XML 82 R55.htm IDEA: XBRL DOCUMENT
v3.20.4

Net Loss Per Share Attributable to Common Stockholders - Additional Information (Details) - shares | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jul. 31, 2019 | Dec. 31, 2020
Series C Convertible Preferred Stock | Maximum |  |
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] |  |
Convertible preferred stock could have been issued | 17,014,902 | 17,014,902

X
- Definition Temporary equity stock issued additional during period shares new issues. + References No definition available. + Details
Name: | gray_TemporaryEquityStockIssuedAdditionalDuringPeriodSharesNewIssues
Namespace Prefix: | gray_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition 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. + References No definition available. + Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=gray_SeriesCConvertiblePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |