Reverse Recapitalization (Details)			1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 25, 2021 USD ($) $ / shares shares	Jun. 23, 2021 shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2020 shares	Sep. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2021 USD ($) shares	Sep. 30, 2021 USD ($) $ / shares shares	Jun. 24, 2021 $ / shares shares	Mar. 31, 2021 shares	Dec. 31, 2020 $ / shares shares	Dec. 10, 2020 USD ($)	Aug. 20, 2020 shares
Change in Net Cash and Net Assets in Reverse Recapitalization
Forum cash and cash equivalents | $	$ 250,258,000
Less redemptions of Class A common stock units | $						$ (61,000)
PIPE investment proceeds | $	130,000,000
Less cash paid to underwriters and other transaction costs | $	(25,717,000)
Net change in cash and cash equivalent and restricted cash as a result of recapitalization | $	243,769,000		$ 0				$ 243,769,000
Prepaid expenses and other current assets | $	17,000
Accounts payable and other | $	(326,000)
Warrant liabilities | $	(20,392,000)
Change in net assets as a result of recapitalization | $	$ 223,068,000
Change in Shares Outstanding in Reverse Recapitalization
Common shares outstanding	118,777,012				118,777,012		118,777,012			82,117,288
Common shares issued to PIPE investors	13,000,000
Common shares issued	5,000,000
Common shares outstanding immediately after Business Combination	111,024,789
Common shares issued upon conversion of ELM Convertible Notes	2,752,223
Transaction costs | $	$ 26,100,000
Transaction costs recorded in additional paid-in capital | $	25,700,000
Related party receivable | $	$ 17,000
Exchange ratio	821.17
Common stock par value (in dollars per share) | $ / shares					$ 0.0001		$ 0.0001			$ 0.0001
Capital stock authorized (in shares)	1,100,000,000							111,000,000
Common stock authorized (in shares)	1,000,000,000				1,000,000,000		1,000,000,000			1,000,000,000
Preferred stock authorized (in shares)	100,000,000				100,000,000		100,000,000	1,000,000		100,000,000
Preferred stock par value (in dollars per share) | $ / shares					$ 0.0001		$ 0.0001	$ 0.0001		$ 0.0001
Increase in common stock authorized (in shares)	890,000,000
Increase in preferred stock authorized (in shares)	99,000,000
Outstanding principal converted | $							$ 27,522,000
Interest expense | $			$ 0		$ 656,000		$ 3,126,000
Common Stock
Change in Net Cash and Net Assets in Reverse Recapitalization
Less redemptions of Class A common stock units | $						$ (1,000)
Change in Shares Outstanding in Reverse Recapitalization
Common shares outstanding			821,173	821,173	118,777,012	118,777,012	118,777,012		82,117,288	82,117,288		0
Repurchase of common stock (in shares)		5,006,691				5,006,691
Common shares issued to PIPE investors				1,000
Common shares issued						5,000,000
Common shares issued upon conversion of ELM Convertible Notes						2,752,223
SERES Asset Purchase
Change in Shares Outstanding in Reverse Recapitalization
Number of shares required to be delivered (in shares)	5,000,000
Purchase consideration delivered | $	$ 49,950,000
ELM Convertible Notes | Convertible Promissory Notes
Change in Shares Outstanding in Reverse Recapitalization
Principal amount | $											$ 25,000,000
Outstanding principal converted | $	$ 25,000,000
Debt conversion ratio	0.90909
Debt conversion, price per share (in dollars per share) | $ / shares	$ 10.00
Interest expense | $							$ 2,400,000
Class B common stock
Change in Shares Outstanding in Reverse Recapitalization
Common stock par value (in dollars per share) | $ / shares	0.0001
Common stock authorized (in shares)								10,000,000
Class A common stock
Change in Shares Outstanding in Reverse Recapitalization
Common stock par value (in dollars per share) | $ / shares	$ 0.0001
Common stock authorized (in shares)								100,000,000
PIPE
Change in Shares Outstanding in Reverse Recapitalization
Number of shares issued (in shares)	13,000,000
Price per share (in dollars per share) | $ / shares	$ 10.00
Aggregate purchase price | $	$ 130,000,000
ELM Shareholders
Change in Shares Outstanding in Reverse Recapitalization
Common shares issued	77,110,597
Shares converted in exchange (in shares)	93,903
Forum
Change in Net Cash and Net Assets in Reverse Recapitalization
Less redemptions of Class A common stock units | $	$ (110,772,000)
Change in Shares Outstanding in Reverse Recapitalization
Common shares outstanding								31,991,250
Repurchase of common stock (in shares)	11,077,058