74.30

$ 74.30

$ 23.08

Warrant expiration date

Jul. 3, 2023

Jul. 3, 2023

Jul. 31, 2021

Common Stock [Member] | Maximum [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

3,583

Predecessor Company [Member]

Class Of Stock [Line Items]

Net proceeds from the issuance of common stock | $

$ 30,600,000

$ 30,610,000

Stock issued upon conversion | $

$ 13,729,000

Warrants to purchase common stock

1,000

1,000

Stock-based compensation | $

$ 4,200,000

$ 3,800,000

4,100,000

Unrecognized compensation expense | $

$ 27,000

Weighted-average vesting term

10 months 24 days

Payment for repurchase of common stock | $

$ 11,200,000

$ 11,203,000

Total remaining options available for future grant

395,000

84,000

Stock options granted to purchase common stock

172,000

94,000

173,000

Weighted-average fair value of options granted | $ / shares

$ 18.40

$ 39.30

$ 37.90

Total intrinsic value of stock options exercised | $

$ 0

$ 600,000

$ 300,000

Intrinsic value of options outstanding | $

16,000

Intrinsic value of options exercisable | $

1,000

Predecessor Company [Member] | Employment Inducement Award [Member]

Class Of Stock [Line Items]

Stock options granted to purchase common stock

52,500

Predecessor Company [Member] | Restricted Stock Units (RSUs) [Member]

Class Of Stock [Line Items]

Unrecognized compensation expense | $

$ 2,100,000

Weighted-average vesting term

7 months 6 days

Number of shares granted

160,000

Predecessor Company [Member] | 2006 Plan [Member]

Class Of Stock [Line Items]

Common stock reserved for issuance to employees, nonemployee directors and consultants

103,030

Predecessor Company [Member] | 2013 Plan [Member]

Class Of Stock [Line Items]

Common stock reserved for issuance to employees, nonemployee directors and consultants

100,000

Stock option plans, remaining vesting period

3 years

Expiration period

10 years

Percentage of outstanding shares of common stock

5.00%

Total remaining options available for future grant

395,143

Predecessor Company [Member] | One-Time Option Exchange [Member]

Class Of Stock [Line Items]

Stock options exchange description

The participants received one new RSU for every two stock options tendered for exchange.

Number of stock options exchanged

320,036

Additional stock compensation expense expected service term

1 year

Predecessor Company [Member] | One-Time Option Exchange [Member] | Restricted Stock Units (RSUs) [Member]

Class Of Stock [Line Items]

Stock option plans, remaining vesting period

1 year

Number of shares granted

160,017

Incremental value of the modifications | $

$ 100,000

Predecessor Company [Member] | Share-based Payment Arrangement, Tranche One [Member] | 2013 Plan [Member]

Class Of Stock [Line Items]

Stock option plans, percentage of options vested

25.00%

Predecessor Company [Member] | Employee Stock [Member]

Class Of Stock [Line Items]

Lower fair market value of purchase price share

85.00%

Outstanding liability | $

$ 0

$ 28,936

$ 16,367

Predecessor Company [Member] | 2013 Warrants [Member] | Series B Preferred Stock [Member]

Class Of Stock [Line Items]

Warrant exercisable to purchase shares

1,124,026

Predecessor Company [Member] | 2013 Warrants [Member] | Convertible promissory notes [Member]

Class Of Stock [Line Items]

Warrant expiration date

May 30, 2018

Predecessor Company [Member] | 2013 Warrants [Member] | Convertible promissory notes [Member] | Series B Preferred Stock [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share | $ / shares

$ 0.90

Predecessor Company [Member] | Lender Warrants [Member] | Convertible promissory notes [Member]

Class Of Stock [Line Items]

Warrant expiration date

Jul. 3, 2023

Predecessor Company [Member] | Lender Warrants [Member] | Term Loan One [Member] | Series B Convertible Preferred Stock [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share | $ / shares

$ 0.90

Warrant expiration date

Jul. 3, 2023

Warrant issued

111,112

Predecessor Company [Member] | Maximum [Member] | Employee Stock [Member]

Class Of Stock [Line Items]

Employee stock purchase plan, employees contribution

20.00%

Predecessor Company [Member] | Common Stock [Member]

Class Of Stock [Line Items]

Common stock shares issued

598,000

598,000

Common stock, price per share | $ / shares

$ 55

Shares repurchased and retired under stock purchase agreement

216,863

Shares repurchased and retired price per share | $ / shares

$ 51.70

Common stock issued

1,000

4,000

2,000

Predecessor Company [Member] | Common Stock [Member] | Employee Stock [Member]

Class Of Stock [Line Items]

Common stock issued

536

3,629

2,430

Predecessor Company [Member] | Common Stock [Member] | 2013 Warrants [Member] | Post IPO [Member] | Convertible promissory notes [Member]

Class Of Stock [Line Items]

Warrants exercisable

13,623

Predecessor Company [Member] | Common Stock [Member] | Lender Warrants [Member] | Convertible promissory notes [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share | $ / shares

$ 74.30

Warrants exercisable

1,346

Sales Agreement with Stifel [Member]

Class Of Stock [Line Items]

Number of shares sold under sales agreement

0

Sales Agreement with Stifel [Member] | Maximum [Member]

Class Of Stock [Line Items]

Aggregate value of common shares that can be sold | $

$ 35,000,000

$ 35,000,000

Sales Agreement with Stifel [Member] | Predecessor Company [Member]

Class Of Stock [Line Items]

Number of shares sold under sales agreement

0

Sales Agreement with Stifel [Member] | Predecessor Company [Member] | Maximum [Member]

Class Of Stock [Line Items]

Common stock, value of shares issued | $

$ 35,000,000

Percentage of commission of gross sales price per share

3.00%

Common Stock Purchase Agreement with Lincoln Park [Member]

Class Of Stock [Line Items]

Aggregate dollar value of share purchase commitment | $

$ 10,000,000

Long-term purchase commitment, period

24 months

Number of common stock shares sold

328,516

280,000

280,000

Sale of common stock price per share | $ / shares

$ 3.04399

Net proceeds from the issuance of common stock | $

$ 1,000,000

$ 300,000

$ 300,000

Remaining available for sale common stock shares maximum committed purchase amount | $

$ 8,500,000

$ 8,500,000

Common stock shares issued

66,964

PUR Settlement [Member] | Convertible Preferred Stock Series D [Member]

Class Of Stock [Line Items]

Convertible preferred stock, shares issued

167,323

167,323

Convertible preferred stock, liquidation preferences per share | $ / shares

$ 10.46

$ 10.46

Stockholders' Equity_Deficit _2

Stockholders' Equity/Deficit - Summary of Authorized, Issued and Outstanding Shares of Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized	0	73,000,000
Shares Issued and Outstanding		5,046,154
Convertible preferred stock, liquidation preference	$ 0	$ 40,294
Carrying Value		$ 39,070
Convertible Preferred Stock Series A [Member]
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		10,000,000
Shares Issued and Outstanding		1,360,547
Convertible preferred stock, liquidation preference		$ 9,486
Carrying Value		$ 9,486
Convertible Preferred Stock Series B [Member]
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		35,000,000
Shares Issued and Outstanding		1,144,567
Convertible preferred stock, liquidation preference		$ 7,981
Carrying Value		$ 9,356
Convertible Preferred Stock Series C [Member]
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		8,000,000
Shares Issued and Outstanding		1,075,637
Convertible preferred stock, liquidation preference		$ 7,500
Carrying Value		$ 5,550
Convertible Preferred Stock Series D [Member]
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		20,000,000
Shares Issued and Outstanding		1,465,403
Convertible preferred stock, liquidation preference		$ 15,327
Carrying Value		$ 14,678

Stockholders' Equity_Deficit _3

Stockholders' Equity/Deficit - Summary of Stock Option Activity (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
2017 and 2020 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Beginning balance	1,362,173
Number of Options, Granted	124,119
Number of Options, Exercised	(28,684)
Number of Options, Cancelled or forfeited	(74,576)
Number of Options, Ending balance	1,383,032	1,362,173
Number of Options, Vested and exercisable	897,647
Weighted-Average Exercise Price, Beginning balance	$ 3.16
Weighted-Average Exercise Price, Granted	4.61
Weighted-Average Exercise Price, Exercised	1.40
Weighted-Average Exercise Price, Cancelled or forfeited	4.30
Weighted-Average Exercise Price, Ending balance	3.26	$ 3.16
Weighted-Average Exercise Price, Vested and exercisable	$ 2.31
Weighted-Average Remaining Contractual Term Outstanding	5 years 10 months 13 days	6 years 4 months 2 days
Weighted-Average Remaining Contractual Term Outstanding, Vested and exercisable	4 years 4 months 20 days
Aggregate Intrinsic Value Outstanding	$ 528,000	$ 2,926,000
Aggregate Intrinsic Value, Vested and exercisable	$ 528,000
Predecessor Company [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Beginning balance	130,000	539,000	483,000	339,000
Number of Options, Granted		172,000	94,000	173,000
Number of Options, Exercised			(22,000)	(7,000)
Number of Options, Cancelled or forfeited		(581,000)	(16,000)	(22,000)
Number of Options, Ending balance		130,000	539,000	483,000
Number of Options, Exercisable		113,000
Weighted-Average Exercise Price, Beginning balance	$ 38.21	$ 52	$ 50.50	$ 51
Weighted-Average Exercise Price, Granted		18.40	50.80	49.10
Weighted-Average Exercise Price, Exercised			17.10	13.20
Weighted-Average Exercise Price, Forfeited/cancelled/expired		45.10	48.30	60.90
Weighted-Average Exercise Price, Ending balance		38.21	$ 52	$ 50.50
Weighted-Average Exercise Price, Vested, Exercisable		$ 42.91
Weighted-Average Remaining Contractual Term Outstanding		5 years 2 months 12 days
Weighted-Average Remaining Contractual Term Exercisable		4 years 6 months
Aggregate Intrinsic Value Outstanding		$ 16,000

Stockholders' Equity_Deficit _4

Stockholders' Equity/Deficit - Summary of Valuation of Stock Option Awards (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility		70.00%	76.30%	70.00%	59.00%
Risk-free interest rate		1.59%	0.45%	2.54%	2.60%
Expected term (in years)	0 years	6 years 3 months	6 years 3 months	6 years 3 months	1 year
Expected dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%

Stockholders' Equity_Deficit _5

Stockholders' Equity/Deficit - Summary of Compensation Cost Included in Condensed Consolidated Statements of Operations for Stock-based Compensation Arrangements (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	$ 125	$ 115	$ 456	$ 329	$ 438	$ 326
Cost of Product Revenue [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	(3)	9	16	26	38	25
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	2	9	8	31	$ 34	$ 54
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	$ 126	$ 97	$ 432	$ 272

Stockholders' Equity_Deficit _6

Stockholders' Equity/Deficit - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock warrants	4,929
Common stock options issued and outstanding		9,497,923
Total	2,229,933	48,099,217
Common stock available for issuance under the 2020 Plan	725,881
Common Stock [Member]
Class Of Stock [Line Items]
Common stock warrants	1,346
Common stock options issued and outstanding	1,499,123
Predecessor Company [Member]
Class Of Stock [Line Items]
Common stock warrants		1,000	1,000
Common stock options issued and outstanding		130,000	539,000
Common stock authorized for future option grants		395,000	84,000
RSUs outstanding		145,000
Common stock authorized for the ESPP		49,000	50,000
Total		720,000	674,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Jan. 31, 2020	May 31, 2015	Sep. 30, 2020	Dec. 31, 2019	Mar. 01, 2020	Jan. 01, 2020	Jan. 01, 2019	Jul. 31, 2010
Operating Leased Assets [Line Items]
Lease commencement date			Mar. 1, 2020
Lease expiration date	Aug. 31, 2031		Aug. 31, 2031
Right-of-use asset			$ 4,334,000	$ 95,000	$ 4,500,000	$ 619,000
Operating lease liability			$ 4,749,000	$ 108,000	$ 4,500,000	$ 707,000
Rent abatement term			6 months
Operating lease remaining term			11 years
Finance lease remaining term			3 years 8 months 12 days
Incremental borrowing rate			12.20%	12.00%
Finance lease weighted-average discount rate			10.00%	10.00%
Rent expense	$ 59,775
Conatus Pharmaceuticals Inc [Member]
Operating Leased Assets [Line Items]
Right-of-use asset			$ 100,000
Operating lease liability			$ 200,000
Office Space [Member]
Operating Leased Assets [Line Items]
Lease expiration date			Sep. 30, 2020
Predecessor Company [Member]
Operating Leased Assets [Line Items]
Right-of-use asset				$ 221,000			$ 600,000
Operating lease liability				$ 338,000			$ 700,000
Incremental borrowing rate				12.00%
ROU asset, impairment loss				$ 50,000
Amount payable upon the achievement of specified regulatory milestone								$ 18,000,000
Predecessor Company [Member] | Lease Agreements [Member]
Operating Leased Assets [Line Items]
Lease renewal term				5 years
Predecessor Company [Member] | Lease Agreements Two [Member]
Operating Leased Assets [Line Items]
Percentage of base rent escalator		3.00%
Rent expense		$ 33,000
Lease agreement rent expense for future period		$ 39,000
ROU asset, impairment loss				$ 50,000
Maximum [Member]
Operating Leased Assets [Line Items]
Tenant improvement allowance on modified lease			$ 2,200,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments of Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 01, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating lease
2020 (remaining 3 months)	$ 60
2021	616			$ 108
2022	757			0
2023	780			0
2024	803			0
Thereafter	6,010
Total minimum lease payments	9,026			108
Less: imputed interest	(4,277)			0
Total future minimum lease payments	4,749	$ 4,500	$ 707	108
Less: current obligations under leases	0			(108)
Noncurrent lease obligations	4,749			0
Finance lease
2020 (remaining 3 months)	3
2021	10			10
2022	10			10
2023	10			10
2024	5			10
Thereafter	0
Total minimum lease payments	38			46
Less: imputed interest	(5)			(9)
Total future minimum lease payments	33			37
Less: current obligations under leases	(8)			(6)	$ (25)
Noncurrent lease obligations	$ 25			$ 31	$ 7

Related Parties - Additional In

Related Parties - Additional Information (Detail)

Apr. 30, 2018USD ($)shares

Nov. 03, 2016USD ($)

Oct. 31, 2016USD ($)

Aug. 10, 2016

Apr. 21, 2016USD ($)

Mar. 20, 2016USD ($)

Feb. 15, 2016USD ($)

May 02, 2015USD ($)

Dec. 13, 2012USD ($)

Nov. 19, 2012

Apr. 30, 2020USD ($)Shareholder

Oct. 31, 2019USD ($)

Jan. 31, 2019shares

Mar. 31, 2018USD ($)

Jan. 31, 2016USD ($)shares

Nov. 30, 2012

Sep. 30, 2020USD ($)shares

Sep. 30, 2019USD ($)shares

Sep. 30, 2020USD ($)shares

Sep. 30, 2019USD ($)shares

Dec. 31, 2019USD ($)shares

Dec. 31, 2018USD ($)

Dec. 31, 2015USD ($)

Related Party Transaction [Line Items]

Number of promissory notes

2

Payment of outstanding principal and accrued interest

$ 7,000

$ 449,000

Convertible preferred stock issued | shares

0

0

0

Promissory Note [Member]

Related Party Transaction [Line Items]

Debt instrument, face amount

$ 300,000

Number of stockholders | Shareholder

2

Debt instrument interest amount

$ 25,000

Debt instrument, maturity date

Jun. 13, 2020

Number of days post merger that amounts are due

15 days

Common Stock [Member]

Related Party Transaction [Line Items]

Stock issued during period, shares | shares

675,480

16,158

675,480

21,885

152,594

Lordship Ventures Histogen Holdings LLC [Member]

Related Party Transaction [Line Items]

Percentage of outstanding voting shares controlled

19.00%

28.00%

29.00%

Interest expense

$ 23,000

Past due compensation

$ (50,000)

$ (25,000)

$ (25,000)

Debt instrument, related party interest rate

10.00%

10.00%

10.00%

Lordship Ventures Histogen Holdings LLC [Member] | Series B Convertible Preferred Stock [Member]

Related Party Transaction [Line Items]

Debt instrument, maturity date

Feb. 1, 2018

Shares, Issued | shares

114,445

Past due compensation

$ (2,600,000)

Debt instrument, related party interest rate

10.00%

Lordship Ventures Histogen Holdings LLC [Member] | Lordship Indemnification [Member] | Private Histogen [Member]

Related Party Transaction [Line Items]

Cash payment upon meeting additional capitalization threshold

$ 300,000

Additional accumulated capital for payment to be made

$ 10,000,000

Lordship Ventures Histogen Holdings LLC [Member] | Lordship Indemnification [Member] | Series B Convertible Preferred Stock [Member] | Private Histogen [Member]

Related Party Transaction [Line Items]

Warrants to purchase shares | shares

64,539

Stock issued during period, shares | shares

16,413

Lordship Ventures Histogen Holdings LLC [Member] | Success Fee Agreement [Member]

Related Party Transaction [Line Items]

Minimum percentage of asset or equity engaged in merger or sale transaction

90.00%

Related party expense recognized

$ 4,000

$ 2,000

$ 100,000

$ 800,000

$ 923,000

41,000

Lordship Ventures Histogen Holdings LLC [Member] | Success Fee Agreement [Member] | Private Histogen [Member]

Related Party Transaction [Line Items]

Minimum percentage of asset or equity engaged in merger or sale transaction

90.00%

Description of related party transaction

In November 2012, Private Histogen entered into a Strategic Relationship Success Fee Agreement with Lordship (the “Success Fee Agreement”). The Success Fee Agreement causes certain payments to be made from the Company to Lordship equal to 1% of certain product revenues and 10% of certain license and royalty revenues. The Success Fee Agreement also stipulates that if the Company engages in a merger or sale of all or substantially all (defined as 90% or more) of its assets or equity to a third party, then the Company has the option to terminate the agreement by paying Lordship the fair market value of future payments with the minimum payment being at least equal to the most recent annual payments Lordship has received.

In November 2012, Private Histogen entered into a Strategic Relationship Success Fee Agreement with Lordship (the “Success Fee Agreement”). The Success Fee Agreement causes certain payments to be made from the Company to Lordship equal to 1% of certain product revenues and 10% of certain license and royalty revenues. The Success Fee Agreement also stipulates that if the Company engages in a merger or sale of all or substantially all (defined as 90% or more) of its assets or equity to a third party, then the Company has the option to terminate the agreement by paying Lordship the fair market value of future payments with the minimum payment being at least equal to the most recent annual payments Lordship has received.

Lordship Ventures Histogen Holdings LLC [Member] | Allergan License Transfer Agreements [Member]

Related Party Transaction [Line Items]

Amount due to related parties

14,000

$ 14,000

$ 16,000

170,000

Lordship Ventures Histogen Holdings LLC [Member] | License And Royalty Revenue [Member] | Success Fee Agreement [Member] | Private Histogen [Member]

Related Party Transaction [Line Items]

Success fee percentage to be paid on certain product revenues

1.00%

Success fee percentage to be paid on certain license and royalty revenues

10.00%

Lordship Ventures Histogen Holdings LLC [Member] | Production Revenue [Member] | Success Fee Agreement [Member] | Private Histogen [Member]

Related Party Transaction [Line Items]

Success fee percentage to be paid on certain product revenues

1.00%

Success fee percentage to be paid on certain license and royalty revenues

10.00%

Lordship Ventures Histogen Holdings LLC [Member] | Common Stock [Member]

Related Party Transaction [Line Items]

Shares, Issued | shares

152,594

Lordship Ventures Histogen Holdings LLC [Member] | Common Stock [Member] | Lordship Indemnification [Member] | Private Histogen [Member]

Related Party Transaction [Line Items]

Stock issued during period, shares | shares

21,885

Stephen Chang [Member]

Related Party Transaction [Line Items]

Bonus for the deferment of payment

91,000

132,000

Accrued payables for consulting compensation

0

100,000

Stephen Chang [Member] | General and Administrative [Member]

Related Party Transaction [Line Items]

Consulting service expenses

$ 0

$ 100,000

$ 15,000,000,000

$ 100,000

Dr. Naughton [Member]

Related Party Transaction [Line Items]

Bonus for the deferment of payment

$ 23,000

$ 98,000

68,000

Deferred Compensation Agreement payment

$ 88,000

Payment due date

Jul. 25, 2018

Additional Compensation

$ 10,000

Dr. Naughton [Member] | Bridge Loan [Member]

Related Party Transaction [Line Items]

Advances from related party

$ 7,000

Debt instrument, related party interest rate

1000.00%

Payment of outstanding principal and accrued interest

$ 9,000

Dr. Naughton [Member] | Unpaid Amount [Member]

Related Party Transaction [Line Items]

Consulting service expenses

0

$ 68,000

Dr. Naughton [Member] | Promissory Notes [Member]

Related Party Transaction [Line Items]

Past due compensation

229,000

Eileen Brandt [Member]

Related Party Transaction [Line Items]

Bonus for the deferment of payment

18,000

Promissory note issued to related party

23,000

Amount of bonus for deferment of payment to employee

$ 3,000

Dr. David Crean [Member]

Related Party Transaction [Line Items]

Bonus for the deferment of payment

20,000

93,000

Accrued payables to related party

0

20,000

Clinica [Member]

Related Party Transaction [Line Items]

Licensing deposit liability

$ 150,000

Amount of expensed fair value of convertible preferred stock issued excluded licensing deposit liability

363,000

Clinica [Member] | Convertible Preferred Stock Series D [Member]

Related Party Transaction [Line Items]

Convertible preferred stock issued | shares

341,667

Anti-Cancer Inc.[Member]

Related Party Transaction [Line Items]

Outstanding amounts owed to related party

$ 22,000

$ 22,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($)	Jan. 31, 2020	Jan. 28, 2020	Jan. 17, 2020	Nov. 30, 2020	May 31, 2017	Sep. 30, 2020	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Subsequent Event [Line Items]
Warrants to purchase common stock						4,929
Proceeds from offering						$ 1,337,000
Reimburse the other party's expenses			$ 1,000,000
Lease expiration date	Aug. 31, 2031					Aug. 31, 2031
Lease base rent	$ 59,775
Merger Agreement [Member]
Subsequent Event [Line Items]
Termination fee		$ 500,000
Maximum [Member] | Merger Agreement [Member]
Subsequent Event [Line Items]
Reimburse the other party's expenses		350,000
Predecessor Company [Member]
Subsequent Event [Line Items]
Warrants to purchase common stock								1,000	1,000
Proceeds from offering					$ 30,600,000		$ 30,610,000
Predecessor Company [Member] | Subsequent Event [Member] | Merger Agreement [Member]
Subsequent Event [Line Items]
Termination fee		500,000
Predecessor Company [Member] | Maximum [Member] | Subsequent Event [Member] | Merger Agreement [Member]
Subsequent Event [Line Items]
Reimburse the other party's expenses		$ 350,000
Common Stock [Member]
Subsequent Event [Line Items]
Warrants to purchase common stock						1,346
Common Stock [Member] | Maximum [Member]
Subsequent Event [Line Items]
Warrants to purchase common stock										3,583
Registered Direct Offering [Member] | Common Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of common stock shares sold				2,522,784
Sale of common stock price per share				$ 1.78375
Warrants to purchase common stock				1,892,088
Proceeds from offering				$ 4,500,000

Organization and Nature of Oper

Organization and Nature of Operations - Additional Information (Detail) - USD ($)	Jan. 28, 2020	Jan. 17, 2020
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Reimburse the other party's expenses		$ 1,000,000
Merger Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Termination fee	$ 500,000
Merger Agreement [Member] | Maximum [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Reimburse the other party's expenses	$ 350,000

Liquidity and Going Concern - A

Liquidity and Going Concern - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated losses	$ (59,194)	$ (43,933)
Cash and cash equivalents	$ 6,649	$ 2,065	$ 3,758	$ 3,027

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail)	Jan. 12, 2018USD ($)$ / sharesshares	Dec. 31, 2016Performance_Obligation	Sep. 30, 2020USD ($)	Sep. 30, 2019	Sep. 30, 2020USD ($)Segment	Sep. 30, 2019	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)	Mar. 01, 2020USD ($)	Jan. 01, 2020USD ($)	Jan. 01, 2019USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of AB common shares purchased | shares								100,000
Maximum entity ownership percentage required for variable interest entity					100.00%		100.00%
Number of operating segment | Segment					1		1
Allowance for doubtful accounts							$ 0	$ 22,000
Impairment losses recognized					$ 0		0
ROU assets			$ 4,334,000		4,334,000		95,000			$ 4,500,000	$ 619,000
Lease liabilities			4,749,000		4,749,000		108,000			$ 4,500,000	$ 707,000
One Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer			$ 100,000		$ 100,000		100,000
Revenues							$ 10,500,000	$ 860,000
Revenue Benchmark [Member] | Customer Concentration Risk [Member] | One Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of revenues			100.00%	39.00%	100.00%	94.00%	91.00%	48.00%
Previously Reported [Member]
Summary Of Significant Accounting Policies [Line Items]
ROU assets							$ 95,000
Previously Reported [Member] | One Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer							$ 11,000	$ 21,000
Variable Interest Entity ("VIE")
Summary Of Significant Accounting Policies [Line Items]
Variable interest entity percentage	68.00%						50.00%
Variable interest entity common stock shares owned | $ / shares	$ 2,600,000
Variable Interest Entity ("VIE") | Plan of Conversion Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of common shares specified in Plan of Conversion | shares	3,800,000
Number of AB common shares purchased | shares	100,000
Price per Share Purchase Price of AB common shares	$ 1
Aggregate Purchase Price of AB common shares | $ / shares	$ 100,000
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets					5 years		5 years
Predecessor Company [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of operating segment | Segment							1
Impairment losses recognized							$ 50,000
Realized gains and losses on investments							0	0	$ 0
Other-than-temporary declines in value of marketable securities							$ 0	0	0
Collaboration and license agreement termination period							Sep. 30, 2019
Unrecognized tax benefits that would, if recognized, affect the Company's effective tax rate							$ 0
Recognized interest or penalties on income tax							$ 0	$ 0	$ 0
Risk-free interest rate basis							The risk-free interest rate is based on the average yield of five-and seven-year U.S. Treasury Bills as of the valuation date.
ROU assets							$ 221,000					$ 600,000
Lease liabilities							338,000					$ 700,000
Predecessor Company [Member] | Collaborative Arrangement [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized royalty revenue							$ 0
Predecessor Company [Member] | Collaborative Arrangement [Member] | Novartis [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of significant performance obligations | Performance_Obligation		2
Collaboration and license agreement termination period							Sep. 30, 2019
Predecessor Company [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets							3 years
Predecessor Company [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets							5 years

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Summary of Assets and Liabilities Measured at Fair Value (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value	$ 515
Indemnification liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value	239
Warrants Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value	276
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value	515
Level 3 [Member] | Indemnification liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value	239
Level 3 [Member] | Warrants Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities fair value	$ 276

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Liabilities Measured at Fair Value Using Level 3 (Detail) - Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Indemnification liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 239
Issuance		$ 182
Change in fair value		57
Settlement	(239)
Ending balance		239
Warrants Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	276	229
Change in fair value	$ (276)	47
Ending balance		$ 276

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Black-Scholes Option Pricing Model Assumptions (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility		70.00%	76.30%	70.00%		59.00%
Risk-free interest rate		1.59%	0.45%	2.54%		2.60%
Expected term (in years)	0 years	6 years 3 months	6 years 3 months	6 years 3 months		1 year
Expected dividend yield	0.00%	0.00%	0.00%	0.00%		0.00%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)			10 years
Predecessor Company [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate - Minimum					1.82%	2.55%	1.83%
Risk-free interest rate - Maximum					2.50%	3.03%	2.13%
Expected dividend yield					0.00%	0.00%	0.00%
Expected volatility - Minimum					105.00%	94.00%	93.00%
Expected volatility - Maximum					119.00%	100.00%	97.00%
Predecessor Company [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)					5 years 6 months	5 years 6 months	5 years 6 months
Predecessor Company [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)					6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	1,504,052	6,515,951	44,707,805	40,686,102
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	4,929	3,585	25,000	25,000
Common stock options issued and outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities			9,497,923	6,150,000
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		5,046,213	35,184,882	33,561,102
Warrants to Purchase Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		107,565		950,000
Predecessor Company [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities			276,000	540,000	793,000
Predecessor Company [Member] | Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities			1,000	1,000	15,000
Predecessor Company [Member] | Common stock options issued and outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities			130,000	539,000	482,000
Predecessor Company [Member] | Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities			145,000
Predecessor Company [Member] | Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities					296,000

Notes Payable - Related Party -

Notes Payable - Related Party - Additional Information (Detail) $ / shares in Units, $ in Thousands	Feb. 01, 2018USD ($)	Oct. 31, 2016	Aug. 10, 2016Note	Apr. 21, 2016USD ($)shares	Mar. 20, 2016USD ($)shares	Feb. 15, 2016USD ($)shares	Jan. 14, 2016USD ($)	Dec. 13, 2012USD ($)$ / shares	Dec. 31, 2018USD ($)$ / shares
Lordship Ventures Histogen Holdings LLC [Member]
Related Party Transaction [Line Items]
Notes payable, related party				$ 50	$ 25	$ 25
Debt instrument, related party interest rate				10.00%	10.00%	10.00%
Minimum equity capital to be raised									$ 3,000
Strike price per share | $ / shares									$ 1.5
Warrants expiration									Dec. 31, 2018
Lordship Ventures Histogen Holdings LLC [Member] | Conversion Termination and Release Agreement [Member]
Related Party Transaction [Line Items]
Number of outstanding remaining notes extended | Note			2
Debt instrument, maturity date			Jul. 25, 2018
Debt instrument, early extinguishment date			Aug. 10, 2016
Lordship Ventures Histogen Holdings LLC [Member] | Conversion Termination and Release Agreement [Member] | Minimum [Member]
Related Party Transaction [Line Items]
Percentage of change in present value of cash flow			10.00%
Lordship Ventures Histogen Holdings LLC [Member] | Warrants Issued February 15 [Member]
Related Party Transaction [Line Items]
Fair value of warrants									$ 4
Lordship Ventures Histogen Holdings LLC [Member] | Warrants Issued March 20 [Member]
Related Party Transaction [Line Items]
Fair value of warrants									5
Lordship Ventures Histogen Holdings LLC [Member] | Warrants Issued April 21 [Member]
Related Party Transaction [Line Items]
Fair value of warrants									$ 10
Lordship Ventures Histogen Holdings LLC [Member] | Convertible Preferred Stock Series D [Member]
Related Party Transaction [Line Items]
Warrant to purchase shares | shares				100,000	50,000	50,000
Lordship Ventures Histogen Holdings LLC [Member] | Series B Convertible Preferred Stock [Member]
Related Party Transaction [Line Items]
Notes payable, related party								$ 2,600
Debt instrument, related party interest rate								10.00%
Debt instrument, maturity date			Feb. 1, 2018
Preferred stock, per share | $ / shares								$ 1
Lordship Ventures Histogen Holdings LLC [Member] | Series B Convertible Preferred Stock [Member] | Minimum [Member]
Related Party Transaction [Line Items]
Convertible notes payable								$ 11
Lordship Ventures Histogen Holdings LLC [Member] | Series B Convertible Preferred Stock [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Convertible notes payable								$ 400
Lordship Ventures Histogen Holdings LLC [Member] | Series B Convertible Preferred Stock [Member] | Conversion Termination and Release Agreement [Member]
Related Party Transaction [Line Items]
Payments of convertible preferred stock	$ 375
Accumulated accrued interest forgiven upon conversion	$ 1,400
Dr. Naughton [Member] | Bridge Loan [Member]
Related Party Transaction [Line Items]
Notes payable, related party							$ 7
Debt instrument, related party interest rate							10.00%
Certain employees, including Dr. Naughton
Related Party Transaction [Line Items]
Debt instrument, related party interest rate		5.00%
Debt instrument, maturity date		Dec. 31, 2018

Lease - Additional Information

Lease - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2020USD ($)	Mar. 01, 2020USD ($)	Jan. 01, 2020USD ($)
Commitments and Contingencies Disclosure [Abstract]
Weighted-average remaining lease term, operating lease	2 months 12 days
Weighted-average remaining lease term, finance lease	4 years 6 months
Lease right-of-use asset	$ 95	$ 4,334	$ 4,500	$ 619
Lease liability	$ 108	$ 4,749	$ 4,500	$ 707
Weighted average discount rate, operating leases	12.00%	12.20%
Weighted average discount rate, finance leases	10.00%	10.00%
Number of renewal terms	1
Renewal term	5 years

Leases - Summary of Lease Asset

Leases - Summary of Lease Assets and Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 01, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease	$ 4,334	$ 4,500	$ 619	$ 95
Finance leases				37
Total lease assets				132
Operating lease liability	0			108
Finance lease liabilities	8			6	$ 25
Total current liabilities				114
Operating lease liability	4,749			0
Finance lease liabilities	$ 25			31	$ 7
Total noncurrent liabilities				31
Total lease liabilities				$ 145

Leases - Summary of Components

Leases - Summary of Components of Lease Expense (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Leases [Line Items]
Total operating lease cost	$ 570
Amortization of right-of-use assets Property and equipment, net	25
Interest on lease liabilities Interest expense	5
Total finance lease cost	30
Cost of Product Revenue [Member]
Leases [Line Items]
Total operating lease cost	165
Research and Development [Member]
Leases [Line Items]
Total operating lease cost	245
General and Administrative [Member]
Leases [Line Items]
Total operating lease cost	$ 160

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Payments of Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 01, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating lease
2020	$ 616			$ 108
2021	757			0
2022	780			0
2023	803			0
2024				0
Total minimum lease payments	9,026			108
Less: imputed interest	(4,277)			0
Total future minimum lease payments	4,749	$ 4,500	$ 707	108
Less: current obligations under leases	0			(108)
Noncurrent lease obligations	4,749			0
Finance lease
2020	10			10
2021	10			10
2022	10			10
2023	5			10
2024				6
Total minimum lease payments	38			46
Less: imputed interest	(5)			(9)
Total future minimum lease payments	33			37
Less: current obligations under leases	(8)			(6)	$ (25)
Noncurrent lease obligations	$ 25			$ 31	$ 7

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Related to Leases (Detail) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating lease			$ 570
Operating cash flows from finance leases			5
Financing cash flows from finance leases			25
Right-of-use asset obtained in exchange for operating lease liability	$ 4,481	$ 619	619
Right-of-use asset obtained in exchange for new finance lease liability		$ 40	$ 40

Forward Purchase Contract - Add

Forward Purchase Contract - Additional Information (Detail) - USD ($)	Jan. 26, 2017	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Long-term Purchase Commitment [Line Items]
EPS unpaid services		$ 300,000	$ 340,000
Shares issued		0	0
Fair value of liability		$ 300,000	$ 290,000	$ 290,000
Settlement Agreement [Member]
Long-term Purchase Commitment [Line Items]
Cash paid	$ 50,000
Share repurchases, description		The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $0.3 million at September 30, 2020 and December 31, 2019, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. The Company has the sole option to initiate the timing of the repurchase of the shares (which were converted into shares of common stock upon the Merger) before the deadline date.	The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $290 thousand, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. Histogen has the sole option to initiate the timing of the repurchase of the shares before the deadline date.
Share repurchases, value		$ 300,000	$ 290,000
Gain (Loss) on extinguishment of the original liability	$ 0
Settlement Agreement [Member] | Series D Convertible Preferred Stock [Member]
Long-term Purchase Commitment [Line Items]
Shares issued	14,342
Settlement Agreement [Member] | Series D Convertible Preferred Stock [Member] | Previously Reported [Member]
Long-term Purchase Commitment [Line Items]
Shares issued	100,000

Convertible Preferred Stock - S

Convertible Preferred Stock - Schedule of Outstanding Convertible Preferred Stock (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Temporary Equity [Line Items]
Shares Authorized	0	73,000,000
Shares Issued and Outstanding		5,046,154
Liquidation Preference	$ 0	$ 40,294
Carrying Value	$ 0	$ 39,070	$ 39,070	$ 39,070	$ 36,683
Convertible Preferred Stock Series A [Member]
Temporary Equity [Line Items]
Shares Authorized		10,000,000
Shares Issued and Outstanding		1,360,547
Liquidation Preference		$ 9,486
Convertible Preferred Stock Series B [Member]
Temporary Equity [Line Items]
Shares Authorized		35,000,000
Shares Issued and Outstanding		1,144,567
Liquidation Preference		$ 7,981
Convertible Preferred Stock Series C [Member]
Temporary Equity [Line Items]
Shares Authorized		8,000,000
Shares Issued and Outstanding		1,075,637
Liquidation Preference		$ 7,500
Convertible Preferred Stock Series D [Member]
Temporary Equity [Line Items]
Shares Authorized		20,000,000
Shares Issued and Outstanding		1,465,403
Liquidation Preference		$ 15,327
Previously Reported [Member]
Temporary Equity [Line Items]
Shares Authorized		73,000,000			73,000,000
Shares Issued and Outstanding		35,184,882			33,561,102
Liquidation Preference		$ 40,294			$ 37,915
Carrying Value		$ 39,070			$ 36,683	$ 30,064
Previously Reported [Member] | Convertible Preferred Stock Series A [Member]
Temporary Equity [Line Items]
Shares Authorized		10,000,000			10,000,000
Shares Issued and Outstanding		9,486,575			9,486,575
Liquidation Preference		$ 9,486			$ 9,486
Carrying Value		$ 9,486			$ 9,486
Previously Reported [Member] | Convertible Preferred Stock Series B [Member]
Temporary Equity [Line Items]
Shares Authorized		35,000,000			35,000,000
Shares Issued and Outstanding		7,980,620			7,866,175
Liquidation Preference		$ 7,981			$ 7,866
Carrying Value		$ 9,356			$ 9,232
Previously Reported [Member] | Convertible Preferred Stock Series C [Member]
Temporary Equity [Line Items]
Shares Authorized		8,000,000			8,000,000
Shares Issued and Outstanding		7,500,000			7,500,000
Liquidation Preference		$ 7,500			$ 7,500
Carrying Value		$ 5,550			$ 5,550
Previously Reported [Member] | Convertible Preferred Stock Series D [Member]
Temporary Equity [Line Items]
Shares Authorized		20,000,000			20,000,000
Shares Issued and Outstanding		10,217,687			8,708,352
Liquidation Preference		$ 15,327			$ 13,063
Carrying Value		$ 14,678			$ 12,415

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jan. 12, 2016	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Temporary Equity [Line Items]
Warrants to purchase stock					4,929
Convertible Preferred Stock Conversion Feature | Minimum [Member]
Temporary Equity [Line Items]
Proceeds from issuance of convertible preferred stock			$ 20,000
Sale of stock price per share			$ 4.50
Indemnification liability [Member]
Temporary Equity [Line Items]
One-time cash payment	$ 300
Indemnification liability [Member] | After May 1, 2015 [Member]
Temporary Equity [Line Items]
Additional accumulated capital investment	$ 10,000
Convertible Preferred Stock Series B [Member]
Temporary Equity [Line Items]
Convertible preferred stock issued		16,413	2,592,000	114,445
Stock issued price per share			$ 1	$ 1
Temporary equity liquidation preference per share		$ 6.97
Convertible Preferred Stock Series B [Member] | Previously Reported [Member]
Temporary Equity [Line Items]
Convertible preferred stock issued			114,445	2,592,000
Convertible Preferred Stock Series B [Member] | Indemnification liability [Member]
Temporary Equity [Line Items]
Warrants to purchase stock	450,000
Convertible Preferred Stock Series D [Member]
Temporary Equity [Line Items]
Convertible preferred stock issued		49,144	1,509,335	1,742,167
Stock issued price per share			$ 1.50	$ 1.50
Temporary equity liquidation preference per share		$ 10.46	$ 1.50		$ 10.46
Convertible Preferred Stock Series D [Member] | Previously Reported [Member]
Temporary Equity [Line Items]
Convertible preferred stock issued			342,668	1,400,500
Convertible Preferred Stock Series D [Member] | PUR Biologics, LLC [Member] | Development Assets | Previously Reported [Member]
Temporary Equity [Line Items]
Convertible preferred stock issued			1,166,667
Noncumulative Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock dividend rate percentage			6.00%
Convertible Preferred Stock Series A, B and C [Member]
Temporary Equity [Line Items]
Temporary equity liquidation preference per share			$ 1		$ 6.97

Warrants - Additional Informati

Warrants - Additional Information (Detail) - $ / shares	Oct. 20, 2016	Jan. 01, 2016	Feb. 26, 2010	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Class of Warrant or Right [Line Items]
Warrants outstanding				4,929
Common Stock [Member]
Class of Warrant or Right [Line Items]
Exercise price of warrants				$ 74.30			$ 23.08
Warrant expiration date				Jul. 3, 2023			Jul. 31, 2021
Warrants outstanding				1,346
Exchange for rent on a premise lease | Convertible Preferred Stock Series A [Member]
Class of Warrant or Right [Line Items]
Warrants issued during the period			300,000
Exercise price of warrants			$ 1
Warrant expiration date			Dec. 31, 2019
Advisory Services [Member] | Convertible Preferred Stock Series B [Member]
Class of Warrant or Right [Line Items]
Warrants issued during the period	450,000
Exercise price of warrants	$ 1
Warrant expiration date	Dec. 31, 2019
Gar Wood Securities, LLC | Common Stock [Member]
Class of Warrant or Right [Line Items]
Warrants issued during the period		25,000
Exercise price of warrants		$ 3.31
Warrant expiration date		Jul. 31, 2021
Warrants outstanding					0	0

Stock Based Compensation Expens

Stock Based Compensation Expenses - Additional Information (Detail)	Jan. 28, 2020USD ($)	Jan. 24, 2019shares	Apr. 30, 2019shares	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Nov. 28, 2007shares
Share Based Compensation [Line Items]
Unrecognized compensation expense | $					$ 1,100,000	$ 373,000
Unrecognized compensation expense, expected vesting period					0	0
Stock options exercised | $				$ 40,000		$ 77,000
Stock Options [Member]
Share Based Compensation [Line Items]
performance-based stock options exercisable					0
Stock options expenses | $					$ 0
Stock Options [Member]
Share Based Compensation [Line Items]
Stock options exercised pursuant to cashless exercise					250,000	225,000
Forfeited shares to cover aggregate exercise price					45,231	63,637
Issuance of common stock upon net exercise of stock options, shares					204,769	161,363
Stock options exercised | $					$ 129,000
Liquidity Option Shares [Member]
Share Based Compensation [Line Items]
Number of shares granted	12 months
Vesting percentage	25.00%
Vesting term				The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $200.0 million; (3) the date that the market capitalization of the Company exceeds $275.0 million, and; (4) the date that the market capitalization of the Company exceeds $300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination.	The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $200.0 million; (3) the date that the market capitalization of the Company exceeds $275.0 million, and; (4) the date that the market capitalization of the Company exceeds $300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination.
Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche One [Member]
Share Based Compensation [Line Items]
Vesting percentage	40.00%
Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche Two [Member]
Share Based Compensation [Line Items]
Minimum market capitalization amount required for vesting | $	$ 200,000,000
Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche Three [Member]
Share Based Compensation [Line Items]
Minimum market capitalization amount required for vesting | $	275,000,000
Liquidity Option Shares [Member] | Sharebased Compensation Award Tranche Four [Member]
Share Based Compensation [Line Items]
Minimum market capitalization amount required for vesting | $	$ 300,000,000
Chief Executive Officer [Member] | Performance Shares [Member]
Share Based Compensation [Line Items]
Number of shares granted		36 months
Number of shares issued under share-based payment arrangement		3,382,923
Chief Executive Officer [Member] | Performance Shares [Member] | Share-based Payment Arrangement, Tranche One [Member]
Share Based Compensation [Line Items]
Vesting percentage		40.00%
Remaining vesting percentage		25.00%
Chief Executive Officer [Member] | Performance Shares [Member] | Share-based Payment Arrangement, Tranche Two [Member]
Share Based Compensation [Line Items]
Vesting percentage		60.00%
Chief Executive Officer [Member] | Stock Options [Member]
Share Based Compensation [Line Items]
Number of shares granted		36 months
Number of shares issued under share-based payment arrangement		485,178
Vesting term				In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months.	In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months.
Chief Executive Officer [Member] | Stock Options [Member] | Share-based Payment Arrangement, Tranche One [Member]
Share Based Compensation [Line Items]
Vesting percentage		40.00%
Remaining vesting percentage		25.00%
Chief Executive Officer [Member] | Stock Options [Member] | Share-based Payment Arrangement, Tranche Two [Member]
Share Based Compensation [Line Items]
Vesting percentage		60.00%
Employee and Director [Member]
Share Based Compensation [Line Items]
Stock options, Granted					3,700,000	1,200,000
Weighted-average grant date fair value per share | $ / shares					$ 0.49	$ 0.35
Non Employees [Member]
Share Based Compensation [Line Items]
Stock options, Granted						200,000
Weighted-average grant date fair value per share | $ / shares						$ 0.34
Two Thousand Seven Equity Plan [Member]
Share Based Compensation [Line Items]
Number of share authorized							14,000,000
Number of shares granted					4 years
Share-based compensation arrangement by share-based payment award, expiration period					10 years
Share-based compensation arrangement by share-based payment award, expiration date					Nov. 30, 2017
Number of shares issued under share-based payment arrangement					0	0
Two Thousand Seventeen Equity Incentive Plan [Member]
Share Based Compensation [Line Items]
Number of share authorized							5,800,000
Share-based compensation arrangement by share-based payment award, number of additional shares authorized			2,278,007

Stock Based Compensation Expe_2

Stock Based Compensation Expenses - Summary related to stock option (Detail) - 2007 and 2017 Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation [Line Items]
Number of Options, Beginning balance	6,150,000	5,730,000
Number of Options, Granted	3,722,923	1,400,000
Number of Options, Exercised	(250,000)	(790,000)
Number of Options, Cancelled or forfeited	(125,000)	(190,000)
Number of Options, Ending balance	9,497,923	6,150,000	5,730,000
Weighted-Average Exercise Price, Beginning balance	$ 0.26	$ 0.17
Number of Options, Vested and exercisable	5,272,552
Weighted-Average Exercise Price, Granted	$ 0.76	0.57
Weighted-Average Exercise Price, Exercised	0.14	0.14
Weighted-Average Exercise Price, Cancelled or forfeited	0.63	0.42
Weighted-Average Exercise Price, Ending balance	0.45	$ 0.26	$ 0.17
Weighted-Average Exercise Price, Vested and exercisable	$ 0.23
Weighted-Average Remaining Contractual Term Outstanding	6 years 4 months 2 days	5 years 7 months 6 days	5 years 1 month 6 days
Weighted-Average Remaining Contractual Term Outstanding, Vested and exercisable	4 years 2 months 26 days
Aggregate Intrinsic Value Outstanding	$ 2,926	$ 3,098	$ 2,174
Aggregate Intrinsic Value, Vested and exercisable	$ 2,814

Stock Based Compensation Expe_3

Stock Based Compensation Expenses - Valuation of stock option award (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation [Line Items]
Expected volatility		70.00%	76.30%	70.00%		59.00%
Risk-free interest rate		1.59%	0.45%	2.54%		2.60%
Expected contractual term	0 years	6 years 3 months	6 years 3 months	6 years 3 months		1 year
Expected dividend yield	0.00%	0.00%	0.00%	0.00%		0.00%
Share-based Payment Arrangement [Member]
Share Based Compensation [Line Items]
Expected volatility					70.00%	63.90%
Risk-free interest rate					2.50%	2.80%
Expected contractual term					6 years 3 months	6 years 3 months
Expected dividend yield					0.00%	0.00%

Stock Based Compensation Expe_4

Stock Based Compensation Expenses - Summary of compensation cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation [Line Items]
Stock-based compensation expense	$ 125	$ 115	$ 456	$ 329	$ 438	$ 326
Cost of Product Revenue [Member]
Share Based Compensation [Line Items]
Stock-based compensation expense	(3)	9	16	26	38	25
Research and Development [Member]
Share Based Compensation [Line Items]
Stock-based compensation expense	$ 2	$ 9	$ 8	$ 31	34	54
Selling, General and Administrative Expenses [Member]
Share Based Compensation [Line Items]
Stock-based compensation expense					$ 366	$ 247

Stock Based Compensation Expe_5

Stock Based Compensation Expenses - Common Stock Reserved (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020
Share Based Compensation [Line Items]
Common stock warrants	25,000
Convertible preferred stock (if converted)	35,184,882
Common stock options issued and outstanding	9,497,923
Common stock reserved for future issuance	48,099,217	2,229,933
Two Thousand Seventeen Equity Incentive Plan [Member]
Share Based Compensation [Line Items]
Common stock available for issuance under the Plan	3,391,412

Non controlling Interest - Summ

Non controlling Interest - Summary of Changes in Company's Ownership (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Net loss attributable to Histogen, Inc. stockholders	$ (3,249)	$ (1,694)	$ (15,261)	$ (656)	$ (2,966)	$ (6,125)
Decrease in Histogen, Inc.'s paid-in capital for purchase of 100,000 common shares of AB from noncontrolling interest						(100)
Change from net loss attributable to Histogen, Inc. stockholders and transfers to noncontrolling interest					$ (2,966)	$ (6,225)

Non controlling Interest - Su_2

Non controlling Interest - Summary of Changes in Company's Ownership (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018shares
Noncontrolling Interest [Abstract]
Number of AB common shares purchased	100,000

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Postemployment Benefits [Abstract]
Minimum percentage of elgible compensation	1.00%
Maximum percentage of elgible compensation	100.00%
Percentage of contributions of employees salary deferrals up	25.00%
Maximum contribution amount per each employee	$ 2,500
Employee contributions	$ 0	$ 37,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Research credit carryforwards expiration year		2027
Cumulative change in ownership percentage		50.00%
Period for cumulative change in ownership percentage		3 years
Deferred tax asset, change in valuation allowance amount		$ 900,000	$ 1,700,000
Income tax rate	21.00%	21.00%	21.00%
Income tax rate effective date	Jan. 1, 2018
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Percentage of future taxable income		80.00%	80.00%
Federal and California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		$ 38,300,000
Operating loss carryforwards		$ 7,600,000	$ 7,600,000
Operating loss carryforwards expiration year		2018
Research credit carryforwards		$ 900,000
Predecessor Company [Member]
Operating Loss Carryforwards [Line Items]
Research credit carryforwards expiration year		2027
Cumulative change in ownership percentage		50.00%
Period for cumulative change in ownership percentage		3 years
Deferred tax asset, change in valuation allowance amount		$ 700,000	$ 4,400,000	$ (9,000,000)
Income tax rate		21.00%	21.00%	34.00%
Minimum percentage of likelihood for uncertain tax position to be recognized		50.00%
Recognized interest or penalties on income tax		$ 0	$ 0	$ 0
Predecessor Company [Member] | Federal and California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		$ 145,500,000
Operating loss carryforwards expiration year		2028
Research credit carryforwards		$ 8,300,000
California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		38,100,000
Research credit carryforwards		800,000
California [Member] | Predecessor Company [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		76,400,000
Research credit carryforwards		2,400,000
Federal and California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		$ 30,700,000	$ 30,500,000

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Taxes Based On Losses From Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Current
Federal	$ 0	$ 0
State	(1)	(1)
Total	(1)	(1)
Deferred
Federal	736	1,277
State	180	455
Total	916	1,732
Less valuation allowance	(916)	(1,732)
Income tax expense	$ (1)	$ (1)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Taxes Computed Using The Statutory U.S. Income Tax Rate and The Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Thousands	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate		$ (589)	$ (1,256)
State tax, net of federal tax benefits		(194)	(392)
Permanent items		5	104
Tax credits		(66)	(157)
Tax rate change		0	(18)
Valuation allowance increase		916	1,732
Other		(71)	(12)
Provision for income taxes		$ 1	$ 1
Tax computed at federal statutory rate	21.00%	21.00%	21.00%
State tax, net of federal tax benefits		6.92%	6.56%
Permanent items		(0.18%)	(1.74%)
Tax credits		2.35%	2.62%
Tax rate change		0.00%	0.31%
Valuation allowance increase		(32.65%)	(28.74%)
Other		2.53%	0.01%
Effective tax rate		(0.04%)	0.01%

Income Taxes - Components of Co

Income Taxes - Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Net operating loss carryovers	$ 10,757	$ 9,986
R&D credits and other tax credits	1,540	1,455
Compensation	60	71
Other	947	876
Total deferred tax assets	13,304	12,388
Deferred tax liabilities
Less valuation allowance	(13,304)	(12,388)
Deferred tax assets, net	0	0
Predecessor Company [Member]
Deferred tax assets
Net operating loss carryovers	35,901	31,135
R&D credits and other tax credits	8,312	8,641
Intangibles	130	379
Stock options	438	2,255
Compensation	47	452
Deferred revenue		2,642
Other	88	62
Total deferred tax assets	44,916	45,566
Deferred tax liabilities
Right-of-use asset	46
Total net deferred tax assets	44,870	45,566
Less valuation allowance	(44,870)	(45,566)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Balance at beginning of year	$ 0
Additions based on tax positions related to the current year	108
Additions from tax positions taken in prior years	366
Balance at end of year	474	$ 0
Predecessor Company [Member]
Operating Loss Carryforwards [Line Items]
Balance at beginning of year	2,221	1,932	$ 1,319
Additions based on tax positions related to the current year		289	613
Reductions based on tax positions related to prior years	(80)
Balance at end of year	$ 2,141	$ 2,221	$ 1,932

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (43,933)	$ (59,194)
Cash and cash equivalents	$ 2,065	$ 6,649	$ 3,758	$ 3,027
Predecessor Company [Member]
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation	Jul. 13, 2005
Accumulated deficit	$ (198,014)			(186,629)
Cash and cash equivalents	20,703			$ 11,565
Working capital	$ 20,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value (Detail) - Predecessor Company [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 20,703	$ 40,692
Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	1,870	2,072
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	18,833	8,000
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		30,620
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	20,703	10,072
Level 1 [Member] | Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	1,870	2,072
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 18,833	8,000
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		30,620
Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		$ 30,620

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Predecessor Company [Member]
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 0	$ 29,127,000

Marketable Securities - Summary

Marketable Securities - Summary of Investments in Marketable Securities (Detail) - Predecessor Company [Member] - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 29,144,000
Unrealized Gains		0
Unrealized Losses		(17,000)
Estimated Fair Value	$ 0	29,127,000
Corporate debt securities 1 or less years of maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		29,144,000
Unrealized Gains		0
Unrealized Losses		(17,000)
Estimated Fair Value		$ 29,127,000

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) - Predecessor Company [Member] - USD ($)	Dec. 05, 2018	Feb. 15, 2017	Jan. 24, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 19, 2016	Jul. 31, 2010
Debt and Financial Instruments [Line Items]
Conversion of convertible note payable						$ 13,729,000
Proceeds from issuance of convertible note payable							$ 12,500,000
Novartis [Member] | Investment Agreement [Member]
Debt and Financial Instruments [Line Items]
Debt instrument, interest rate				6.00%
Debt instrument, maturity date				Dec. 31, 2019
Deferred revenue								$ 2,500,000
Promissory note [Member] | Pfizer Inc. [Member]
Debt and Financial Instruments [Line Items]
Note payable									$ 1,000,000
Debt instrument, interest rate					7.00%
Debt instrument, maturity date					Jul. 29, 2020
Prepayment of notes payable			$ 1,004,861
Convertible Promissory Note [Member] | Novartis [Member]
Debt and Financial Instruments [Line Items]
Debt instrument, interest rate		6.00%
Debt instrument, maturity date		Dec. 31, 2019
Promissory note, principal amount		$ 15,000,000
Promissory note conversion, description					The terms of the Novartis Note allowed the Company to convert the principal and accrued interest into the Company's common stock at a conversion price equal to 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date.
Principal and accrued interest of note to be converted into common stock at conversion price, in percentage		120.00%
Trailing period for average closing price per share of common stock		20 days
Conversion of convertible note payable	$ 15,000,000
Proceeds from issuance of convertible note payable		$ 15,000,000
Convertible note payable		12,500,000
Reduction of outstanding receivable		2,500,000
Conversion of convertible note payable to common stock	288,251
Conversion price	$ 57.70
Fair value of convertible note payable					$ 12,500,000
Convertible Promissory Note [Member] | Novartis [Member] | Investment Agreement [Member]
Debt and Financial Instruments [Line Items]
Promissory note, principal amount		$ 15,000,000
Principal and accrued interest of note to be converted into common stock at conversion price, in percentage		120.00%
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	288,251
Conversion price	$ 57.70

Stockholders' Equity_Deficit _7

Stockholders' Equity/Deficit - Summary of RSU Activity (Detail) - Restricted Stock Units (RSUs) [Member] - Predecessor Company [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total RSUs, Beginning balance | shares	0
Total RSUs, Granted | shares	160
Total RSUs, Forfeited | shares	(15)
Total RSUs, Ending balance | shares	145
Weighted-Average Grant Date Fair Value per Share, Beginning balance | $ / shares	$ 0
Weighted-Average Grant Date Fair Value per Share, Granted | $ / shares	3.10
Weighted-Average Grant Date Fair Value per Share, Forfeited | $ / shares	3.10
Weighted-Average Grant Date Fair Value per Share, Ending balance | $ / shares	$ 3.10

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Tax Rates and Effective Tax Rates (Detail)	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statutory rate	21.00%	21.00%	21.00%
Valuation allowance		(32.65%)	(28.74%)
Federal tax rate change		0.00%	0.31%
Other		2.53%	0.01%
Effective tax rate		(0.04%)	0.01%
Predecessor Company [Member]
Statutory rate		21.00%	21.00%	34.00%
Valuation allowance		6.10%	(25.20%)	51.50%
Federal tax rate change				(93.30%)
General business credits		(2.90%)	6.20%	10.80%
Expiration of stock options		(21.40%)
Other		(2.80%)	(2.00%)	(3.00%)
Effective tax rate		0.00%	0.00%	0.00%

Collaboration and License Agr_3

Collaboration and License Agreements - Additional Information (Detail) - Predecessor Company [Member] - USD ($)	Dec. 05, 2018	Feb. 15, 2017	Dec. 31, 2016	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 05, 2017
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration and license agreement termination period						Sep. 30, 2019
Conversion of convertible note payable							$ 13,729,000
Cumulative catch-up adjustment in revenue				$ 4,600,000
Novartis [Member] | Convertible Promissory Note [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, interest rate		6.00%
Debt instrument, maturity date		Dec. 31, 2019
Debt instrument, conversion price percentage		120.00%
Principal amount of note issued		$ 15,000,000
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	288,251
Conversion price	$ 57.70
Collaborative Arrangement [Member] | Novartis [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable payment received			$ 50,000,000
Proceeds from option exercised								$ 7,000,000
Collaboration and license agreement termination period						Sep. 30, 2019
Maximum milestone payments to be received upon achievement of certain milestones			$ 650,000,000
Percentage of observational study costs			50.00%
Assumed percentage of observational study costs upon completion of ongoing Phase 2b trails			100.00%
Collaborative Arrangement [Member] | Novartis [Member] | Scenario Forecast [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Future milestone payments					$ 150,000,000
Investment Agreement [Member] | Novartis [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, maximum borrowing capacity			$ 15,000,000
Debt instrument, interest rate			6.00%
Debt instrument, maturity date			Dec. 31, 2019
Investment Agreement [Member] | Novartis [Member] | Convertible Promissory Note [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, conversion price percentage		120.00%
Number of days trailing average closing price of common stock immediately prior to the conversion date		20 days
Principal amount of note issued		$ 15,000,000
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	288,251
Conversion price	$ 57.70

Collaboration and License Agr_4

Collaboration and License Agreements - Summary of Reconciliation of Deferred Revenue Related to Collaboration Agreement (Detail) - Predecessor Company [Member] - Collaborative Arrangement [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Balance	$ 12,890	$ 26,691
Cumulative effect of adoption of accounting standard		1,299
Additions to deferred revenue	8,826	18,486
Revenue recognized	$ (21,716)	(33,586)
Balance		$ 12,890

Collaboration and License Agr_5

Collaboration and License Agreements - Summary of Reconciliation of Deferred Costs Related To Collaboration Agreement (Detail) - Collaborative Arrangement [Member] - Predecessor Company [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Balance	$ 310
Cumulative effect of adoption of accounting standard		$ 687
Costs recognized	$ (310)	(377)
Balance		$ 310

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - Predecessor Company [Member] - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Defined contribution plan, Employees voluntary contributions, Amount	$ 192,000	$ 239,000	$ 217,000
Eligibility criteria for employees to participate in the plan	Employees are eligible to participate in the plan beginning on the first day of employment.

Commitments - Schedule of ROU A

Commitments - Schedule of ROU Assets and Liabilities Related to Lease and First Lease Amendment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 01, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
ROU assets (included in other assets)	$ 4,334	$ 4,500	$ 619	$ 95
Current portion of lease liabilities	0			108
Total lease liabilities	$ 4,749	$ 4,500	$ 707	108
Predecessor Company [Member]
ROU assets (included in other assets)				221	$ 600
Current portion of lease liabilities				338
Total lease liabilities				$ 338	$ 700

Commitments - Schedule of Undis

Commitments - Schedule of Undiscounted Cash Flows for Operating Lease Liabilities Recorded in Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 01, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Total lease payments	$ 9,026			$ 108
Present value adjustment	(4,277)			0
Total lease liabilities	$ 4,749	$ 4,500	$ 707	108
Predecessor Company [Member]
Total lease payments				351
Present value adjustment				(13)
Total lease liabilities				$ 338	$ 700

Commitments - Schedule of Rent

Commitments - Schedule of Rent Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating lease	$ 570
Predecessor Company [Member]
Operating lease	378	$ 378	$ 378
Short-term leases	68	27
Total	$ 446	$ 405	$ 378

Quarterly Financial Data - Summ

Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effect of Fourth Quarter Events [Line Items]
Total revenues	$ 495			$ 314														$ 1,581	$ 9,893	$ 11,454	$ 1,777
Total operating expenses	3,841			2,060														16,931	10,683	$ 14,772	$ 7,418
Total other income	$ 83			$ 48														$ 55	$ 113
Net loss per share, basic and diluted	$ (0.27)			$ (0.51)														$ (2.06)	$ (0.20)	$ (0.13)	$ (0.27)
Predecessor Company [Member]
Effect of Fourth Quarter Events [Line Items]
Total revenues		$ 526		$ 3,376		$ 10,791		$ 7,024		$ 7,409		$ 7,666		$ 8,774		$ 9,737				$ 21,717	$ 33,586	$ 35,377
Total operating expenses		3,371		6,759		11,619		11,974		11,414		12,324		13,331		14,794				33,723	51,863	52,927
Total other income		116		130		172		203		99		69		60		39				621	267	154
Net loss		$ (2,729)		$ (3,253)		$ (656)		$ (4,747)		$ (3,906)		$ (4,589)		$ (4,497)		$ (5,018)				$ (11,385)	$ (18,010)	$ (17,396)
Net loss per share, basic and diluted		$ (0.82)	[1]	$ (0.98)	[1]	$ (0.20)	[1]	$ (1.43)	[1]	$ (1.26)	[1]	$ (1.52)	[1]	$ (1.49)	[1]	$ (1.67)	[1]			$ (3.43)	$ (5.93)	$ (6.08)
[1]	Net loss per share is computed independently for each quarter and the full year based upon respective shares outstanding; therefore, the sum of the quarterly net loss per share amounts may not equal the annual amounts reported.

Restructuring Costs - Additiona

Restructuring Costs - Additional Information (Detail) - Predecessor Company [Member] - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019
Restructuring Cost and Reserve [Line Items]
Accrued severance liability			$ 0.1
Employee Severance [Member] | Operating Expense [Member]
Restructuring Cost and Reserve [Line Items]
Severance expenses	$ 0.9	$ 1.2
Stock Compensation Expense [Member] | Operating Expense [Member]
Restructuring Cost and Reserve [Line Items]
Increase in noncash stock compensation expenses	$ 0.3	$ 0.3