Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Document information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	001-38492
Entity Registrant Name	Kiniksa Pharmaceuticals, Ltd.
Entity Incorporation, State or Country Code	D0
Entity Tax Identification Number	98-1327726
Entity Address, Address Line One	Clarendon House
Entity Address, Address Line Two	2 Church Street
Entity Address, City or Town	Hamilton
Entity Address, Country	BM
Entity Address, Postal Zip Code	HM11
City Area Code	808
Local Phone Number	189-6257
Title of 12(b) Security	Class A Common Shares
Trading Symbol	KNSA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 712.6
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001730430
Amendment Flag	false
Common Shares
Document information
Entity Common Stock, Shares Outstanding		68,232,304
Class A common shares
Document information
Entity Common Stock, Shares Outstanding		31,922,546
Class B common shares
Document information
Entity Common Stock, Shares Outstanding		2,227,614
Class A1 common shares
Document information
Entity Common Stock, Shares Outstanding		18,024,526
Class B1 common shares
Document information
Entity Common Stock, Shares Outstanding		16,057,618