Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 05, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	001-38128
Entity Registrant Name	Checkpoint Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-2568632
Entity Address, Address Line One	2 Gansevoort Street
Entity Address, Address Line Two	9th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10014
City Area Code	781
Local Phone Number	652-4500
Title of 12(b) Security	Common Stock, par value $0.0001 per
Trading Symbol	CKPT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Central Index Key	0001651407
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Public Float			$ 80,720,490
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
IcfrAuditorAttestationFlag	false
Common Shares [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		68,212,354
Class A Common Shares [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		7,000,000