Note 11 - Forbearance Agreement and Convertible Note (Details Textual) - USD ($)		3 Months Ended		6 Months Ended	9 Months Ended
	May 17, 2023	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Sep. 30, 2023	Sep. 30, 2022
Forbearance Agreement, Deferred Accounts Payable	$ 11,800,000
Forbearance Agreement, Deferred Accounts Payable, Monthly Payments	250,000
Deferred Accounts Payable, Fair Value	$ 7,900,000
Gain (Loss) on Extinguishment of Debt		$ 0	$ 0		$ 2,611,000	$ (0)
Paid-in-Kind Interest					568,000	0
Change in Fair Value of Note Payables		(3,832,000)	(0)		(3,192,000)	0
Forbearance Agreement, Deferred Accounts Payable, Payment Term (Month)	48 months
Forbearance Agreement, Deferred Accounts Payable, Cash Payment Not Paid When Due Subject to Interest Rate	10.00%
Forbearance Agreement, Deferred Accounts Payable, Cash Payment Due Benchmark Period (Day)	60 days
OCI, Market Risk Benefit, Instrument-Specific Credit Risk, Gain (Loss), after Adjustments and Tax, Parent		1,208,000	$ 0		1,208,000	$ 0
Convertible Debt [Member] \| Supplier [Member]
Debt Instrument, Face Amount	$ 15,000,000
Gain (Loss) on Extinguishment of Debt	$ 2,600,000
Debt Instrument, Interest Rate, Stated Percentage	10.00%
Debt Instrument, Event of Default, Payment	$ 3,000,000
Debt Instrument, Event of Default, Interest Rate	14.00%
Debt Instrument, Convertible, Beneficial Ownership Limitation	19.99%
Debt Instrument, Convertible, Conversion Price (in dollars per share)	$ 1.3
Debt Conversion, Converted Instrument, Shares Issued (in shares)	11,538,461
Debt Instrument, Convertible, Conversion Period After Date of Issuance (Month)	18 months
Debt Issuance Costs, Net	$ 16,679
Notes Payable, Fair Value Disclosure		$ 10,800,000		$ 15,800,000	10,800,000
Paid-in-Kind Interest				200,000	400,000
Change in Fair Value of Note Payables				600,000
Debt Instrument, Event of Default, Percentage of Principal for Acceleration of Maturity	100.00%
Debt Instrument, Event of Default, Percentage of Principal Automatically and Immediately Due	100.00%
Debt Instrument, Event of Default, Judgement Payment Rendered Against Company	$ 3,000,000
OCI, Market Risk Benefit, Instrument-Specific Credit Risk, Gain (Loss), after Adjustments and Tax, Parent					1,200,000
Convertible Debt [Member] \| Supplier [Member] \| Other Nonoperating Income (Expense) [Member]
Fair Value, Option, Changes in Fair Value, Gain (Loss)				$ 800,000	$ 3,800,000

ATHERSYS, INC / NEW 10-Q