Name:	rytm_AccruedPayrollRelatedExpenseCurrent
Namespace Prefix:	rytm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of expenses incurred but not yet paid related to research and development, due within one year or the normal operating cycle, if longer.

No definition available.

Name:	rytm_AccruedResearchAndDevelopmentCosts
Namespace Prefix:	rytm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying value as of the balance sheet date of obligations incurred through that date and payable for royalties.

No definition available.

Name:	rytm_RoyaltiesCurrent
Namespace Prefix:	rytm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying value as of the balance sheet date of obligations incurred through that date and payable for sales allowances.

No definition available.

Name:	rytm_SalesAllowancesAccruedCurrent
Namespace Prefix:	rytm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Name:	us-gaap_AccruedLiabilitiesCurrent
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Data Type:	xbrli:monetaryItemType
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Carrying value as of the balance sheet date of obligations incurred through that date and payable for professional fees, such as for legal and accounting services received. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Name:	us-gaap_AccruedProfessionalFeesCurrent
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer.

Name:	us-gaap_OtherAccruedLiabilitiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.