Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 28, 2022	Jun. 30, 2021
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-34516
Entity Registrant Name	Cowen Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-0423711
Entity Address, Address Line One	599 Lexington Avenue
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10022
City Area Code	646
Local Phone Number	562-1010
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1,142,196,218
Entity Common Stock, Shares Outstanding		27,458,549
Documents Incorporated by Reference	Documents incorporated by reference:Part III of this Annual Report on Form 10-K incorporates by reference information (to the extent specific sections are referred to herein) from the Registrant's Proxy Statement for its 2022 Annual Meeting of Stockholders.
Entity Central Index Key	0001466538
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Auditor Name	KPMG LLP
Auditor Location	New York, NY
Auditor Firm ID	185
Class A Common Stock, par value $0.01 per share | The Nasdaq Global Market
Entity Information [Line Items]
Title of 12(b) Security	Class A Common Stock, par value $0.01 per share
Trading Symbol	COWN
Security Exchange Name	NASDAQ
7.75% Senior Notes due 2033 | The Nasdaq Global Market
Entity Information [Line Items]
Title of 12(b) Security	7.75% Senior Notes due 2033
Trading Symbol	COWNL
Security Exchange Name	NASDAQ