Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Computation of earnings per share:
Net income (loss)	$ 303,991	$ 207,064	$ 55,870
Net income (loss) attributable to non-controlling interests in consolidated subsidiaries and investment funds	8,380	(9,299)	31,239
Net income (loss) attributable to Cowen Inc.	295,611	216,363	24,631
Preferred stock dividends	6,792	6,792	6,792
Net income (loss) attributable to Cowen Inc. common stockholders	$ 288,819	$ 209,571	$ 17,839
Shares for basic and diluted calculations:
Weighted average shares used in basic computation, shares	27,721,000	27,790,000	29,525,000
Weighted average shares used in diluted computation, shares	32,628,000	29,519,000	31,286,000
Earnings (loss) per share:
Earnings Per Share, Basic (in dollars per share)	$ 10.42	$ 7.54	$ 0.60
Earnings Per Share, Diluted (in dollars per share)	$ 8.85	$ 7.10	$ 0.57
Convertible Debt
Shares for basic and diluted calculations:
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	1,404,000	0	0
Restricted Stock
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares	2,748,000	1,644,000	1,735,000
Restricted Stock | Quarton
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares	0	85,000	26,000
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		334,230
Performance based restricted stock
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares	755,000	0	0
Common Stock Class A
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Common stock, shares outstanding, shares	27,778,964	26,845,628
Common stock, restricted shares, shares	972,732
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	334,230