Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Feb. 22, 2023	Jun. 30, 2022
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2022
Entity File Number	001-38223
Entity Registrant Name	RHYTHM PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-2159271
Entity Address, Address Line One	222 Berkeley Street
Entity Address, Address Line Two	12th Floor
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02116
City Area Code	857
Local Phone Number	264-4280
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	RYTM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 188.4
Entity Common Stock, Shares Outstanding		56,747,577
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Central Index Key	0001649904
Amendment Flag	false
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Boston, Massachusetts