Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Computation of earnings per share:
Net income (loss)	$ 55,147	$ 152,066
Net income (loss) attributable to non-controlling interests in consolidated subsidiaries and investment funds	20,131	4,562
Net income (loss) attributable to Cowen Inc.	35,016	147,504
Preferred stock dividends	1,698	1,698
Net income (loss) attributable to Cowen Inc. common stockholders	33,318	145,806
Dilutive Securities, Effect on Basic Earnings Per Share	41	0
Net Income (Loss) Available to Common Stockholders, Diluted	$ 33,359	$ 145,806
Shares for basic and diluted calculations:
Weighted average shares used in basic computation, shares	28,386,000	27,359,000
Weighted average shares used in diluted computation, shares	31,772,000	33,565,000
Earnings (loss) per share:
Earnings Per Share, Basic (in dollars per share)	$ 1.17	$ 5.33
Earnings Per Share, Diluted (in dollars per share)	$ 1.05	$ 4.34
Convertible Debt
Shares for basic and diluted calculations:
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	0	2,659,000
Convertible Preferred Stock
Shares for basic and diluted calculations:
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	708,000	0
Restricted Stock
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares	2,222,000	3,102,000
Restricted Stock | Quarton
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares	82,000	0
Restricted Stock Units (RSUs) | Equity Plans
Shares for basic and diluted calculations:
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number			972,732
Performance based restricted stock
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares	374,000	445,000
Common Stock Class A
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Common stock, shares outstanding, shares	27,614,903		27,778,964
Common stock, restricted shares, shares	246,803
Common Stock Class A | Restricted Stock
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Common stock, shares outstanding, shares	901,374		901,374