Number of common shares whose milestone were achieved by the company.

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Number of stock options modified under share-based payment arrangement during the period.

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Amount of share based compensation arrangement by share based payment award unrecognized compensation costs.

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Number of shares or units withheld to cover taxes, under share-based payment arrangement.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Aggregate number of common shares reserved for future issuance.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Price of a single share of a number of saleable stocks of a company.

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Number of shares for which recognition of cost was accelerated for award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Value, after forfeiture, of shares issued under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).

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Share-Based Compensation - Additional Information (Details) - USD ($)		1 Months Ended			3 Months Ended
	Mar. 27, 2020	Jun. 30, 2020	Mar. 31, 2020	Feb. 29, 2020	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense				$ 70,000,000	$ 130,000	$ 588,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense				4,000,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized					243,532
Share Based Compensation Arrangement By Share Based Payment Award Unrecognized Compensation Costs					$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number					338,663
Allocated Share-based Compensation Expense					$ 800,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number					338,663
Number of options outstanding at September 30, 2020					338,663
Common Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	9,795		35,000
Allocated Share-based Compensation Expense			$ 74,800,000
Number of awards issued	9,795		35,000
Number of common shares whose milestone were achieved	15,000
Number of fully vested shares withheld	5,205
Expense to be recognized upon the achievement of certain milestones			$ 65,200,000			$ 65,200,000
Chief Financial Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense				153,000,000
Stock options issued				$ 80,000,000
Number of options to purchase common stock modified				236,970
Chief Financial Officer [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of awards whose vesting was accelerated				3,300
Biostage Amended and Restated Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period					10 years
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized		3,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized		5,098,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized					$ 300,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition					3 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value					$ 0
Share Price					$ 1.34
Shares available for issuance					3,461,091