Cowen (COWN) 10-K 6 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 05, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	Cowen Inc.
Entity Central Index Key	1,466,538
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		28,985,051
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 476,392,881

Consolidated Statements of Fina

Consolidated Statements of Financial Condition - USD ($)	Dec. 31, 2017		Dec. 31, 2016
Assets
Cash and cash equivalents	$ 130,052,000		$ 110,990,000
Cash collateral pledged	17,888,000		13,342,000
Segregated Cash	116,268,000		1,024,000
Securities owned, at fair value	673,221,000		700,876,000
Receivable on derivative contracts, at fair value	69,177,000		22,901,000
Securities Borrowed	443,148,000		0
Other investments	141,548,000		157,279,000
Deposits with clearing organizations, brokers and banks	93,996,000		8,939,000
Receivable from brokers, dealers and clearing organizations	508,178,000		78,898,000
Receivables from Customers, net of allowance of $1,550 and $0, respectively	49,891,000		0
Fees receivable, net of allowance of $1,736 and $0, respectively	111,784,000		45,883,000
Due from related parties	34,814,000		39,629,000
Fixed assets, net of accumulated depreciation and amortization of $28,355 and $23,867, respectively	40,496,000		42,408,000
Goodwill	60,678,000		60,678,000
Intangible assets, net of accumulated amortization of $33,081 and $29,418, respectively	29,955,000		25,769,000
Deferred tax assets, net	116,323,000		165,656,000
Other assets	88,268,000		38,406,000
Consolidated Funds
Cash and cash equivalents	21,988,000		17,761,000
Securities owned, at fair value	165,916,000		79,237,000
Receivable on derivatives, Consolidated Funds	2,520,000		893,000
Other investments	374,111,000		401,465,000
Receivable from brokers, Consolidated Funds	5,644,000		5,978,000
Other assets	388,000		511,000
Total Assets	3,296,252,000		2,018,523,000
Liabilities
Securities sold, not yet purchased, at fair value	342,527,000		266,090,000
Payable for derivative contracts, at fair value	42,750,000		20,762,000
Securities Loaned	456,831,000		0
Payable to brokers, dealers and clearing organizations	252,153,000		210,309,000
Payables to Customers	352,467,000		0
Commission management payable	70,451,000		3,590,000
Compensation payable	150,206,000		98,084,000
Notes payable and other debt	173,458,000		77,030,000
Convertible debt	141,502,000		130,029,000
Fees payable	8,047,000		3,272,000
Due to related parties	570,000		573,000
Accounts payable, accrued expenses and other liabilities	96,533,000		47,525,000
Consolidated Funds
Securities sold, not yet purchased, at fair value, Consolidated Funds	0	[1]	883,000
Payable for derivative contracts, at fair value, Consolidated Funds	7,130,000		572,000
Payable to brokers, Consolidated Funds	751,000		3,700,000
Contributions received in advance	0		2,000,000
Capital withdrawals payable	11,931,000		1,408,000
Accounts payable, accrued expenses and other liabilities	322,000		841,000
Total Liabilities	2,107,629,000		866,668,000
Commitments and Contingencies
Redeemable non-controlling interests	440,604,000		379,205,000
Stockholders' equity
Additional paid-in capital	1,004,664,000		928,646,000
(Accumulated deficit) retained earnings	(70,116,000)		(2,442,000)
Accumulated other comprehensive income (loss)	(8,000)		(2,000)
Less: Class A common stock held in treasury, at cost, 10,593,191 and 9,810,802 shares as of June 30, 2017 and December 31, 2016, respectively.	(186,846,000)		(153,845,000)
Total Stockholders' Equity	748,019,000		772,650,000
Total Liabilities and Stockholders' Equity	3,296,252,000		2,018,523,000
Convertible Preferred Stock
Stockholders' equity
Preferred stock	1,000		1,000
Common Stock Class A
Stockholders' equity
Common stock	324,000		292,000
Less: Class A common stock held in treasury, at cost, 10,593,191 and 9,810,802 shares as of June 30, 2017 and December 31, 2016, respectively.	(186,846,000)		(153,845,000)
Common Stock Class B
Stockholders' equity
Common stock	$ 0		$ 0
[1]	As of December 31, 2016, maturities ranged from September 2019 to September 2023 and interest rates ranged from 4.38% to 9.25%.

Consolidated Statements of Fin3

Consolidated Statements of Financial Condition (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Allowance for Uncollectible Customer's Liability for Acceptances	$ 1,550,000	$ 0
Allowance for Doubtful Accounts Receivable, Current	1,736,000	0
Assets
Fixed assets, accumulated depreciation and amortization (in dollars)	28,355,000	23,867,000
Intangible assets, accumulated amortization (in dollars)	$ 33,081,000	$ 29,418,000
Stockholders' equity
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	120,750	120,750
Preferred stock, shares outstanding	120,750	120,750
Preferred Stock, Liquidation Preference, Value	$ 120,750,000	$ 120,750,000
Common stock, shares authorized	125,000,000
Treasury Stock, Shares	12,133,276	9,810,802
Common Stock Class A
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	62,500,000	62,500,000
Common stock, shares issued	41,765,296	36,542,091
Common stock, shares outstanding	29,632,020	26,731,289
Common stock, restricted shares	191,962	162,176
Treasury Stock, Shares	12,133,276	9,810,802
Common Stock Class B
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	62,500,000	62,500,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Investment banking		$ 223,614	$ 133,279	$ 222,781
Brokerage		293,610	199,180	157,722
Management fees		33,245	40,612	41,906
Incentive income		5,383	8,334	1,466
Interest and dividends		49,440	14,732	13,796
Reimbursement from affiliates		2,860	10,504	21,557
Aircraft lease revenue		3,751	4,161	0
Reinsurance premiums		30,996	32,459	0
Other revenue		8,561	22,355	3,726
Consolidated Funds
Interest and dividends		5,870	4,792	1,086
Other revenues		1,451	1,157	527
Total revenues		658,781	471,565	464,567
Expenses
Employee compensation and benefits		404,087	310,038	321,386
Floor brokerage and trade execution		75,601	32,286	27,460
Interest and dividends		60,949	29,308	26,220
Professional, advisory and other fees		31,942	23,190	25,578
Service fees		14,999	7,918	7,535
Communications		23,460	17,768	14,325
Occupancy and equipment		35,184	32,286	29,055
Depreciation and amortization		13,078	12,713	9,498
Client services and business development		28,327	27,828	25,413
Reinsurance claims, commissions and amortization of deferred acquisition costs		30,486	29,904	0
Restructuring Costs		8,763	0	0
Other Expenses		18,196	14,815	15,594
Consolidated Funds
Interest and dividends		9,836	6,434	1,104
Professional, advisory and other fees		1,145	1,148	654
Floor brokerage and trade execution		318	431	51
Other expenses		1,227	1,051	501
Total expenses		757,598	547,118	504,374
Other income (loss)
Net gains (losses) on securities, derivatives and other investments		76,179	23,381	36,789
Bargain purchase gain, net of tax		6,914	0	0
Gain (Loss) on Extinguishment of Debt		(16,039)	0	0
Consolidated Funds
Net realized and unrealized gains (losses) on investments and other transactions		19,660	7,085	12,517
Net realized and unrealized gains (losses) on derivatives		19,476	13,503	2,071
Net gains (losses) on foreign currency transactions		(411)	97	(91)
Total other income (loss)		105,779	44,066	51,286
Income (loss) before income taxes		6,962	(31,487)	11,479
Income tax expense (benefit)		44,053	(19,092)	(47,496)
Net income (loss)		(37,091)	(12,395)	58,975
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds		(23,791)	(6,882)	(15,246)
Net income (loss) attributable to Cowen Inc.		(60,882)	(19,277)	43,729
Preferred stock dividends		6,792	6,792	4,075
Net income (loss) attributable to Cowen Group, Inc. common stockholders		$ (67,674)	$ (26,069)	$ 39,654
Weighted average common shares outstanding:
Basic (in shares)	[1]	29,492	26,857	27,522
Diluted (in shares)	[1]	29,492	26,857	29,043
Earnings (loss) per share:
Earnings Per Share, Basic (in dollars per share)	[1]	$ (2.29)	$ (0.97)	$ 1.44
Earnings Per Share, Diluted (in dollars per share)	[1]	$ (2.29)	$ (0.97)	$ 1.37
[1]	Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (37,091)	$ (12,395)	$ 58,975
Other comprehensive income (loss), net of tax:
Foreign currency translation	(6)	(2)	(17)
Total other comprehensive income, net of tax	(6)	(2)	(17)
Comprehensive income (loss)	$ (37,097)	$ (12,397)	$ 58,958

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Treasury Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings/(Accumulated deficit)	Common Stock Class A	Preferred Stock	Convertible Preferred StockRetained Earnings/(Accumulated deficit)	Call Option
Balance at Dec. 31, 2014	$ 677,675	$ (79,771)	$ 773,166	$ 17	$ (16,027)	$ 290	$ 0
Common Stock, Shares, Outstanding at Dec. 31, 2014						27,922,799
Preferred stock, shares outstanding at Dec. 31, 2014							0
Redeemable Noncontrolling Interest at Dec. 31, 2014	86,076
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Inc.	43,729				43,729
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	15,246
Foreign currency translation	(17)			(17)
Capital contributions	110,178
Capital withdrawals	(24,589)
Common stock issuance upon acquisition, shares						137,156
Common stock issuance upon close of acquisition (see Note 2)	3,008		3,006			$ 2
Restricted stock awards issued, shares						1,068,227
Purchase of treasury stock, at cost, shares						(2,752,019)
Purchase of treasury stock, at cost	(57,585)	(57,585)
Preferred stock dividends (See Note 24)	(4,075)							$ (4,100)
Preferred stock issuance, net of issuance costs, shares							120,750
Preferred stock issuance, net of issuance costs	117,195		117,194				$ 1
Preferred Stock Dividends								(4,075)
Capped call option transaction			(15,878)						$ (15,878)
Stock Options exercised, shares						25,000
Stock options exercised, value	395		395
Income tax effect from share based compensation	3,806		3,806
Amortization of share based compensation	21,740		21,740
Balance at Dec. 31, 2015	789,993	(137,356)	903,429	0	23,627	$ 292	$ 1
Common Stock, Shares, Outstanding at Dec. 31, 2015						26,401,163
Preferred stock, shares outstanding at Dec. 31, 2015							120,750
Redeemable Noncontrolling Interest at Dec. 31, 2015	186,911
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Inc.	(19,277)				(19,277)
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	6,882
Foreign currency translation	(2)			(2)
Capital contributions	276,923
Capital withdrawals	(18,469)
Common stock issuance upon close of acquisition (see Note 2)	0
Deconsolidation of funds	(73,042)
Restricted stock awards issued, shares						1,511,995
Purchase of treasury stock, at cost, shares						(1,181,869)
Purchase of treasury stock, at cost	(16,489)	(16,489)
Preferred stock dividends (See Note 24)	(6,792)							(6,800)
Preferred Stock Dividends								(6,792)
Income tax effect from share based compensation	(822)		(822)
Amortization of share based compensation	26,039		26,039
Balance at Dec. 31, 2016	$ 772,650	(153,845)	928,646	(2)	(2,442)	$ 292	$ 1
Common Stock, Shares, Outstanding at Dec. 31, 2016						26,731,289
Preferred stock, shares outstanding at Dec. 31, 2016	120,750						120,750
Redeemable Noncontrolling Interest at Dec. 31, 2016	$ 379,205
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to Cowen Inc.	(60,882)				(60,882)
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	23,791
Foreign currency translation	(6)			(6)
Capital contributions	119,112
Capital withdrawals	(81,504)
Common stock issuance upon acquisition, shares						3,162,278
Common stock issuance upon close of acquisition (see Note 2)	47,607		47,575			$ 32
Restricted stock awards issued, shares						2,060,927
Purchase of treasury stock, at cost, shares						(2,322,474)
Purchase of treasury stock, at cost	(33,001)	(33,001)
Preferred stock dividends (See Note 24)	(6,792)							$ (6,792)
Amortization of share based compensation	28,443		28,443
Balance at Dec. 31, 2017	$ 748,019	$ (186,846)	$ 1,004,664	$ (8)	$ (70,116)	$ 324	$ 1
Common Stock, Shares, Outstanding at Dec. 31, 2017						29,632,020
Preferred stock, shares outstanding at Dec. 31, 2017	120,750						120,750
Redeemable Noncontrolling Interest at Dec. 31, 2017	$ 440,604

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income (loss)	$ (37,091)	$ (12,395)	$ 58,975
Adjustments to reconcile net income (loss) to net cash provided by / (used in) operating activities:
Bargain purchase gain, net of tax	(6,914)	0	0
Depreciation and amortization	13,078	12,713	9,498
Net gain on sale of divested business	0	(15,638)	0
Amortization of Debt Issue Costs	1,261	1,208	1,163
Amortization of debt discount	7,435	6,885	6,302
Gain / (loss) on extinguishment of debt	10,551	0	0
Tax benefits (expense) from share based payment arrangements	0	(822)	3,806
Share-based compensation	28,443	26,039	21,740
Deferred tax benefit	45,856	(21,274)	(17,966)
Deferred rent obligations	(2,192)	(880)	(2,333)
Net loss (gain) on disposal of fixed assets	(2,346)	0	54
Contingent liability adjustment	0	2,139	(200)
Purchases of securities owned, at fair value	(4,943,394)	(4,483,975)	(5,856,112)
Proceeds from sales of securities owned, at fair value	5,131,938	4,447,094	6,039,719
Proceeds from sales of securities sold, not yet purchased, at fair value	2,455,876	3,016,934	2,730,939
Payments to cover securities sold, not yet purchased, at fair value	(2,444,010)	(3,054,869)	(2,674,153)
Net (gains) losses on securities, derivatives and other investments	(78,303)	(28,878)	(34,495)
Consolidated Funds
Purchases of securities owned, at fair value	(385,544)	(113,653)	(25,000)
Proceeds from sales of securities owned, at fair value	338,268	73,011	0
Proceeds from sales of securities sold, not yet purchased, at fair value	217	2,226	0
Payments to cover securities sold, not yet purchased, at fair value	(899)	(1,799)	0
Purchases of other investments	(26,206)	(221,897)	(92,305)
Proceeds from sales of other investments	64,867	17,116	31,417
Net realized and unrealized (gains) losses on investments and other transactions	(28,267)	(17,402)	(13,552)
(Increase) decrease in operating assets:
Cash acquired through acquisition	30,562	0	0
Cash collateral pledged	(4,546)	(3,257)	(1,779)
Segregated Cash	13,781	229	(1,253)
Securities owned, at fair value, held at broker dealer	(102,137)	(17,005)	14,877
Receivable on derivative contracts, at fair value	(46,277)	16,717	10,259
Securities Borrowed	(184,827)	0	676,100
Deposits with clearing organizations, brokers and banks	(32,460)	(1,874)	(6,965)
Receivable from brokers, dealers and clearing organizations	(366,297)	31,795	(20,785)
Receivable from customers, net of allowance	(6,422)	0	0
Fees receivable, net of allowance	(29,669)	(12,632)	11,099
Due from related parties	4,815	(176)	(13,344)
Other assets	(33,454)	(10,048)	4,580
Consolidated Funds
Cash and cash equivalents	(4,227)	(3,827)	(13,433)
Receivable on derivative contracts, at fair value	(1,627)	(893)	0
Receivable from brokers	334	(5,978)	0
Other assets	123	152	770
Increase (decrease) in operating liabilities:
Securities sold, not yet purchased, at fair value, held at broker dealer	19,226	7,160	(11,747)
Payable for derivative contracts, at fair value	(1,399)	(421)	(20,147)
Securities Loaned	170,472	0	(682,493)
Payable to brokers, dealers and clearing organizations	(32,440)	78,520	(204,186)
Payables to customers	340,666	0	0
Commission management payable	(15,857)	242	2,225
Compensation payable	9,150	(60,279)	5,540
Fees payable	(639)	(2,366)	(693)
Due to related parties	(3)	244	(145)
Accounts payable, accrued expenses and other liabilities	13,046	(9,133)	(5,337)
Consolidated Funds
Contributions received in advance	(2,000)	1,150	850
Payable to brokers	(2,949)	3,699	0
Payable for derivative contracts, at fair value	6,558	572	0
Due to related parties	(189)	453	3
Accounts payable, accrued expenses and other liabilities	(330)	528	(98)
Net cash provided by / (used in) operating activities	(116,392)	(354,545)	(68,605)
Cash flows from investing activities:
Purchases of other investments	(10,419)	(33,786)	(14,149)
Purchase of business	(55,049)	(6,258)	(38,416)
Proceeds from sales of other investments	71,749	54,068	58,166
Loans issued	(13,745)	0	(46,000)
Proceeds from loans held for investments	3,203	42,800	0
Proceeds from divested business, net of cash divested	0	17,303	0
Purchase of fixed assets	(5,986)	(15,613)	(7,030)
Sale of fixed assets	7,850	0	0
Net cash provided by / (used in) investing activities	(2,397)	58,514	(47,429)
Cash flows from financing activities:
Proceeds from Convertible Debt	135,000	0	0
Repayments on convertible debt	(115,140)	0	0
Proceeds from Issuance of Preferred Stock, net of issuance costs	0	0	117,194
Capped call option transaction	0	0	(15,878)
Deferred Debt Issuance Costs	(7,176)	0	0
Borrowings on notes and other debt	171,148	30,638	7,140
Repayments on notes and other debt	(72,757)	(29,800)	(3,299)
Income tax effect from share-based payment arrangements	0	(822)	3,806
Proceeds from Stock Options Exercised	0	0	394
Purchase of treasury stock	(19,662)	(7,654)	(48,678)
Cash paid to acquire net assets (contingent liability payment)	(393)	(2,358)	(1,725)
Capital contributions to redeemable non-controlling interests in operating entities	0	10	5,644
Capital withdrawals to redeemable non-controlling interests in operating entities	(5,178)	(6,995)	(13,860)
Consolidated Funds
Capital contributions by redeemable non-controlling interests in Consolidated Funds	117,812	276,914	104,533
Capital withdrawals to redeemable non-controlling interests in Consolidated Funds	(65,803)	(10,144)	(11,514)
Net cash provided by / (used in) financing activities	137,851	249,789	143,757
Change in cash and cash equivalents	19,062	(46,242)	27,723
Cash and cash equivalents at beginning of period	110,990	157,232	129,509
Cash and cash equivalents at end of period	130,052	110,990	157,232
Interest Paid	26,632	17,540	17,525
Income Taxes Paid	2,172	5,085	4,161
Supplemental information
Conversion option value on 2022 Convertible Notes	23,387	0	0
Purchase of treasury stock, at cost, through net settlement (See Note 24)	11,889	8,835	8,907
Preferred stock dividends declared (See Note 24)	6,792	6,792	4,075
Net assets (liabilities) acquired upon acquisition (net of cash) (See Note 2)	77,790	0	22,468
Common stock issuance upon close of acquisition (see Note 2)	47,607	0	3,008
Notes payable increase through asset acquisition	0	7,164	0
Net assets of deconsolidated entities	0	73,042	0
Conversion of redeemable non-controlling interest to loan receivable	$ 1,299	$ 0	$ 0

Organization and Business

Organization and Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Business	Organization and Business Cowen Inc. (formerly Cowen Group, Inc.), a Delaware corporation formed in 2009, is a diversified financial services firm which, together with its consolidated subsidiaries (collectively, “Cowen,” or the “Company”), operates through its two business segments: investment management and broker-dealer. The Company's investment management segment, includes private funds, managed accounts, commodity pools, real estate funds, private equity structures, registered investment companies and listed vehicles . The Company's broker-dealer segment offers investment banking, research, sales and trading, prime brokerage, global clearing and commission management services to companies and primarily institutional investor clients. The Company's primary target sectors are healthcare, technology, media and telecommunications, information and technology services, consumer, aerospace and defense, industrials, energy and transportation . On December 5, 2016, the Company effected a one-for-four reverse stock split of the Company's common stock. Except where the context indicates otherwise, all share and per share information has been retroactively adjusted to reflect the reverse stock split.

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions Convergex Group On April 2, 2017, the Company, through its wholly owned subsidiary Cowen CV Acquisition LLC, entered into a securities purchase agreement with, among others, Convergex Holdings LLC to acquire all the outstanding interests in Convergex Group, LLC ("Convergex Group") (subsequently renamed to Cowen Execution Holdco LLC) , a provider of agency based execution services and trading technology to middle market institutional investors and broker-dealers . Convergex Group's operations were primarily conducted through two U.S. Securities Exchange Commission ("SEC") registered broker-dealers, Convergex Execution Solutions LLC (subsequently renamed to Cowen Execution Services LLC) ("Cowen Execution") and Westminster Research Associates LLC ("Westminster") and also Convergex Limited (subsequently renamed to Cowen Execution Services Limited) ("Cowen Execution Ltd"), which is based in the United Kingdom and regulated by the Financial Conduct Authority ("FCA"). The purchase price was paid approximately 50% in cash and 50% in Cowen Inc. Class A common stock. The acquisition was consummated effective as of June 1, 2017 . The adjusted aggregate estimated purchase price was $98.0 million , which was determined based on closing date tangible book value of Convergex Group, less certain closing adjustments. A portion of the preliminary purchase price was deposited into escrow as a reserve for any future claims against the sellers of Convergex Group. On closing, the Company paid cash of $48.6 million and issued 3,162,278 of the Company’s Class A common stock determined based on the 30 -day volume-weighted average price per share of $ 15.05 as of May 30, 2017. Subsequent to the closing date, adjustments were identified and the sellers and the Company agreed to settle all of the outstanding closing date adjustments. The acquisition was accounted for under the acquisition method of accounting in accordance with accounting principles generally accepted in the United States of America ("US GAAP"). As such, results of operations for Convergex Group are included in the accompanying consolidated statements of operations since the date of acquisition, and the assets acquired and liabilities assumed were recorded at their fair value as of the acquisition date. Subsequent to the acquisition, the operations of Convergex Group were integrated within the Company's existing businesses. The table below summarizes the preliminary purchase price allocation of net tangible and intangible assets acquired and liabilities assumed as of June 1, 2017 : (dollars in thousands) Cash and cash equivalents $ 30,562 Segregated cash 129,025 Securities owned, at fair value 3,417 Securities borrowed 258,321 Deposits from clearing organizations 52,596 Receivable from brokers 62,983 Receivable from customers 43,469 Fees receivable 36,232 Fixed assets, net 1,325 Intangible assets 10,270 Other assets 7,528 Securities sold, not yet purchased, at fair value (71 ) Securities loaned (286,359 ) Payable to brokers (74,284 ) Payable to customers (11,801 ) Commission management payable (82,718 ) Compensation payable (31,083 ) Notes payable and other debt (857 ) Fees payable (5,414 ) Accounts payable, accrued expenses and other liabilities (33,570 ) Total identifiable net assets acquired and liabilities assumed 109,571 Goodwill/(Bargain purchase gain) (11,609 ) Total estimated purchase price $ 97,962 The Company believes that all of the acquired receivables and contractual amounts receivable as reflected above in the allocation of the purchase price are recorded at fair value. See Note 22 for further information on legal matters relating to the acquisition. As of the acquisition date, the estimated fair value of the Company's intangible assets, as acquired through the acquisition, was $ 10.3 million . The allocation of the intangible assets is shown within the following table. Estimated intangible assets acquired Estimated average remaining useful lives (dollars in thousands) (in years) Intangible asset class Trade name $ 760 0.6 - 2.6 Intellectual property 1,790 5 Customer relationships 7,720 9 Total intangible assets $ 10,270 Amortization expense for the year ended December 31, 2017 is $1.4 million and is included in depreciation and amortization in the accompanying consolidated statements of operations. The estimated amortization expense related to these intangible assets in future periods is as follows: (dollars in thousands) 2018 $ 1,258 2019 1,239 2020 1,216 2021 1,216 2022 1,007 Thereafter 2,931 $ 8,867 Based on the June 1, 2017 estimated purchase price allocation, the fair value of the net identifiable assets acquired and liabilities assumed of $109.6 million exceeded the estimated purchase price of $98.0 million . As a result, the Company has recognized a bargain purchase gain of $11.6 million related to the acquisition. The bargain purchase gain is shown net of $4.7 million of associated tax in the accompanying consolidated statements of operations. In addition to the purchase price consideration, for the year ended December 31, 2017 , the Company has incurred acquisition related expenses of $ 6.0 million including financial advisory, legal and valuation services, which are included in professional, advisory and other fees in the consolidated statements of operations. Subsequent to the acquisition, certain of Convergex Group's businesses were integrated within the broker-dealer businesses of the Company and therefore they are included within their respective line items in the accompanying consolidated statements of operations from June 1, 2017 through December 31, 2017 . The following table provides unaudited supplemental pro forma financial information for the years ended December 31, 2017 and 2016, as if the acquisition were completed as of January 1, 2016. This unaudited supplemental pro forma information has been prepared for comparative purposes only and is not intended to be indicative of what the Company's financial results would have been had the acquisition been completed on January 1, 2016, nor does it purport to be indicative of any future results. Year Ended December 31, 2017 2016 (dollars in thousands, except per share data) (unaudited) Revenues $ 733,744 $ 681,655 Net income (loss) attributable to Cowen Inc. stockholders (84,671 ) (50,516 ) Net income (loss) per common share: Basic (a) $ (2.75 ) $ (1.68 ) Diluted (a) (2.75 ) (1.68 ) (a) Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016. In conjunction with the integration of the acquired businesses of Convergex Group, the Company evaluated the combined broker-dealer businesses and operations and incurred approximately $8.8 million of integration and restructuring costs which primarily related to exit and disposal costs, discontinuation of redundant technology services and severance costs. During the year ended December 31, 2017 , the Company continued to integrate the businesses acquired through Convergex Group and consolidated certain similar businesses. Low Country On April 22, 2016, Cowen Aviation Finance Holdings Inc. ("Cowen Aviation Finance") entered into a transaction whereby Cowen Aviation Finance acquired Low Country III, LLC, which is comprised of a portfolio of four specialized aircraft currently on lease in exchange for an immaterial upfront payment and a non-controlling equity interest in Cowen Aviation Finance. As part of the transaction Cowen Aviation Finance also acquired the associated debt financing and lease contracts for each aircraft. Separate from the transaction, Cowen Aviation Finance entered into services agreements with Tempus Applied Solutions, Inc., a related party through common directors, which, among other services, will provide marketing, maintenance, and lease administration services for Cowen Aviation Finance's current aircraft fleet. This acquisition was accounted for as an asset acquisition in accordance with US GAAP because, upon separation from the seller, the acquired assets do not meet the definition of a business. CRT business On May 6, 2016, the Company completed its previously announced acquisition of the credit products, credit research, special situations and emerging markets units from CRT Capital Group LLC (“CRT”). The acquisition was completed for a combination of cash of $6.3 million and contingent consideration payable annually based on future revenues exceeding specific targets. In the aggregate, the purchase price, assets acquired and liabilities assumed were not significant and the near term impact to the Company and its consolidated results of operations and cash flows is not expected to be significant. Following the acquisition, the businesses acquired from CRT are included in the broker-dealer segment. In accordance with the terms of the purchase agreement, the Company is required to pay to the sellers a portion of future revenue of the business exceeding specified targets over the period from the acquisition date through June 2018. The Company estimated the contingent consideration using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows. Changes in these estimates and assumptions could have a significant impact on the amount recognized. On the acquisition date, the undiscounted amount ranged from zero to $8.0 million . The acquisition was accounted for under the acquisition method of accounting in accordance with US GAAP. As such, the results of operations of the businesses acquired are included in the accompanying consolidated statements of operations since the date of the acquisition and the assets acquired, liabilities assumed and the resulting goodwill were recorded at their fair values within their respective line items on the accompanying consolidated statement of financial condition (see Note 12). The Company recognized approximately $0.4 million of acquisition-related costs, including legal, accounting, and valuation services. These costs are included in professional, advisory and other fees in the accompanying consolidated statements of operations. The Company also assumed contractual obligations, of up to $6 million , toward certain employees which vested over a 12 month period. These obligations are recorded as compensation expenses on a straight line basis. The results of operations of the businesses acquired from CRT for the period from May 6, 2016 through December 31, 2017 are integrated with the broker-dealer business and are included within their respective line items. Included in the accompanying consolidated statements of operations for the year ended December 31, 2017 are revenues of $33.2 million , respectively and net income of $9.3 million , respectively (excluding corporate allocated expenses) related to the businesses acquired from CRT. Divestiture On September 23, 2016, the Company and the portfolio managers of Ramius Alternative Solutions LLC ("RASL") completed the sale of their respective ownership interests in RASL, an investment advisor, and RASL was deconsolidated as of that date. RASL offered a range of customized private fund investment solutions with approximately $2.5 billion in client assets. In accordance with the terms of the agreement, the Company was only required to transfer an immaterial target working capital balance on the closing date. The net consideration received by the Company was approximately $17.3 million . Along with the target working capital transferred at closing, the Company also allocated a portion of goodwill associated with the investment management segment to the sale price which is shown net in other revenues in the accompanying consolidated statements of operations. As the Company will continue to offer its investment management platform to institutional and retail investors, the sale was not presented as discontinued operations. The overall impact on the consolidated financial position, results of operations and cash flows was not significant.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies a. Basis of Presentation These consolidated financial statements are prepared in accordance with US GAAP as promulgated by the Financial Accounting Standards Board ("FASB") through the Accounting Standards Codification as the source of authoritative accounting principles in the preparation of financial statements, and include the accounts of the Company, its operating and other subsidiaries, and entities in which the Company has a controlling financial interest or a general partner interest. All material intercompany transactions and balances have been eliminated on consolidation. Certain fund entities that are consolidated in these accompanying consolidated financial statements, as further discussed below, are not subject to the consolidation provisions with respect to their own controlled investments pursuant to their specialized accounting. The Company serves as the managing member/general partner and/or investment manager to affiliated fund entities which it sponsors and manages. Funds in which the Company has a controlling financial interest are consolidated with the Company pursuant to US GAAP as described below. Consequently, the Company's consolidated financial statements reflect the assets, liabilities, income and expenses of these funds on a gross basis. The ownership interests in these funds that are not owned by the Company are reflected as redeemable non-controlling interests in consolidated subsidiaries in the accompanying consolidated financial statements. The management fees and incentive income earned by the Company from these funds are eliminated in consolidation. Certain reclassifications have been made to prior period amounts in order to conform to current period presentation. b. Principles of consolidation The Company consolidates all entities that it controls through a majority voting interest or otherwise, including those funds in which the Company either directly or indirectly has a controlling financial interest. In addition, the Company consolidates all variable interest entities for which it is the primary beneficiary. In accordance with these standards, during the twelve months ended December 31, 2017 the Company consolidated seven funds for which it acts (or acted) as the general partner and investment manager. As of December 31, 2017 the Company consolidated the following funds: Ramius Enterprise LP (“Enterprise LP”), Ramius Merger Fund LLC (the "Merger Fund"), Cowen Private Investments LP ("Cowen Private"), Cowen Healthcare Investments Fund II LP ("Cowen Healthcare II"), Caerus Select Fund LP ("Caerus LP") (between May 1, 2016 through March 1, 2017 when the fund was liquidated), Ramius Archview Credit and Distressed Master Fund ("Archview Master Fund") (from December 31, 2015 through July 31, 2017 when the fund was liquidated) and Ramius Merger Arbitrage UCITS Fund ("UCITS Fund") (collectively the "Consolidated Funds"). The Company determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting operating entity ("VOE") or a variable interest entity ("VIE") under US GAAP. Voting Operating Entities — VOEs are entities in which (i) the total equity investment at risk is sufficient to enable the entity to finance its activities independently and (ii) the equity holders at risk have the obligation to absorb losses, the right to receive residual returns and the right to direct the activities of the entity that most significantly impact the entity's economic performance. Under US GAAP, the usual condition for a controlling financial interest in a VOE is ownership of a majority voting interest. Accordingly, the Company consolidates all VOEs in which it owns a majority of the entity's voting shares or units. Variable Interest Entities— VIEs are entities that lack one or more of the characteristics of a VOE. In accordance with US GAAP, an enterprise must consolidate all VIEs of which it is the primary beneficiary. Under the US GAAP consolidation model for VIEs, an enterprise that (1) has the power to direct the activities of a VIE that most significantly impacts the VIE's economic performance, and (2) has an obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE, is considered to be the primary beneficiary of the VIE and thus is required to consolidate it. The Company reconsiders whether it is the primary beneficiary of a VIE by performing a periodic qualitative and/or quantitative analysis of the VIE that includes a review of, among other things, its capital structure, contractual agreements between the Company and the VIE, the economic interests that create or absorb variability, related party relationships and the design of the VIE. As of December 31, 2017 and 2016 , the total net assets of the consolidated VIEs were $482.8 million and $461.6 million , respectively. The VIEs act as investment managers and/or investment companies that may be managed by the Company or the Company may have equity interest in those investment companies. The VIEs are financed through their operations and/or loan agreements with the Company. As of December 31, 2017 the Company holds variable interests in Ramius Enterprise Master Fund Ltd (“Enterprise Master”) and Ramius Merger Master Fund Ltd ("Merger Master") (collectively the “Unconsolidated Master Funds”) through the Consolidated Funds. Investment companies, which account for their investments under the specialized industry accounting guidance for investment companies prescribed under US GAAP, are not subject to the consolidation provisions for their investments. Therefore, the Company has not consolidated the Unconsolidated Master Funds. In the ordinary course of business, the Company also sponsors various other entities that it has determined to be VIEs. These VIEs are primarily funds and real estate entities for which the Company serves as the general partner, managing member and/or investment manager with decision-making rights. The Company does not consolidate the Unconsolidated Master Funds or real estate entities that are VIEs as it has concluded that it is not the primary beneficiary in each instance. Fund investors are entitled to all of their economics of these VIEs with the exception of the management fee and incentive income, if any, earned by the Company. The Company's involvement with funds and real estate entities that are unconsolidated VIEs is limited to providing investment management services in exchange for management fees and incentive income. Although the Company may advance amounts and pay certain expenses on behalf of the funds and real estate entities that it considers to be VIEs, it does not provide, nor is it required to provide, any type of substantive financial support to these entities outside of regular investment management services (see Note 6 for additional disclosures on VIEs). Equity Method Investments — For operating entities over which the Company exercises significant influence but which do not meet the requirements for consolidation as outlined above, the Company uses the equity method of accounting. The Company's investments in equity method investees are recorded in other investments in the accompanying consolidated statements of financial condition. The Company's share of earnings or losses from equity method investees is included in net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that the carrying amounts of such investments may not be recoverable. The difference between the carrying value of the equity method investment and its estimated fair value is recognized as an impairment charge when the loss in value is deemed other than temporary. Other — If the Company does not consolidate an entity, apply the equity method of accounting or account for an investment under the cost method, the Company accounts for such entities (primarily, all securities of such entity which are bought and held principally for the purpose of selling them in the near term as trading securities) in accordance with US GAAP, at fair value with unrealized gains (losses) resulting from changes in fair value reflected within net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. Retention of Specialized Accounting — The Consolidated Funds and certain other consolidated companies are investment companies and apply specialized industry accounting for investment companies. The Company has retained this specialized accounting for these funds pursuant to US GAAP. The Company reports its investments on the consolidated statements of financial condition at their estimated fair value, with unrealized gains (losses) resulting from changes in fair value reflected within net realized and unrealized gains (losses) on investments and other transactions. Accordingly, the accompanying consolidated financial statements reflect different accounting policies for investments depending on whether or not they are held through a consolidated investment company. In addition, the Company's broker-dealer subsidiaries , Cowen and Company, LLC ("Cowen and Company"), Cowen Execution, Westminster, Cowen Execution Ltd, ATM Execution LLC ("ATM Execution"), Cowen International Limited ("Cowen International Ltd"), Ramius UK Ltd. ("Ramius UK") and Cowen Prime Services LLC ("Cowen Prime") apply the specialized industry accounting for brokers and dealers in securities also prescribed under US GAAP. The Company also retains specialized accounting upon consolidation. c. Use of estimates The preparation of the accompanying consolidated financial statements in conformity with US GAAP requires the management of the Company to make estimates and assumptions that affect the fair value of securities and other investments, the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the accompanying consolidated financial statements, the accounting for goodwill and identifiable intangible assets and the reported amounts of revenues and expenses during the reporting period. Actual results could materially differ from those estimates. d. Cash and cash equivalents The Company considers investments in money market funds and other highly liquid investments with original maturities of three months or less which are deposited with a bank or prime broker to be cash equivalents. Cash and cash equivalents held at Consolidated Funds, although not legally restricted, are not available to fund the general liquidity needs of the Company. The Company may also be exposed to credit risk as a result of cash being held at several banks. e. Allowance for doubtful accounts The allowance for doubtful accounts is based on the Company’s assessment of the collectability of receivables related to securities transactions, prepaid research and other receivables. The Company considers factors such as historical experience, credit quality, age of balances and current economic conditions that may affect collectability in determining the allowance for doubtful accounts. Specifically for prepaid research, the Company reviews clients' historical, current and forecasted trading activity in determining the allowance for doubtful accounts. Expense related to the allowance for doubtful accounts as well as any recoveries of amounts previously charged is reflected in other expenses in the accompanying consolidated statements of operations. f. Valuation of investments and derivative contracts US GAAP establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1 measurements) and the lowest priority to unobservable inputs (level 3 measurements). The three levels of the fair value hierarchy are as follows: Level 1 Inputs that reflect unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date; Level 2 Inputs other than quoted prices that are observable for the asset or liability either directly or indirectly, including inputs in markets that are not considered to be active; and Level 3 Fair value is determined based on pricing inputs that are unobservable and includes situations where there is little, if any, market activity for the asset or liability. The determination of fair value for assets and liabilities in this category requires significant management judgment or estimation. Inputs are used in applying the various valuation techniques and broadly refer to the assumptions that market participants use to make valuation decisions, including assumptions about risk. Inputs may include price information, volatility statistics, specific and broad credit data, liquidity statistics, and other factors. A financial instrument's level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. However, the determination of what constitutes “observable” requires significant judgment by the Company. The Company considers observable data to be that market data which is readily available, regularly distributed or updated, reliable and verifiable, not proprietary, and provided by independent sources that are actively involved in the relevant market. The categorization of a financial instrument within the hierarchy is based upon the pricing transparency of the instrument and does not necessarily correspond to the Company's perceived risk of that instrument. The Company and its operating subsidiaries act as the manager for the Consolidated Funds. Both the Company and the Consolidated Funds hold certain investments which are valued by the Company, acting as the investment manager. The fair value of these investments is generally estimated based on proprietary models developed by the Company, which include discounted cash flow analysis, public market comparables, and other techniques and may be based, at least in part, on independently sourced market information. The material estimates and assumptions used in these models include the timing and expected amount of cash flows, the appropriateness of discount rates used, and, in some cases, the ability to execute, timing of, and estimated proceeds from expected financings. Significant judgment and estimation goes into the selection of an appropriate valuation methodology as well as the assumptions used in these models, and the timing and actual values realized with respect to investments could be materially different from values derived based on the use of those estimates. The valuation methodologies applied impact the reported value of the Company's investments and the investments held by the Consolidated Funds in the consolidated financial statements. Certain of the Company's investments are relatively illiquid or thinly traded and may not be immediately liquidated on demand if needed. Fair values assigned to these investments may differ significantly from the fair values that would have been used had a ready market for the investments existed and such differences could be material . The Company primarily uses the “market approach” to value its financial instruments measured at fair value. In determining an instrument's level within the hierarchy, the Company categorizes the Company's financial instruments into three categories: securities, derivative contracts and other investments. To the extent applicable, each of these categories can further be divided between those held long or sold short. The Company has the option to measure certain financial assets and financial liabilities at fair value with changes in fair value recognized in earnings each period. The election is made on an instrument by instrument basis at initial recognition of an asset or liability or upon an event that gives rise to a new basis of accounting for that instrument. The Company has elected the fair value option for certain of its investments held by its operating companies. This option has been elected because the Company believes that it is consistent with the manner in which the business is managed as well as the way that financial instruments in other parts of the business are recorded. Securities — Securities with values based on quoted market prices in active markets for identical assets are classified within level 1 of the fair value hierarchy. These securities include active listed equities, certain U.S. government and sovereign obligations, Exchange Traded Funds ("ETFs"), mutual funds and certain money market securities. The Company does not adjust the quoted price for such instruments, even in situations where the Company holds a large position and a sale could reasonably impact the quoted price. Certain positions for which trading activity may not be readily visible, consisting primarily of convertible debt, corporate debt and loans and restricted equities, are stated at fair value and classified within level 2 of the fair value hierarchy. The estimated fair values assigned by management are determined in good faith and are based on available information considering, trading activity, broker quotes, quotations provided by published pricing services, counterparties and other market participants, and pricing models using quoted inputs, and do not necessarily represent the amounts which might ultimately be realized. As level 2 investments include positions that are not always traded in active markets and/or are subject to transfer restrictions, valuations may be adjusted to reflect illiquidity and/or non-transferability. Derivative contracts — Derivative contracts can be exchange-traded or privately negotiated over-the-counter (“OTC”). Exchange-traded derivatives, such as futures contracts and exchange-traded option contracts, are typically classified within level 1 or level 2 of the fair value hierarchy depending on whether or not they are deemed to be actively traded. OTC derivatives, such as generic forwards, swaps and options, have inputs which can generally be corroborated by market data and are therefore classified within level 2. OTC derivatives, such as swaps and options where market data is not readily available or observable are classified as level 3. Other investments — Other investments consist primarily of portfolio funds, real estate investments and equity method investments, which are valued as follows : i. Portfolio funds— Portfolio funds (“Portfolio Funds”) include interests in funds and investment companies which may be managed by the Company or its affiliates. The Company follows US GAAP regarding fair value measurements and disclosures relating to investments in certain entities that calculate net asset value (“NAV”) per share (or its equivalent). The guidance permits, as a practical expedient, an entity holding investments in certain entities that either are investment companies as defined by the American Institute of Certified Public Accountants ("AICPA") Audit and Accounting Guide, Investment Companies, or have attributes similar to an investment company, and calculate net asset value per share or its equivalent for which the fair value is not readily determinable, to measure the fair value of such investments on the basis of that NAV per share, or its equivalent, without adjustment. In accordance with US GAAP, investments which are valued using NAV per share as a practical expedient are not categorized within the fair value hierarchy. ii. Real estate investments— Real estate debt and equity investments are valued at fair value. The fair value of real estate investments are estimated based on the price that would be received to sell an asset in an orderly transaction between marketplace participants at the measurement date. Real estate investments without a public market are valued based on assumptions and valuation techniques used by the Company. Such valuation techniques may include discounted cash flow analysis, prevailing market capitalization rates or earnings multiples applied to earnings from the investment, analysis of recent comparable sales transactions, actual sale negotiations and bona fide purchase offers received from third parties, consideration of the amount that currently would be required to replace the asset, as adjusted for obsolescence, as well as independent external appraisals. In general, the Company considers several valuation techniques when measuring the fair value of a real estate investment. However, in certain circumstances, a single valuation technique may be appropriate. Real estate investments are reviewed on a quarterly basis by the Company for significant changes at the property level or a significant change in the overall market which would impact the value of the real estate investment resulting in unrealized appreciation or depreciation. Real estate and capital markets are cyclical in nature. Property and investment values are affected by, among other things, the availability of capital, occupancy rates, rental rates and interest and inflation rates. In addition, the Company invests in real estate and real estate related investments for which no liquid market exists. The market prices for such investments may be volatile and may not be readily ascertainable. Amounts ultimately realized by the Company from investments sold may differ from the fair values presented, and the differences could be material. The Company's real estate investments are typically categorized as level 3 investments within the fair value hierarchy as management uses significant unobservable inputs in determining their estimated fair value. See Notes 6 and 7 for further information regarding the Company's investments, including equity method investments, and fair value measurements. g. Due from/due to related parties The Company may advance amounts and pay certain expenses on behalf of employees of the Company or other affiliates of the Company. These amounts settle in the ordinary course of business. Such amounts are included in due from and due to related parties, respectively, on the accompanying consolidated statements of financial condition. h. Receivable from and payable to brokers Receivable from and payable to brokers, includes cash held at clearing brokers, amounts receivable or payable for unsettled transactions, monies borrowed and proceeds from short sales equal to the fair value of securities sold, but not yet purchased. Pursuant to the Company's prime broker agreements, these balances are presented net (assets less liabilities) across balances with the same broker. i. Fees receivable Fees related to security transactions are reported net of an allowance for doubtful debts. An allowance for doubtful debts is taken on any commission receivables aged over 180 days. Corporate finance and syndicate receivables, include receivables relating to the Company’s investment banking and advisory engagements net of allowance for doubtful accounts. The Company records this allowance for doubtful accounts on these receivables on a specific identification basis. The future collectability of the receivables is reviewed on a monthly basis based on the following factors: aging (usually if outstanding greater than 90 days), known financial stability of the paying company as well as any other factors that might impact the collection of the outstanding fees. Management and incentive fees are earned as the managing member, general partner and/or investment manager to the Company's funds and are recognized on an accrual basis when earned. j. Securities borrowed and securities loaned Securities borrowed and securities loaned are carried at the amounts of cash collateral advanced or received on a gross basis. The related rebates are recorded in the accompanying consolidated statements of operations as interest and dividends income and interest and dividends expense. Securities borrowed transactions require the Company to deposit cash collateral with the lender. With respect to securities loaned, the Company receives cash collateral from the borrower. The initial collateral advanced or received approximates or is greater than the market value of securities borrowed or loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or returned, as necessary. Securities borrowed and loaned may also result in credit exposures for the Company in an event that the counterparties are unable to fulfill their contractual obligations. The Company minimizes its credit risk by continuously monitoring its credit exposure and collateral values by demanding additional or returning excess collateral in accordance with the netting provisions available in the master securities lending contracts in place with the counterparties. Fees and interest received or paid are recorded in interest and dividends income and interest and dividends expense, respectively, on an accrual basis in the accompanying consolidated statements of operations. In cases where the fair value basis of accounting is elected, any resulting change in fair value would be reported in net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. Accrued interest income and expense are recorded in receivable from brokers, dealers and clearing organizations and payable to brokers, dealers and clearing organizations, respectively, on an accrual basis in the accompanying consolidated statements of financial condition. At December 31, 2017 , the Company did not have any securities lending transactions for which fair value basis of accounting was elected. k. Fixed Assets Fixed assets are stated at cost less accumulated depreciation or amortization. Leasehold improvements are amortized on a straight-line basis over the lesser of their useful life or lease term. When the Company commits to a plan to abandon fixed assets or leasehold improvements before the end of its original useful life, the estimated depreciation or amortization period is revised to reflect the shortened useful life of the asset. Other fixed assets are depreciated on a straight-line basis over their estimated useful lives. Aircraft and related equipment, which are leased out under operating leases, are carried at cost less accumulated depreciation and are depreciated to estimated residual value using the straight-line method over the lease term or estimated useful life of the asset. Any assets received at the end of the lease are marked to the lower of cost or fair value with the adjustment recorded in other income. Asset Depreciable Lives Depreciation and/or Amortization Method Telephone and computer equipment 3-5 years Straight-line Computer software 3-8 years Straight-line Furniture and fixtures 5 years Straight-line Leasehold improvements 2-15 years Straight-line Capitalized lease asset 5 years Straight-line Aircraft and related equipment 10-20 years Straight-line Modifications to aircraft 4-10 years Straight-line l. Goodwill and intangible assets Goodwill represents the excess of the purchase price consideration of acquired companies over the estimated fair value assigned to the individual assets acquired and liabilities assumed. Goodwill is allocated to the Company's reporting units at the date the goodwill is initially recorded. Once goodwill has been allocated to the reporting units, it generally no longer retains its identification with a particular acquisition, but instead becomes identifiable with the reporting unit. As a result, all of the fair value of each reporting unit is available to support the value of goodwill allocated to the unit. In accordance with US GAAP, the Company tests goodwill for impairment on an annual basis, at December 31 st each year, or at an interim period if events or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Under US GAAP, the Company tests goodwill for impairment by assessing the qualitative factors including, macroeconomic environment, industry and market specific conditions, financial performance and events specific to the reporting unit to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying amount. Based on the results of the qualitative assessment the Company performs the two-step goodwill impairment test. The first step requires a comparison of the fair value of the reporting unit to its carrying value, including goodwill. If the fair value of the reporting unit exceeds its carrying value, the related goodwill is not considered impaired and no further analysis is required. If the carrying value of the reporting unit exceeds the fair value, there is an indication that the related goodwill might be impaired and the step two is performed to measure the amount of impairment, if any. The second step of the goodwill impairment test compares the implied fair value of the reporting unit's goodwill with its carrying amount to measure the amount of impairment, if any. The implied fair value of goodwill is determined in the same manner as the amount of goodwill recognized in a business combination. In other words, the estimated fair value of the reporting unit is allocated to all of its assets and liabilities (including any unrecognized intangible assets) as if the reporting unit had been acquired in a business combination and the fair value of the reporting unit was the purchase price paid. If the carrying amount of the reporting unit goodwill exceeds the implied fair value of that goodwill, an impairment is recognized in an amount equal to that excess. Goodwill impairment tests involve significant judgment in determining the estimates of future cash flows, discount rates, economic forecast and other assumptions which are then used in acceptable valuation techniques, such as the market approach (earning and/or transactions multiples) and/or income approach (discounted cash flow method). Changes in these estimates and assumptions could have a significant impact on the fair value and any resulting impairment of goodwill. See Note 12 for further discussion. Intangible assets with finite lives are amortized over their estimated average useful lives. The Company does not have any intangible assets deemed to have indefinite lives. Intangible assets are tested for potential impairment whenever events or changes in circumstances suggest that an asset or asset group's carrying value may not be fully recoverable. Similar to goodwill impairment test, an impairment loss, calculated as the difference between the estimated fair value and the carrying value of an asset or asset group, is recognized in the accompanying consolidated statements of operations if the sum of the estimated undiscounted cash flows relating to the asset or asset group is less than the corresponding carrying value. m. Debt Long-term debt is carried at the principal amount borrowed net of any unamortized discount/premium. The discount is accreted to interest expense using the effective interest method over the remaining life of the underlying debt obligations. Accrued but unpaid coupon interest is included in accounts payable, accrued expenses and other liabilities in the accompanying consolidated statements of financial condition. n. Deferred rent Deferred rent primarily consists of step rent, allowances from landlords and valuing the Company's lease properties acquired through business combinations in accordance with US GAAP. Step rent represents the difference between actual operating lease payments due and straight-line rent expense, which is recorded by the Company over the term of the lease, including the build-out period. This amount is recorded as deferred rent in the early years of the lease, when cash payments are generally lower than straight-line rent expense, and reduced in the later years of the lease when payments begin to exceed the straight-line expense. Landlord allowances are generally comprised of amounts received and/or promised to the Company by landlords and may be received in the form of cash or free rent. These allowances are part of the negotiated terms of the lease. The Company records a receivable from the landlord and a deferred rent liability when the allowances are earned. This deferred rent is amortized into in

Cash Collateral Pledged

Cash Collateral Pledged	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash Collateral Pledged	Cash Collateral Pledged As of December 31, 2017 and 2016 , the Company pledged cash collateral in the amount of $6.1 million and $7.8 million , respectively, which relates to letters of credit issued to the landlords of the Company's premises in New York City, Boston, Stamford and San Francisco. The Company also has pledged as collateral, $11.8 million , as of December 31, 2017 , and $5.5 million , as of December 31, 2016 , due between March 2018 and March 2021, for reinsurance agreements (See Note 23 ).

Segregated Cash

Segregated Cash	12 Months Ended
	Dec. 31, 2017
Segregated Cash [Abstract]
Restricted Assets Disclosure [Text Block]	Segregated Cash As of December 31, 2017 and 2016 , cash segregated in compliance with federal regulations and other restricted deposits of $116.3 million and $1.0 million , respectively, consisted of cash deposited in special bank accounts for the benefit of customers under SEC Rule 15c3-3 and cash held in accounts designated as Special Reserve Bank Accounts for Proprietary Accounts of Broker-Dealers ("PAB").

Investments of Operating Entiti

Investments of Operating Entities and Consolidated Funds	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments of Operating Entities and Consolidated Funds	Investments of Operating Entities and Consolidated Funds a. Operating Entities Securities owned, at fair value Securities owned, at fair value are held by the Company and are considered held for trading. Substantially all equity securities are pledged to the clearing brokers under terms which permit the clearing broker to sell or re-pledge the securities to others subject to certain limitations. As of December 31, 2017 and 2016 , securities owned, at fair value consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Common stocks (b) $ 640,065 $ 669,655 Preferred stock (b) 9,604 15,811 Warrants and rights (b) 9,604 8,335 U.S. Government securities (a) 2,807 3,780 Corporate bonds (d) 4,909 2,477 Convertible bonds (c) 282 250 Trade claims 5,950 562 Mutual funds (b) — 6 $ 673,221 $ 700,876 (a) As of December 31, 2017 , maturities ranged from February 2018 to June 2018 with an interest rate of 0% . As of December 31, 2016 , maturities ranged from February 2017 to December 2017 with an interest rate of 0% . (b) The Company has elected the fair value option for investments in securities of preferred and common stocks with a fair value of $6.0 million and $5.2 million , respectively, at December 31, 2017 and $7.0 million and $5.2 million , respectively, at December 31, 2016 . At December 31, 2017 , the Company elected the fair value option for investments in warrants and rights with a fair value of $2.4 million . At December 31, 2016 the Company elected the fair value option for investments in mutual funds with a fair value of $0.1 million . (c) As of December 31, 2017 , maturities ranged from February 2018 to March 2018 and interest rates ranged from 5% to 12% . As of December 31, 2016 , the maturity was March 2018 with an interest rate of 8% . (d) As of December 31, 2017 , maturities ranged from October 2018 to May 2040 and interest rates ranged from 0.00% to 10.75% . As of December 31, 2016 , maturities ranged from January 2017 to January 2036 and interest rates ranged from 6.25% to 13.00% . Receivable on and Payable for derivative contracts, at fair value The Company's direct involvement with derivative financial instruments includes total return swaps, futures, currency forwards, equity swaps, credit default swaps and options. The Company's derivatives trading activities exposes the Company to certain risks, such as price and interest rate fluctuations, volatility risk, credit risk, counterparty risk, foreign currency movements and changes in the liquidity of markets. Upon issuance of the Company's 3% cash convertible senior notes due 2022 in December 2017 ("2022 Convertible Notes") (See Note 23 ), the Company recognized the embedded cash conversion option at fair value of $23.4 million which is valued as of December 31, 2017 at $22.1 million and is included in payable for derivative contracts in the accompanying consolidated statement of financial condition. Upon issuance of the Company's 3% cash convertible senior notes due 2019 in March 2014 (the "2019 Convertible Notes") (See Note 23 ), the Company recognized the embedded cash conversion option at fair value of $35.7 million which is valued as of December 31, 2017 at $0.3 million and is included in payable for derivative contracts in the accompanying consolidated statement of financial condition. Also, on the date of issuance of the 2019 Convertible Notes, the Company entered into a separate cash convertible note economic hedge transaction (the "Hedge Transaction") with a counterparty (the “Option Counterparty”) whereby, the Company purchased a cash settled option contract with terms identical to the conversion option embedded in the 2019 Convertible Notes and simultaneously sold an equity settled warrant with a higher strike price. The Hedge Transaction is expected to reduce the Company’s exposure to potential cash payments in excess of the principal amount of converted notes that the Company may be required to make upon conversion of the 2019 Convertible Notes. The Company paid a premium of $35.7 million for the option under the Hedge Transaction and received a premium of $15.2 million for the equity settled warrant transaction, for a net cost of $20.5 million . The Hedge Transaction is valued at $1.5 million as of December 31, 2017 and is included in receivable on derivative contracts in the accompanying consolidated statement of financial condition. Aside from the initial premium paid, the Company will not be required to make any cash payments under the Hedge Transaction and could be entitled to receive an amount of cash from the Option Counterparty generally equal to the amount by which the market price per share of common stock exceeds the strike price of the Hedge Transaction during the relevant valuation period. The warrants cover 7,012,196 shares of the Company's Class A common stock and have an initial exercise price of $28.72 per share ( share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016 ). The warrants expire over a period of 80 trading days beginning on November 14, 2018. The warrant transaction could have a dilutive effect to the extent that the market value per share of the Company’s Class A common stock exceeds the applicable strike price of the warrants. The Company's long and short exposure to derivatives is as follows: Receivable on derivative contracts As of December 31, 2017 2016 Number of contracts / Notional Value Fair value Number of contracts / Notional Value Fair value (dollars in thousands) Futures $ 3,819 $ 58 $ 12,421 $ 104 Currency forwards $ 233 5 $ 80,608 592 Swaps $ 164,664 10,942 $ 46,462 468 Options other (a) 283,112 58,172 256,097 21,539 Foreign currency options $ — — $ 57,051 198 $ 69,177 $ 22,901 (a) Includes index, equity, commodity future and cash conversion options. Payable for derivative contracts As of December 31, 2017 2016 Number of contracts / Notional Value Fair value Number of contracts / Notional Value Fair value (dollars in thousands) Futures $ 16,796 $ 242 $ 38,345 $ 642 Currency forwards $ 62,439 874 $ — — Swaps $ 11,595 71 $ 9,533 181 Options other (a) 57,043 41,563 23,726 19,939 $ 42,750 $ 20,762 (a) Includes index, equity, commodity future and cash conversion options. The following tables present the gross and net derivative positions and the related offsetting amount, as of December 31, 2017 and 2016 . This table does not include the impact of over collateralization. Gross amounts not offset in the Consolidated Statement of Financial Condition Gross amounts recognized Gross amounts offset on the Consolidated Statements of Financial Condition (a) Net amounts included on the Consolidated Statements of Financial Condition Financial instruments Cash Collateral pledged (b) Net amounts (dollars in thousands) As of December 31, 2017 Receivable on derivative contracts, at fair value $ 69,177 $ — $ 69,177 $ — $ 10,948 $ 58,229 Payable for derivative contracts, at fair value 42,750 — 42,750 — 1,031 41,719 As of December 31, 2016 Receivable on derivative contracts, at fair value 22,901 — 22,901 — 1,382 21,519 Payable for derivative contracts, at fair value 20,762 — 20,762 — 181 20,581 (a) Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred. (b) Includes the amount of collateral held or posted. The realized and unrealized gains/(losses) related to derivatives trading activities were $3.9 million , $(11.2) million and $(5.6) million for the years ended December 31, 2017 , 2016 , and 2015, respectively, and are included in other income in the accompanying consolidated statements of operations. Pursuant to the various derivatives transactions discussed above, except for the cash convertible note hedge (see Note 23 ) and exchange traded derivatives, the Company is required to post/receive collateral. As of December 31, 2017 and 2016 , collateral consisting of $13.5 million and $17.1 million of cash, respectively, is included in receivable from brokers, dealers and clearing organizations and payable to brokers, dealers and clearing organizations on the accompanying consolidated statements of financial condition. As of December 31, 2017 and 2016 all derivative contracts were with multiple major financial institutions. Other investments As of December 31, 2017 and 2016 , other investments included the following: As of December 31, 2017 2016 (dollars in thousands) Portfolio Funds, at fair value (1) $ 100,148 $ 120,023 Equity method investments (2) 41,099 36,991 Lehman claims, at fair value 301 265 $ 141,548 $ 157,279 (1) Portfolio Funds, at fair value The Portfolio Funds, at fair value as of December 31, 2017 and 2016 , included the following: As of December 31, 2017 2016 (dollars in thousands) Starboard Value and Opportunity Fund LP (c)(*) $ 32,079 $ 27,424 Formation8 Partners Fund I, L.P. (f) 28,243 22,234 RCG Longview Debt Fund V, L.P. (i)(*) 8,892 16,187 HealthCare Royalty Partners LP (a)(*) 3,452 7,147 Eclipse Ventures Fund I, L.P. (g) 3,428 1,790 Lagunita Biosciences, LLC (n) 2,400 1,698 RCG LPP2 PNW5 Co-Invest, L.P. (j)(*) 3,493 3,152 Starboard Leaders Fund LP (e)(*) 1,276 1,231 HealthCare Royalty Partners II LP (a)(*) 873 2,091 Quadratic Fund LLC (k) (*) 906 6,729 RCGL 12E13th LLC (i)(*) 237 348 RCG Park Liberty GP Member LLC (i) (*) 750 598 RCG Longview Debt Fund VI, LP (i) (*) 1,022 — Green Energy Metals Fund, LP (h) — 6,241 Starboard Partners Fund LP (d)(*) — 5,067 Orchard Square Partners Credit Fund LP (b) — 4,327 Other private investment (l)(*) 10,133 8,548 Other affiliated funds (m)(*) 2,964 5,211 $ 100,148 $ 120,023 * These portfolio funds are affiliates of the Company. The Company has no unfunded commitments regarding the portfolio funds held by the Company except as noted in Note 22 . (a) HealthCare Royalty Partners, L.P. and HealthCare Royalty Partners II, L.P. are private equity funds and therefore distributions will be made when cash flows are received from the underlying investments, typically on a quarterly basis. (b) Orchard Square Partners Credit Fund LP had a quarterly redemption policy with a 60 day notice period and a 4% penalty on redemptions of investments of less than a year in duration. (c) Starboard Value and Opportunity Fund LP permits quarterly withdrawals upon 90 days' notice. (d) Starboard Partners Fund LP permitted redemptions on a semi-annual basis on 180 days' prior written notice subsequent to an initial two year lock up. (e) Starboard Leaders Fund LP does not permit withdrawals, but instead allows terminations with respect to capital commitments upon 30 days' prior written notice at any time following the first anniversary of an investors' initial capital contribution. (f) Formation8 Partners Fund I, L.P. is a private equity fund which invests in early stage and growth transformational information and energy technology companies. Distributions will be made when the underlying investments are liquidated. (g) Eclipse Ventures Fund I, L.P. is a private equity fund which invests in early stage and growth hardware companies. Distributions will be made when the underlying investments are liquidated. (h) The Green Energy Metals Fund, LP invested the vast majority of its capital in physical off-exchange traded minor metals that are crucial to the production and sustainability of clean energy, emerging technology and energy efficiency. The Company was invested in a managed account specifically targeting cobalt. The Green Energy Metals Fund, LP is a private equity structure and therefore distributions were made when the underlying investments were liquidated. (i) RCGL 12E13th LLC, RCG Longview Debt Fund V, L.P., RCG Park Liberty GP Member LLC, and RCG Longview Debt Fund VI, LP are real estate private equity structures and therefore distributions will be made when the underlying investments are liquidated. (j) RCG LPP2 PNW5 Co-Invest, L.P. is a single purpose entity formed to participate in a joint venture which acquired five multi-unit residential rental properties located in the Pacific Northwest. RCG LPP2 PNW5 Co-Invest, L.P. is a private equity structure and therefore distributions will be made when the underlying investments are liquidated. (k) Quadratic Fund LLC permits redemptions 30 days prior written notice. (l) Other private investment represents the Company's closed end investment in a portfolio fund that invests in a wireless broadband communication provider in Italy. (m) The majority of these funds are affiliates of the Company or are managed by the Company and the investors can redeem from these funds as investments are liquidated. (n) Lagunita Biosciences, LLC, a healthcare investment company that creates and grows early stage companies to commercialize impactful translational science that addresses significant clinical needs, is a private equity structure and therefore distributions will be made when the underlying investments are liquidated. (2) Equity method investments Equity method investments include investments held by the Company in several operating companies whose operations primarily include the day to day management of a number of real estate funds, including the portfolio management and administrative services related to the acquisition, disposition, and active monitoring of the real estate funds' underlying debt and equity investments. The Company's ownership interests in these equity method investments range from 20% to 57% . The Company holds a majority of the outstanding ownership interest (i.e., more than 50%) in RCG Longview Partners II, LLC and 43% in Surf House Ocean Views Holdings, LLC (which is a joint venture in a real estate development project). The operating agreement that governs the management of day-to-day operations and affairs of these entities stipulates that certain decisions require support and approval from other members in addition to the support and approval of the Company. As a result, all operating decisions made in these entities requires the support of both the Company and an affirmative vote of a majority of the other managing members who are not affiliates of the Company. As the Company does not possess control over any of these entities, the presumption of consolidation has been overcome pursuant to current accounting standards and the Company accounts for these investments under the equity method of accounting. Also included in equity method investments are the investments in (a) HealthCare Royalty Partners General Partners and (b) Starboard Value (and certain related parties) which serves as an operating company whose operations primarily include the day to day management (including portfolio management) of several activist private funds and related managed accounts. As part of its equity method investment in operating companies, the Company incurs certain expenses on behalf of its equity method investees. These expenses reflect direct and indirect costs associated with the respective business and are included in their respective line items in the accompanying consolidated statements of operations. For the years ended December 31, 2017 , 2016 , and 2015, the Company incurred $7.1 million , $8.5 million and $14.1 million of these costs, respectively. The Company recorded no impairment charges in relation to its equity method investments for the years ended December 31, 2017 , 2016 and 2015. The following table summarizes equity method investments held by the Company: As of December 31, 2017 2016 (dollars in thousands) Surf House Ocean Views Holdings, LLC $ 14,179 $ 13,522 Starboard Value LP 13,202 12,501 RCG Longview Debt Fund V Partners, LLC 9,284 7,256 RCG Longview Management, LLC 1,149 656 HealthCare Royalty GP, LLC 281 583 HealthCare Royalty GP II, LLC 148 354 RCG Longview Debt Fund IV Management, LLC 331 331 HealthCare Royalty GP III, LLC 764 208 RCG Kennedy House, LLC 154 183 RCG Longview Equity Management, LLC 114 114 RCG LPP II GP, LLC 487 — RCG Park Liberty GP Member Manager, LLC 428 141 Other 578 1,142 $ 41,099 $ 36,991 For the period ended December 31, 2017 , three equity method investments have met the significance criteria as defined under Regulation S-X Rule 4-08(g) of the SEC guidance. As such, the Company is presenting the following summarized financial information for the significant investees for the years ended December 31, 2017 , 2016, and 2015, and such information is as follows: As of December 31, 2017 2016 (dollars in thousands) Assets Cash $ 6,046 $ 5,766 Performance & management fee receivable 110,064 48,145 Investments in Portfolio Funds, at fair value 11,251 7,493 Other assets 1,060 1,122 Liabilities 74,256 21,250 Equity $ 54,165 $ 41,276 Year Ended December 31, 2017 2016 2015 (dollars in thousands) Revenues $ 132,862 $ 87,371 $ 35,268 Expenses (32,354 ) (34,490 ) (20,658 ) Net realized and unrealized gains (losses) 9,264 9,383 4,259 Net Income $ 109,772 $ 62,264 $ 18,869 For the period ended December 31, 2017 , equity method investments held by the Company in aggregate have met the significance criteria as defined under SEC guidance. As such, the Company is required to present summarized financial information for these significant investees for the years ended December 31, 2017 , 2016 and 2015, and such information is as follows: As of December 31, 2017 2016 (dollars in thousands) Assets $ 155,936 $ 88,965 Liabilities 74,316 22,504 Equity $ 81,620 $ 66,461 Year Ended December 31, 2017 2016 2015 (dollars in thousands) Revenues $ 137,052 $ 90,337 $ 38,571 Expenses (32,354 ) (34,490 ) (20,658 ) Net realized and unrealized gains (losses) 10,149 (6,305 ) 9,715 Net Income $ 114,847 $ 49,542 $ 27,628 As of December 31, 2017 and 2016 , the Company's share of losses in its equity method investment in RCG Longview Partners II, LLC has exceeded the carrying amount recorded in this investee. These amounts are included in accounts payable, accrued expenses and other liabilities in the accompanying consolidated statements of financial condition. RCG Longview Partners II, LLC, as general partner to a real estate fund, has reversed previously recorded incentive income allocations and has recorded a current clawback obligation to the limited partners in the fund. This obligation is due to a change in unrealized value of the fund on which there have previously been distributed carried interest realizations; however, the settlement of a potential obligation is not due until the end of the life of the respective fund. As the Company is obligated to return previous distributions it received from RCG Longview Partners II, LLC, it has continued to record its share of gains/losses in the investee including reflecting its share of the clawback obligation in the amount of $6.2 million . The Company's income (loss) from equity method investments was $21.3 million , $14.4 million , and $3.4 million for the years ended December 31, 2017 , 2016 , and 2015 respectively, and is included in net gains (losses) on securities, derivatives and other investments on the accompanying consolidated statements of operations. Securities sold, not yet purchased, at fair value Securities sold, not yet purchased, at fair value represent obligations of the Company to deliver a specified security at a contracted price and, thereby, create a liability to purchase that security at prevailing prices. The Company's liability for securities to be delivered is measured at their fair value as of the date of the consolidated financial statements. However, these transactions result in off-balance sheet risk, as the Company's ultimate cost to satisfy the delivery of securities sold, not yet purchased, at fair value may exceed the amount reflected in the accompanying consolidated statements of financial condition. Substantially all equity securities and options are pledged to the clearing broker under terms which permit the clearing broker to sell or re-pledge the securities to others subject to certain limitations. As of December 31, 2017 and 2016 , securities sold, not yet purchased, at fair value consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Common stocks $ 342,328 $ 263,460 Corporate bonds (a) 122 2,591 Preferred stock 77 — Warrants and rights — 39 $ 342,527 $ 266,090 (a) As of December 31, 2017 , the maturities ranged from July 2025 to January 2036 with interest rates ranged from 3.78% to 5.55% . As of December 31, 2016 , the maturities ranged from April 2021 to January 2036 with interest rates ranged from 5.50% to 6.25% . Securities lending and borrowing transactions The following tables present the contractual gross and net securities borrowing and lending agreements and the related offsetting amount, as of December 31, 2017 . Gross amounts not offset on the Consolidated Statements of Financial Condition Gross amounts recognized Gross amounts offset on the Consolidated Statements of Financial Condition (a) Net amounts included on the Consolidated Statements of Financial Condition Additional Amounts Available Financial instruments Cash Collateral pledged (b) Net amounts (dollars in thousands) As of December 31, 2017 Securities borrowed $ 443,148 $ — $ 443,148 $ — $ 414,778 $ — $ 28,370 Securities loaned 456,831 — 456,831 — 439,228 — 17,603 (a) Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred. (b) Includes the amount of cash collateral held/posted. The following tables present gross obligations for securities loaned transactions by remaining contractual maturity and class of collateral pledged as of December 31, 2017 : Open and Overnight Up to 30 days 31 - 90 days Greater than 90 days Total (dollars in thousands) As of December 31, 2017 Equities $ 456,831 $ — $ — $ — $ 456,831 Variable Interest Entities The total assets and liabilities of the variable interest entities for which the Company has concluded that it holds a variable interest, but for which it is not the primary beneficiary, are $5.2 billion and $445.6 million as of December 31, 2017 and $5.3 billion and $997.3 million as of December 31, 2016 , respectively. In addition, the maximum exposure relating to these variable interest entities as of December 31, 2017 was $471.3 million , and as of December 31, 2016 was $508.1 million , all of which is included in other investments, at fair value in the accompanying consolidated statements of financial condition. The exposure to loss primarily relates to the Consolidated Feeder Funds' investment in their Unconsolidated Master Funds and the Company's investment in unconsolidated investment companies. b. Consolidated Funds Securities owned, at fair value As of December 31, 2017 and 2016 , securities owned, at fair value, held by the Consolidated Funds consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Preferred stock $ 50,445 $ 37,343 Common stocks 77,702 28,474 U.S. Government securities (a) 34,201 6,994 Corporate bonds (b) — 4,214 Term Loan — 2,209 Warrants and rights 3,568 3 $ 165,916 $ 79,237 (a) As of December 31, 2017 , maturities ranged from January 2018 2017 to April 2022 and interest rates ranged from 0% to 5.75% . As of December 31, 2016 , the maturity was March 2017 with an interest rate of 0% . (b) As of December 31, 2016 , maturities ranged from October 2017 to June 2038 and interest rates ranged from 0% and 14.37% . Securities sold, not yet purchased, at fair value As of December 31, 2017 , there were no securities sold, not yet purchased, at fair value. As of December 31, 2016 , securities sold, not yet purchased, at fair value, held by the Consolidated Funds consisted of the following: As of December 31, 2016 (dollars in thousands) Corporate bonds (a) $ 672 Common stocks 211 $ 883 (a) As of December 31, 2016 , maturities ranged from September 2019 to September 2023 and interest rates ranged from 4.38% to 9.25% . Receivable on derivative contracts As of December 31, 2017 and 2016 , receivable on derivative contracts, at fair value, held by the Consolidated Funds are comprised of: As of December 31, 2017 2016 (dollars in thousands) Currency forwards $ 524 $ 18 Equity swaps 1,754 731 Options 242 144 $ 2,520 $ 893 Payable for derivative contracts As of December 31, 2017 and 2016 , payable for derivative contracts, at fair value, held by the Consolidated Funds are comprised of: As of December 31, 2017 2016 (dollars in thousands) Currency forwards $ 11 $ 10 Equity swaps 7,042 495 Options 77 67 $ 7,130 $ 572 Other investments, at fair value Investments in Portfolio Funds, at fair value As of December 31, 2017 and 2016 , investments in Portfolio Funds, at fair value, included the following: As of December 31, 2017 2016 (dollars in thousands) Investments of Enterprise LP $ 87,221 $ 114,159 Investments of Merger Fund 286,890 281,572 Investments of Caerus LP — 5,734 $ 374,111 $ 401,465 Consolidated portfolio fund investments of Enterprise LP Enterprise LP operates under a “master-feeder” structure, whereby Enterprise Master's shareholders are Enterprise LP and RCG II Intermediate Fund, L.P. The consolidated investments in Portfolio Funds include Enterprise LP's investment of $87.2 million and $114.2 million in Enterprise Master as of December 31, 2017 and 2016 , respectively. On May 12, 2010, the Company announced its intention to close Enterprise Master. Prior to this announcement, strategies utilized by Enterprise Master included merger arbitrage and activist investing, investments in distressed securities, convertible hedging, capital structure arbitrage, equity market neutral, investments in private placements of convertible securities, proprietary mortgages, structured credit investments, investments in mortgage backed securities and other structured finance products, investments in real estate and real property interests, structured private placements and other relative value strategies. Enterprise Master had broad investment powers and maximum flexibility in seeking to achieve its investment objective. Enterprise Master was permitted to invest in equity securities, debt instruments, options, futures, swaps, credit default swaps and other derivatives. As Enterprise Master winds down its positions, it will return capital to its investors. There are no unfunded commitments at Enterprise LP. Consolidated portfolio fund investments of Merger Fund The Merger Fund operates under a “master-feeder” structure, whereby Ramius Merger Master Ltd.'s ("Merger Master") shareholders are Merger Fund and Ramius Merger Fund Ltd. The consolidated investments in Portfolio Funds include Merger Fund's investment of $286.9 million and $281.6 million in Merger Master as of December 31, 2017 and 2016 , respectively. The Merger Master’s investment objective is to achieve consistent absolute returns while emphasizing the preservation of investor capital. The Merger Master seeks to achieve these objectives by taking a fundamental, research-driven approach to investing, primarily in the securities of issuers engaged in, or subject to, announced (or unannounced but otherwise anticipated) extraordinary corporate transactions, which may include, but are not limited to, mergers, acquisitions, leveraged buyouts, tender offers, hostile takeover bids, sale processes, exchange offers, and recapitalizations. Merger Master invests in the securities of one or more issuers engaged in or subject to such extraordinary corporate transactions. Merger Master typically seeks to derive a profit by realizing the price differential, or “spread,” between the market price of securities purchased or sold short and the market price or value of securities realized in connection with the completion or termination of the extraordinary corporate transaction, or in connection with the adjustment of market prices in anticipation thereof, while seeking to minimize the market risk associated with the aforementioned investment activities. Merger Master will, depending on market conditions, generally focus the majority of its investment program on announced transactions. If the investment manager of Merger Master considers it necessary, it may either alone or as part of a group, also initiate shareholder actions seeking to maximize value. Such shareholder actions may include, but are not limited to, re-orienting management’s focus or initiating the sale of the company (or one or more of its divisions) to a third party. There are no unfunded commitments at Merger Fund. Consolidated portfolio fund investments of Caerus LP Prior to Caerus LP being liquidated on March 1, 2017, it operated under a “master-feeder” structure, whereby Caerus Select Master Fund Ltd.'s ("Caerus Master") shareholder was Caerus LP. The consolidated investments in Portfolio Funds included Caerus LP's investment of $5.7 million in Caerus Master as of December 31, 2016 . Caerus Master’s investment objective was to achieve superior risk-adjusted rates of return that bear little correlation to the overall market. Caerus Master sought to achieve this objective by utilizing a long/short investment strategy, investing primarily in equities and options on equities that trade on major global market exchanges. Caerus Master focused on investments in the global consumer sector, including, but not limited to, securities in sub-sectors such as retail, apparel and footwear, restaurants, gaming and lodging, consumer products, food and beverage, consumer technology, media, transportation and homebuilding and building materials. Indirect Concentration of the Underlying Investments Held by Consolidated Funds From time to time, either directly or indirectly through its investments in the Consolidated Funds, the Company may maintain exposure to a particular issue or issuer (both long and/or short) which may account for 5% or more of the Company's equity. Based on information that is available to the Company as of December 31, 2017 and 2016 , the Company assessed whether or not its interests in an issuer for which the Company's pro-rata share exceeds 5% of the Company's equity. There was one indirect concentration that exceeded 5% of the Company's equity as of December 31, 2017 and none at December 31, 2016 . Through its investments in a Consolidated Fund and combined with direct Company investments, the Company maintained exposure to a particular investment which accounted for 5% or more of the Company's equity. Investment's percentage of the Company's equity at December 31, 2017 Issuer Security Type Country Industry Percentage of Equity Market Value (dollars in thousands) Linkem Equity Italy Wireless Broadband 7.52 % $ 56,271 Underlying Investments of Unconsolidated Funds Held by Consolidated Funds Enterprise Master and Merger Master Enterprise LP's investment in Enterprise Master represents Enterprise LP's proportionate share of Enterprise Master's net assets; as a result, the investment balances of Enterprise Master reflected below may exceed the net investment which Enterprise LP has recorded. Merger Fund's investment in Merger Master represents Merger Fund's proportionate share of Merger Master's net assets; as a result, the investment balances of Merger Master reflected below may exceed the net investment which Merger Fund has recorded. The following tables present summarized investment information for the underlying investments and derivatives held by Enterprise Master and Merger Master as of December 31, 2017 and 2016 : Securities owned by Enterprise Master, at fair value As of December 31, 2017 2016 (dollars in thousands) Preferred stock $ — $ 1,581 Common stock 608 835 $ 608 $ 2,416 Portfolio Funds, owned by Enterprise Master, at fair value As of December 31, 2017 2016 Strategy (dollars in thousands) RCG Special Opportunities Fund, Ltd* Multi-Strategy $ 97,345 $ 101,832 RCG Longview Equity Fund, LP* Real Estate 1,266 4,744 RCG Longview Debt Fund IV, LP* Real Estate 99 1,637 RCG Longview II, LP* Real Estate 229 836 RCG Renergys, LLC* Energy — 1 Other Private Investments Various 937 8,682 Other Real Estate Investments * Real Estate — 295 $ 99,876 $ 118,027 * Affiliates of the Company. Merger Master As of December 31, 2017 , Merger Master held common stock, securities owned, of $483.2 million and common stock, sold not yet purchased, of $171.2 million . As of December 31, 2016 , Merger Master held common stock, securities owned, of $835.7 million and common stock, sold not yet purchased, of $395.5 million , respectively. Receivable on derivative contracts, at fair value, owned by Merger Master As of December 31, 2017 2016 Description (dollars in thousands) Options $ 108,063 $ 4,264 Equit

Fair Value Measurements for Ope

Fair Value Measurements for Operating Entities and Consolidated Funds	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements for Operating Entities and Consolidated Funds	Fair Value Measurements for Operating Entities and Consolidated Funds The following table presents the assets and liabilities that are measured at fair value on a recurring basis on the accompanying consolidated statements of financial condition by caption and by level within the valuation hierarchy as of December 31, 2017 and 2016 : Assets at Fair Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities owned US Government securities $ 2,807 $ — $ — $ 2,807 Preferred stock 571 918 8,115 9,604 Common stocks 627,011 5,484 7,570 640,065 Convertible bonds — — 282 282 Corporate bonds — 4,909 — 4,909 Trade claims — — 5,950 5,950 Warrants and rights 7,087 — 2,517 9,604 Receivable on derivative contracts, at fair value Futures 58 — — 58 Currency forwards — 5 — 5 Swaps — 10,942 — 10,942 Options 56,717 — 1,455 58,172 Other investments Lehman claim — — 301 301 Consolidated Funds Securities owned US Government securities 30,552 3,649 — 34,201 Preferred stock — — 50,445 50,445 Common stocks 77,652 — 50 77,702 Warrants and rights — — 3,568 3,568 Receivable on derivative contracts, at fair value Currency forwards — 524 — 524 Equity swaps — 1,754 — 1,754 Options 242 — — 242 $ 802,697 $ 28,185 $ 80,253 $ 911,135 Percentage of total assets measured at fair value on a recurring basis 88.1 % 3.1 % 8.8 % Portfolio funds measured at net asset value (a) 100,148 Consolidated funds' portfolio funds measured at net asset value (a) 374,111 Equity method investments 41,099 Total investments $ 1,426,493 Liabilities at Fair Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities sold, not yet purchased Common stocks $ 342,328 $ — $ — $ 342,328 Corporate bonds — 122 — 122 Preferred stock 77 — — 77 Warrants and rights — — — — Payable for derivative contracts, at fair value Futures 242 — — 242 Currency forwards — 874 — 874 Swaps — 71 — 71 Options 19,162 — 22,401 41,563 Accounts payable, accrued expenses and other liabilities Contingent consideration liability (b) — — 3,440 3,440 Consolidated Funds Payable for derivative contracts, at fair value Currency forwards — 11 — 11 Options 77 — — 77 Equity swaps — 7,042 — 7,042 $ 361,886 $ 8,120 $ 25,841 $ 395,847 Percentage of total liabilities measured at fair value 91.4 % 2.1 % 6.5 % (a) In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition. (b) In accordance with the terms of the purchase agreements for acquisitions that closed during the third and fourth quarter of 2015 and the second quarter of 2016, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, December 2020, and June 2018, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2017 can range from $0.1 million to $15.0 million . Assets at Fair Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities owned US Government securities $ 3,780 $ — $ — $ 3,780 Preferred stock — — 15,811 15,811 Common stocks 658,179 1,355 10,121 669,655 Convertible bonds — — 250 250 Corporate bonds — 2,477 — 2,477 Trade claims — — 562 562 Warrants and rights 4,616 — 3,719 8,335 Mutual funds 6 — — 6 Receivable on derivative contracts, at fair value Futures 104 — — 104 Currency forwards — 592 — 592 Swaps — 468 — 468 Options 6,662 322 14,753 21,737 Other investments Lehman claim — — 265 265 Consolidated Funds Securities owned US Government securities 6,994 — — 6,994 Preferred stock — 415 36,928 37,343 Common stocks 19,467 8,712 295 28,474 Corporate bonds — 4,214 — 4,214 Warrants and rights — — 3 3 Term loan — 1,552 657 2,209 Receivable on derivative contracts, at fair value Currency forwards — 18 — 18 Equity swaps — 731 — 731 Options 132 12 — 144 $ 699,940 $ 20,868 $ 83,364 $ 804,172 Percentage of total assets measured at fair value on a recurring basis 87.0 % 2.6 % 10.4 % Portfolio funds measured at net asset value (a) 120,023 Consolidated funds' portfolio funds measured at net asset value (a) 401,465 Equity method investments 36,991 Total investments $ 1,362,651 Liabilities at Fair Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities sold, not yet purchased Common stocks $ 263,460 $ — $ — $ 263,460 Corporate bonds — 2,591 — 2,591 Warrants and rights 39 — — 39 Payable for derivative contracts, at fair value Futures 642 — — 642 Swaps — 181 — 181 Options 5,186 — 14,753 19,939 Accounts payable, accrued expenses and other liabilities Contingent consideration liability (b) — — 5,997 5,997 Consolidated Funds Securities sold, not yet purchased Common stocks 211 — — 211 Corporate bonds — 672 — 672 Payable for derivative contracts, at fair value Currency forwards — 10 — 10 Options 67 — — 67 Equity swaps — 495 — 495 $ 269,605 $ 3,949 $ 20,750 $ 294,304 Percentage of total liabilities measured at fair value 91.6 % 1.3 % 7.1 % (a) In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition. (b) In accordance with the terms of the purchase agreements for acquisitions that closed during 2012 and the third and fourth quarter of 2015, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, and December 2020, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2016 can range from $0.1 million to $15.1 million . The following table includes a roll forward of the amounts for the year ended December 31, 2017 and 2016 for financial instruments classified within level 3. The classification of a financial instrument within level 3 is based upon the significance of the unobservable inputs to the overall fair value measurement. Year Ended December 31, 2017 Balance at December 31, 2016 Transfers in Transfers out Purchases/(covers) (Sales)/shorts Realized and Unrealized gains/losses Balance at December 31, 2017 Change in unrealized gains/losses relating to instruments still held (1) (dollars in thousands) Operating Entities Preferred stock $ 15,811 $ — $ (25,098 ) (a) (f) $ 25,785 $ (2,956 ) $ (5,427 ) $ 8,115 $ 486 Common stocks 10,121 — — 2,670 (2,688 ) (2,533 ) 7,570 (412 ) Convertible bonds 250 — — 282 — (250 ) 282 — Options, asset 14,753 — — — — (13,298 ) 1,455 (13,298 ) Options, liability 14,753 — — — — 7,648 22,401 7,648 Warrants and rights 3,719 2,173 (b) (d) — — (4,118 ) 743 2,517 510 Trade claims 562 — — 5,865 (611 ) 134 5,950 202 Lehman claim 265 — — — — 36 301 36 Contingent consideration liability 5,997 — — — (392 ) (2,165 ) 3,440 (2,165 ) Consolidated Funds Preferred stock 36,928 22,644 (f) (13,668 ) (a) 8,437 (11,903 ) 8,007 50,445 3,896 Common stocks 295 — — 526 (848 ) 77 50 — Warrants and rights 3 — — — — 3,565 3,568 3,565 Term Loan 657 — — 202 (1,021 ) 162 — — Year Ended December 31, 2016 Balance at December 31, 2015 Transfers in Transfers out Purchases/(covers) (Sales)/shorts Realized and Unrealized gains/losses Balance at December 31, 2016 Change in unrealized gains/losses relating to instruments still held (1) (dollars in thousands) Operating Entities Preferred stock $ 12,872 $ — $ (1,000 ) (a) $ 3,717 $ (218 ) $ 440 $ 15,811 $ 34 Common stocks 2,278 — — 7,099 (3,222 ) 3,966 10,121 3,972 Convertible bonds 819 — — — (569 ) — 250 — Options, asset 18,194 — — — — (3,441 ) 14,753 (3,441 ) Options, liability 18,194 — — — — (3,441 ) 14,753 (3,441 ) Warrants and rights 2,572 — — 1,914 (817 ) 50 3,719 79 Trade Claims — 675 (e) — 289 (325 ) (77 ) 562 (111 ) Lehman claim 299 — — — — (34 ) 265 (35 ) Contingent consideration liability 6,158 — — 2,397 (4,697 ) 2,139 5,997 — Consolidated Funds Preferred stock 32,000 — (11,000 ) (a) 13,483 — 2,445 36,928 2,445 Common Stock — — — 314 — (19 ) 295 (19 ) Warrants and rights — — — — — 3 3 3 Term Loan — — — 590 — 67 657 67 (1) Unrealized gains/losses are reported in other income (loss) in the accompanying consolidated statements of operations. (a) The investments were converted to common stock. (b) The Company received warrants as part of a transaction. (c) The entity in which the Company is invested completed an initial public offering. (d) As part of the preferred stock sale, the sellers received contingent value rights to be paid in the event certain milestones are reached. (e) The investment undertook a reorganization and subsequently is not traded in an active market. (f) The Company transferred investments to a consolidated fund. All realized and unrealized gains (losses) in the table above are reflected in other income (loss) in the accompanying consolidated statements of operations. Certain assets and liabilities are measured at fair value on a nonrecurring basis and therefore are not included in the tables above. The Company recognizes all transfers and the related unrealized gain (loss) at the beginning of the reporting period. Transfers between level 1 and 2 generally relate to whether the principal market for the security becomes active or inactive. Transfers between level 2 and 3 generally relate to whether significant relevant observable inputs are available for the fair value measurements or due to change in liquidity restrictions for the investments. During the years ended December 31, 2017 and 2016, there were no transfers between level 1 and level 2 assets and liabilities. The following table includes quantitative information as of December 31, 2017 and 2016 for financial instruments classified within level 3. The table below quantifies information about the significant unobservable inputs used in the fair value measurement of the Company's level 3 financial instruments. Quantitative Information about Level 3 Fair Value Measurements Fair Value at December 31, 2017 Valuation techniques Unobservable Inputs Range Level 3 Assets (dollars in thousands) Common and preferred stocks $ 5,642 Guideline companies/transaction price Market multiples 4.8x to 8.5x Trade claims 70 Discounted cash flows Discount rate 20% Warrants and rights 2,516 Model based Discounted cash flows Volatility Discount rate 61% 22% Options 1,455 Option pricing models Volatility 28% Other level 3 assets (a) 70,570 Total level 3 assets 80,253 Level 3 Liabilities Options 22,401 Option pricing models Volatility 28% Contingent consideration liability 3,440 Discounted cash flows Projected cash flow and discount rate 8% - 23% (weighted average 22%) Total level 3 liabilities $ 25,841 Quantitative Information about Level 3 Fair Value Measurements Fair Value at December 31, 2016 Valuation techniques Unobservable Inputs Range Level 3 Assets (dollars in thousands) Common and preferred stocks $ 10,917 Guideline companies/transaction price Option pricing method, discounted cash flow Volatility Market multiples Discount rate 37% 0.8x to 9.3x 9.5% to 10% Trade claims 520 Discounted cash flows Market multiples Discount rate 6x 20% Warrants and rights 3,719 Model based Volatility 30% to 85% (weighted average 73%) Options 14,753 Option pricing models Volatility 40% Other level 3 assets (a) 53,455 Total level 3 assets 83,364 Level 3 Liabilities Options 14,753 Option pricing models Volatility 40% Contingent consideration liability 5,997 Discounted cash flows Projected cash flow and discount rate 8% - 25% Total level 3 liabilities $ 20,750 (a) The quantitative disclosures exclude financial instruments for which the determination of fair value is based on prices from recent transactions. The Company has established valuation policies and procedures and an internal control infrastructure over its fair value measurement of financial instruments which includes ongoing oversight by the valuation committee as well as periodic audits performed by the Company's internal audit group. The valuation committee is comprised of senior management, including non-investment professionals, who are responsible for overseeing and monitoring the pricing of the Company's investments, including the review of the results of the independent price verification process, approval of new trading asset classes and use of applicable pricing models and approaches. The US GAAP fair value leveling hierarchy is designated and monitored on an ongoing basis. In determining the designation, the Company takes into consideration a number of factors including the observability of inputs, liquidity of the investment and the significance of a particular input to the fair value measurement. Designations, models, pricing vendors, third party valuation providers and inputs used to derive fair market value are subject to review by the valuation committee and the internal audit group. The Company reviews its valuation policy guidelines on an ongoing basis and may adjust them in light of, improved valuation metrics and models, the availability of reliable inputs and information, and prevailing market conditions. The Company reviews a daily profit and loss report, as well as other periodic reports, and analyzes material changes from period-to-period in the valuation of its investments as part of its control procedures. The Company also performs back testing on a regular basis by comparing prices observed in executed transactions to previous valuations. The fair market value for level 3 securities may be highly sensitive to the use of industry standard models, unobservable inputs and subjective assumptions. The degree of fair market value sensitivity is also contingent upon the subjective weight given to specific inputs and valuation metrics. The Company holds various equity and debt instruments where different weight may be applied to industry standard models representing standard valuation metrics such as: discounted cash flows, market multiples, comparative transactions, capital rates, recovery rates and timing, and bid levels. Generally, changes in the weights ascribed to the various valuation metrics and the significant unobservable inputs in isolation may result in significantly lower or higher fair value measurements. Volatility levels for warrants and options are not readily observable and subject to interpretation. Changes in capital rates, discount rates and replacement costs could significantly increase or decrease the valuation of the real estate investments. The interrelationship between unobservable inputs may vary significantly amongst level 3 securities as they are generally highly idiosyncratic. Significant increases (decreases) in any of those inputs in isolation can result in a significantly lower (higher) fair value measurement. Other financial assets and liabilities The following table presents the carrying values and fair values, at December 31, 2017 and 2016 , of financial assets and liabilities and information on their classification within the fair value hierarchy which are not measured at fair value on a recurring basis. For additional information regarding the financial instruments within the scope of this disclosure, and the methods and significant assumptions used to estimate their fair value see Note 3 . December 31, 2017 December 31, 2016 Fair Value Hierarchy Carrying Amount Fair Value Carrying Amount Fair Value (dollars in thousands) Financial Assets Operating companies Cash and cash equivalents $ 130,052 $ 130,052 $ 110,990 $ 110,990 Level 1 Cash collateral pledged 17,888 17,888 13,342 13,342 Level 2 Segregated cash 116,268 116,268 1,024 1,024 Level 1 Securities borrowed 443,148 414,763 — — Level 2 Loans receivable 37,993 37,993 (d) 31,088 31,088 (d) Level 3 Consolidated funds Cash and cash equivalents 21,988 21,988 17,761 17,761 Level 1 Financial Liabilities Securities loaned 456,831 440,162 — — Level 2 Convertible debt 141,502 (a) 172,709 (b) 130,029 (a) 149,545 (b) Level 2 Notes payable and other debt 173,458 182,352 (c) 77,030 80,817 (c) Level 2 (a) The carrying amount of the convertible debt includes an unamortized discount of $25.6 million and $17.8 million as of December 31, 2017 and 2016 , respectively. (b) The convertible debt includes the conversion option and is based on the last broker quote available. (c) Notes payable and other debt are based on the last broker quote available. (d) The fair market value of level 3 loans is calculated using discounted cash flows.

Deposits with Clearing Organiza

Deposits with Clearing Organizations, Brokers and Banks	12 Months Ended
	Dec. 31, 2017
Deposits with Clearing Organizations, Brokers and Banks [Abstract]
Deposits with Clearing Organizations, Brokers and Banks	Deposits with Clearing Organizations, Brokers and Banks Under the terms of agreements between the Company and some of its clearing organizations, brokers and banks, balances owed are collateralized by certain of the Company’s cash and securities balances. As of December 31, 2017 and 2016 , the Company had a total of $94.0 million and $8.9 million , respectively, in deposit accounts with clearing organizations, brokers and banks that could be used as collateral to offset losses incurred by the clearing organizations, brokers and banks, on behalf of the Company’s activities, if such losses were to occur.

Receivables from and payables t

Receivables from and payables to brokers, dealers and clearing organizations	12 Months Ended
	Dec. 31, 2017
Brokers and Dealers [Abstract]
Due to and from Broker-Dealers and Clearing Organizations Disclosure [Text Block]	Receivables From and Payables to Brokers, Dealers and Clearing Organizations Receivables from and payable to brokers, dealers and clearing organizations includes cash held at the clearing brokers, amounts receivable or payable for unsettled transactions, monies borrowed and proceeds from short sales equal to the fair value of securities sold, not yet purchased, which are restricted until the Company purchases the securities sold short. Pursuant to the master netting agreements the Company entered into with its brokers, dealers and clearing organizations, these balances are presented net (assets less liabilities) across balances with the same counterparty. The Company's receivables from and payables to brokers, dealers and clearing organizations balances are held at multiple financial institutions. As of December 31, 2017 and 2016 , amounts receivable from brokers, dealers and clearing organizations include: As of December 31, 2017 2016 (dollars in thousands) Broker-dealers $ 409,499 $ 78,898 Securities failed to deliver 87,820 — Clearing organizations 6,126 — Stock borrow interest receivable 4,733 — $ 508,178 $ 78,898 As of December 31, 2017 and 2016 , amounts payable to brokers, dealers and clearing organizations include: As of December 31, 2017 2016 (dollars in thousands) Broker-dealers $ 145,860 $ 210,309 Securities failed to receive 53,540 — Clearing organizations 48,257 — Stock loan interest payable 4,496 — $ 252,153 $ 210,309

Receivable from and Payable to

Receivable from and Payable to Customers	12 Months Ended
	Dec. 31, 2017
Receivables and Payable to Customers [Abstract]
Payable to Customers [Text Block]	Receivable From and Payable to Customers As of December 31, 2017 , receivable from customers of $49.9 million consists of amounts owed by customers relating to securities transactions not completed on settlement date and receivables arising from the prepayment of a Commission Sharing Agreement (“CSA”), net of an allowance for doubtful accounts. A prepaid CSA is established for research-related disbursements in advance of anticipated customer commission volumes. Such receivables may not be evidenced by contractual obligations. As of December 31, 2017 , payable to customers of $352.5 million include amounts due on cash and margin transactions to the Company's clients, some of which have their assets held by a Company omnibus account, which are included within receivables from brokers, dealers and clearing organizations in the accompanying consolidated statements of financial condition. In the omnibus structure, positions that are owned by Cowen International Ltd are fully cross collateralized by client funds, meaning that the Company, for all intents and purposes, has no market risk. Additionally, Cowen International Ltd has no obligation to settle any trade that it deems inappropriate from a risk perspective, adding an important market and counterparty risk mitigating factor.

Fixed Assets

Fixed Assets	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Fixed Assets	Fixed Assets As of December 31, 2017 and 2016 , fixed assets consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Telephone and computer equipment $ 3,465 $ 2,787 Computer software 2,914 2,167 Furniture and fixtures 1,423 1,204 Leasehold improvements 36,702 35,092 Assets acquired under capital leases—equipment 6,920 4,075 Aircraft and related equipment 17,369 20,893 Other 58 57 68,851 66,275 Less: Accumulated depreciation and amortization (28,355 ) (23,867 ) $ 40,496 $ 42,408 Depreciation and amortization expense related to fixed assets was $7.0 million , $7.7 million and $6.8 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively and are included in depreciation and amortization expense in the accompanying consolidated statements of operations. On April 22, 2016, the Company entered into a transaction whereby the Company acquired a portfolio of four specialized aircraft which were on lease (See Note 2 ). During the year ended December 31, 2016, the Company purchased two aircraft and entered into two additional lease agreements. As of December 31, 2017 and 2016 , aircraft and related equipment of $17.4 million and $20.9 million , respectively, is held for leasing purposes. One of the planes were sold during the third quarter of 2017 for a gain of $2.3 million . Depreciation expense related to leased assets was $1.5 million and $1.7 million for the year ended December 31, 2017 and 2016 , respectively. As of December 31, 2017 and 2016, the accumulated depreciation related to leased assets was $1.8 million and $1.7 million , respectively. Assets acquired under capital leases were $6.9 million and $4.1 million as of December 31, 2017 and 2016 , respectively. If the assets acquired under capital leases transfer title at the end of the lease term or contain a bargain purchase option, the assets are amortized over their estimated useful lives; otherwise, the assets are amortized over the respective lease term. The depreciation of assets capitalized under capital leases is included in depreciation and amortization expenses and was $1.0 million , $1.2 million , and $1.5 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. As of December 31, 2017 and 2016, accumulated depreciation related to assets acquired under capital leases was $3.4 million and $2.4 million respectively.

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	Goodwill and Intangible Assets Goodwill In accordance with US GAAP, the Company tests goodwill for impairment on an annual basis or at an interim period if events or changed circumstances would more likely than not reduce the fair value of a reporting unit below its carrying amount. Under US GAAP, the Company first assesses the qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amounts as a basis for determining if it is necessary to perform the two-step approach. Periodically estimating the fair value of a reporting unit requires significant judgment and often involves the use of significant estimates and assumptions. These estimates and assumptions could have a significant effect on whether or not an impairment charge is recorded and the magnitude of such a charge. The Company estimated the fair value using the income and market approach which involves estimates of future cash flows, discount rates, economic forecast and other assumption which are then used in the market approach (earning and / or transactions multiples) and / or income approach (discounted cash flow method). In connection with the CRT transaction (See Note 2 ), in May 2016, the Company recognized goodwill of $3.5 million . Goodwill, which primarily relates to expected synergies from combining operations, is fully deductible for tax purposes and has been assigned to the broker-dealer segment of the Company. On September 23, 2016, the Company and the portfolio managers of RASL completed the sale of their respective ownership interests in RASL, an investment advisor. In contemplation with the sale transaction, the Company allocated $1.2 million of goodwill to the RASL disposal group (See Note 2 ) which was included in the investment management reporting unit. Based on the results of the impairment analysis as of December 31, 2017 , the Company did not recognize any impairment relating to the investment management or broker-dealer reporting units. No impairment charges for goodwill were recognized during the years ended December 31, 2016 and 2015, respectively. The following table presents the changes in the Company's goodwill balance, by reporting unit for the years ended December 31, 2017 , 2016 , and 2015 : Investment Management Broker- Total (dollars in thousands) Beginning balance - December 31, 2015 Goodwill $ 30,228 $ 47,818 $ 78,046 Accumulated impairment charges (10,200 ) (9,485 ) (19,685 ) Net 20,028 38,333 58,361 Activity: 2016 Recognized goodwill — 3,519 3,519 Goodwill allocated to disposal group (1,202 ) — (1,202 ) Goodwill impairment charges — — — Ending balance: December 31, 2016 Goodwill 29,026 51,337 80,363 Accumulated impairment charges (10,200 ) (9,485 ) (19,685 ) Net 18,826 41,852 60,678 Activity: 2017 Recognized goodwill — — — Goodwill allocated to disposal group — — — Goodwill impairment charges — — — Ending balance: December 31, 2017 Goodwill 29,026 51,337 80,363 Accumulated impairment charges (10,200 ) (9,485 ) (19,685 ) Net $ 18,826 $ 41,852 $ 60,678 Intangible assets Information for the Company's intangible assets that are subject to amortization is presented below as of December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (in years) (in thousands) (in thousands) Trade names 0.6 - 7.5 $ 10,622 $ (10,555 ) $ 67 $ 9,962 $ (9,689 ) $ 273 Customer relationships 3 - 14 41,134 (15,733 ) 25,401 33,874 (12,948 ) 20,926 Customer contracts 1.2 800 (800 ) — 800 (800 ) — Non compete agreements and covenants with limiting conditions acquired 3 - 5 2,237 (1,479 ) 758 2,268 (818 ) 1,450 Intellectual property 3 - 10 8,243 (4,514 ) 3,729 8,283 (5,163 ) 3,120 $ 63,036 $ (33,081 ) $ 29,955 $ 55,187 $ (29,418 ) $ 25,769 The Company tests intangible assets for impairment if events or circumstances suggest that the asset groups carrying value may not be fully recoverable. For the years ended December 31, 2017 and 2016 , no impairment charge for intangible assets was recognized. In connection with the CRT transaction (See Note 2), in May 2016, the Company recognized intangible assets (including customer relationships, trade name, intellectual property and non-compete arrangements) with an estimated fair value of $5.1 million which are included within intangible assets, net in the consolidation statements of financial condition with the expected useful lives ranging from 1 to 9 years with a weighted average useful life of 8.1 years. In connection with Convergex acquisition (See Note 2), in June 2017, the Company recognized intangible assets (including customer relationships, trade name, and intellectual property) with an estimated fair value of $ 10.3 million which are included within intangible assets, net in the consolidation statements of financial condition with the expected useful lives ranging from 0.6 years to 9.0 years with a weighted average useful life of 7.7 years . Amortization expense related to intangible assets was $6.1 million , $5.0 million , and $2.7 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively, which is included in depreciation and amortization expense in the accompanying consolidated statements of operations. All of the Company's intangible assets have finite lives. The estimated future amortization expense for the Company's intangible assets as of December 31, 2017 is as follows: (dollars in thousands) 2018 $ 4,946 2019 4,168 2020 3,950 2021 3,890 2022 3,108 Thereafter 9,893 $ 29,955

Other Assets

Other Assets	12 Months Ended
	Dec. 31, 2017
Other Assets [Abstract]
Other Assets	Other Assets Other assets in Operating Entities are as follows: As of December 31, 2017 2016 (dollars in thousands) Prepaid expenses $ 13,267 $ 10,669 Deposits 877 5,322 Reinsurance receivables, net (d) 14,014 5,187 Loan receivable (a) — 3,700 Tax receivables 1,457 3,267 Redemption Receivable 19,565 — Interest and dividends receivable 1,021 718 Deferred acquisition costs (c) 1,978 677 Deferred rent asset — 52 Military loan (b) 19,851 4,476 Other 16,238 4,338 $ 88,268 $ 38,406 (a) As of December 31, 2016, the maturity was August 2017 with interest rate of 12% . (b) As of December 31, 2017, the maturity is January 2024, with interest rate of 8% for the first five years and 8.5% for the remainder of the term, related to the Company's commercial reinsurance activities. As of December 31, 2016, the maturity is January 2024, with interest rate of 8% for the first five years and 8.5% for the remainder of the term, related to the Company's commercial reinsurance activities. (c) Balances relate to the Company's reinsurance business entered into during 2016 (See Note 17 ).

Accounts Payable Accrued Expens

Accounts Payable Accrued Expenses and Other Liabilities	12 Months Ended
	Dec. 31, 2017
Accounts Payable, Accrued Expenses and Other Liabilities [Abstract]
Accounts Payable Accrued Expenses and Other Liabilities	Accounts Payable, Accrued Expenses and Other Liabilities Accounts payable, accrued expenses and other liabilities in Operating Entities are as follows: As of December 31, 2017 2016 (dollars in thousands) Deferred rent obligations (see Note 3(k)) $ 12,822 $ 10,335 Contingent consideration payable (see Note 2) 3,440 5,997 Equity in RCG Longview Partners II, LLC (see Note 5a(3)) 6,022 5,948 Interest and dividends payable 2,891 3,541 Loss reserves and claims incurred but not reported (a) 9,464 3,455 Professional fees payable 5,008 3,143 Unearned premiums (a) 6,116 2,375 Fees payable 798 1,093 Accrued tax liabilities 7,482 456 Litigation reserve 3,000 — Accrued expenses and accounts payable (b) 39,490 11,182 $ 96,533 $ 47,525 (a) Balances relate to the Company's reinsurance business entered into during 2016 (See Note 17 ). (b) As of December 31, 2017, the balance includes premiums accrued but not yet paid of $18.0 million related to the Company’s reinsurance business.

Commission Management Payable

Commission Management Payable	12 Months Ended
	Dec. 31, 2017
Commission Management Payable [Abstract]
Commission management payable [Text Block]	Commission Management Payable The Company receives a gross commission from various clearing brokers, which is then used to fund commission sharing and recapture arrangements, less the portion retained as income to the Company. Accrued commission sharing and commission recapture payable of $70.5 million as of December 31, 2017 and $3.6 million as of December 31, 2016 are classified as commission management payable in the accompanying consolidated statements of financial condition.

Redeemable Non-Controlling Inte

Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds	Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds Redeemable non-controlling interests in consolidated subsidiaries and funds and the related net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds are comprised as follows: As of December 31, 2017 As of December 31, 2016 (dollars in thousands) Redeemable non-controlling interests in consolidated subsidiaries and funds Operating companies $ 6,113 $ 7,638 Consolidated Funds 434,491 371,567 $ 440,604 $ 379,205 Year Ended December 31, 2017 2016 2015 (dollars in thousands) Income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds Operating companies $ 2,353 $ 3,717 $ 9,503 Consolidated Funds 21,438 3,165 5,743 $ 23,791 $ 6,882 $ 15,246

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2017
Reinsurance [Abstract]
Reinsurance	Reinsurance The Company’s wholly-owned Luxembourg subsidiary, Hollenfels Re SA (“Hollenfels”) provides reinsurance to third party insurance and reinsurance companies. As Hollenfels started its operations during 2016, all claims it experienced (reported or not reported) were from the 2016 and 2017 accident years. During the year ended December 31, 2017 , Hollenfels’s share of incurred and paid claims, as reported to it by the underlying insurance and reinsurance companies, amounted to $15.3 million . During the same period, Hollenfels’s share of claims incurred but not reported plus expected development on reported claims totaled $5.8 million . Hollenfels generally employs an estimation methodology whereby historical average claims ratios over a period of 5 or 10 years, based on availability of data, are utilized. In cases where an event may have occurred that could give rise to claims in excess of the amount calculated using the above-mentioned methodology, then actuarial methods are used to calculate the impact of such an event. During the year, Hollenfels did not change its methodology for determining claim liability or claim adjustment expenses and calculated them using the above-mentioned methods. While Hollenfels typically settles its premiums and claim payments on a quarterly basis, the frequency of claims in the underlying policies is impractical for Hollenfels to obtain. This is because certain contracts Hollenfels has written are on a quota-share basis while the other policies provide aggregate loss protection, rendering the collection of information for all underlying contracts impracticable. Hollenfels did not discount any of its reserves and did not cede any portion of its exposures during the year ended December 31, 2017 .

Other Revenues and Expenses

Other Revenues and Expenses	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Revenues and Expenses	Other Revenues and Expenses On September 23, 2016, the Company and the portfolio managers RASL completed the sale of their respective ownership interests in RASL (See Note 2 ). Along with the target working capital transferred at closing, the Company also allocated a portion of goodwill associated with the investment management segment to the sale price (See Note 12 ) which is shown net in other revenues in the accompanying consolidated statements of operations. Other expenses, during the years ended December 31, 2017 , 2016 , and 2015 , are primarily the general administrative expenses of the various operating company subsidiaries or the Consolidated Funds.

Share-Based Compensation and Em

Share-Based Compensation and Employee Ownership Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation and Employee Ownership Plans	Share-Based and Deferred Compensation and Employee Ownership Plans On December 5, 2016, the Company effected a one-for-four reverse stock split of the Company's class A and class B common stock. All share and per share information has been retroactively adjusted to reflect the reverse stock split. The Company issues share based compensation under the 2006 Equity and Incentive Plan, the 2007 Equity and Incentive Plan (both established prior to the November 2009 transaction between Ramius Capital Group LLC and Cowen) and the Cowen Group, Inc. 2010 Equity and Incentive Plan (collectively, the “Equity Plans”). The Equity Plans permit the grant of options, restricted shares, restricted stock units, stock appreciation rights ("SAR's") and other equity based awards to the Company's employees and directors. Stock options granted generally vest over two -to- five -year periods and expire seven years from the date of grant. Restricted shares and restricted share units issued may be immediately vested or may generally vest over a two -to- five -year period. SAR's vest and expire after five years from grant date. Awards are subject to the risk of forfeiture. As of December 31, 2017 , there were no shares available for future issuance under the Equity Plans. Under the 2010 Equity Plan, the Company awarded $24.1 million of deferred cash awards to its employees during the year ended December 31, 2017 . These awards vest over a four year period and accrue interest at 0.70% per year. As of December 31, 2017 , the Company had unrecognized compensation expense related to the 2010 Equity Plan deferred cash awards of $35.0 million . Subsequent to the acquisition of Convergex Group (see Note 2 ) the Company maintained the Convergex Nonqualified Deferred Compensation Plan, which is a deferred cash award plan that is expensed over the 27 month service period requirement. As of December 31, 2017 , the Company had unrecognized compensation expense related to former Convergex Group deferred cash awards of $2.4 million . The Company measures compensation cost for share based awards according to the equity method. In accordance with the expense recognition provisions of those standards, the Company amortizes unearned compensation associated with share based awards on a straight-line basis over the vesting period of the option or award, net of estimated forfeitures. In relation to awards under the Equity Plans, the Company recognized compensation expense of $28.4 million , $26.0 million , and $21.7 million for the years ended December 31, 2017 , 2016 , and 2015 respectively. The income tax effect recognized for the Equity Plans was a benefit of $7.7 million , $11.4 million , and $5.0 million for the years ended December 31, 2017 , 2016 , and 2015 respectively. Stock Options and Stock Appreciation Rights The Company values options and SAR's on grant date using the Black-Scholes valuation model which requires the Company to make assumptions regarding the expected term, volatility, risk-free rate and dividend yield: Expected term . Expected term represents the period of time that awards granted are expected to be outstanding. The Company elected to use the "simplified" calculation method, as applicable to companies that lack extensive historical data. The mid-point between the vesting date and the contractual expiration date is used as the expected term under this method. Expected volatility . The Company bases its expected volatility on its own stock price history. Risk free rate . The risk-free rate for periods within the expected term of the award is based on the interest rate of a traded zero-coupon U.S. Treasury bond with a term equal to the awards' expected term on the date of grant. Dividend yield . The Company has not paid and does not expect to pay dividends in the foreseeable future. Accordingly, the assumed dividend yield is zero . The following table summarizes the Company's stock option activity for the years ended December 31, 2017 and 2016: Class A Common Shares Subject Weighted Average Weighted Average Aggregate Intrinsic (in years) (dollars in thousands) Balance outstanding at December 31, 2015 4,167 $ 19.56 1.6 $ 87 Options granted — — — — Options exercised — — — — Options expired — — — — Balance outstanding at December 31, 2016 4,167 $ 19.56 0.10 $ — Options granted — — — — Options exercised — — — — Options expired (4,167 ) 19.56 — — Balance outstanding at December 31, 2017 — $ — 0 $ — Options exercisable at December 31, 2016 4,167 $ 19.56 0.10 $ — Options exercisable at December 31, 2017 — $ — 0 $ — (1) Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016 . As of December 31, 2017 , the Company's stock options were fully expensed. The following table summarizes the Company's SAR's for the years ended December 31, 2017 : Class A Common Shares Subject Weighted Average Weighted Average Aggregate Intrinsic (in years) (dollars in thousands) Balance outstanding at December 31, 2015 100,000 $ 11.60 2.21 $ 558 SAR's granted — — — — SAR's acquired — — — — SAR's expired — — — — Balance outstanding at December 31, 2016 100,000 $ 11.60 1.21 $ 435 SAR's granted — — — — SAR's vested (25,000 ) 11.60 — — SAR's expired — — — — Balance outstanding at December 31, 2017 75,000 $ 11.60 0.21 $ 173 SAR's exercisable at December 31, 2016 — $ — — $ — SAR's exercisable at December 31, 2017 — $ — 0 $ — (1) Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016 . As of December 31, 2017 the unrecognized compensation expense related to the Company's grant of SAR's was an immaterial amount and at December 31, 2016 it was $0.1 million . Restricted Shares and Restricted Stock Units Granted to Employees Restricted shares and restricted stock units are referred to collectively as restricted stock. The following table summarizes the Company's restricted share and restricted stock unit activity for the years ended December 31, 2017 and 2016: Nonvested Restricted Class A Common Shares and Class A Common Restricted Stock Units Weighted-Average Balance outstanding at December 31, 2015 5,370,091 $ 16.68 Granted 2,157,403 14.02 Vested (1,487,092 ) 14.95 Canceled — — Forfeited (322,470 ) 14.89 Balance outstanding at December 31, 2016 5,717,932 $ 16.23 Granted 2,255,441 14.98 Vested (2,036,366 ) 14.64 Canceled — — Forfeited (357,714 ) 15.77 Balance outstanding at December 31, 2017 5,579,293 $ 16.33 Included in the restricted share and restricted stock unit activity are performance linked restricted stock units of 481,438 which were awarded to employees of the Company in December 2013 and January 2014. An additional 700,000 performance linked restricted stock units were awarded in March 2016. Of the awards granted, 109,375 have been forfeited through December 31, 2017 . The remaining awards, included in the outstanding balance as of December 31, 2017 , will vest between March 2019 and December 2020 and will be earned only to the extent that the Company attains specified market conditions relating to its volume-weighted average share price and total shareholder return in relation to certain benchmark indices and performance goals relating to aggregate net income and average return on shareholder equity. The actual number of RSUs ultimately earned could vary from zero , if performance goals are not met, to as much as 150% of the targeted award. Each RSU is equal to the one share of the Company’s Class A common stock. Compensation expense is recognized to the extent that it is probable that the Company will attain the performance goals. The fair value of restricted stock (excluding performance linked units which are valued using the Monte Carlo valuation model) is determined based on the number of shares granted and the quoted price of the Company's common stock on the date of grant. As of December 31, 2017 , there was $56.4 million of unrecognized compensation expense related to the Company's grant of nonvested restricted shares and restricted stock units to employees. Unrecognized compensation expense related to nonvested restricted shares and restricted stock units granted to employees is expected to be recognized over a weighted-average period of 2.27 years. Restricted Shares and Restricted Stock Units Granted to Non-employee Board Members There were 56,519 restricted stock units awarded during the year ended December 31, 2017 . As of December 31, 2017 there were 191,962 restricted stock units outstanding. There were 56,100 restricted stock units awarded during the year ended December 31, 2016. As of December 31, 2016 there were 162,176 restricted stock units outstanding.

Defined Contribution Plans

Defined Contribution Plans	12 Months Ended
	Dec. 31, 2017
Defined Contribution Plans [Abstract]
Defined Contribution Plans	Defined Contribution Plans The Company sponsors a Retirement and Savings Plan which is a defined contribution plan pursuant to Section 401(k) of the Internal Revenue Code (the "401(k) Plans"). All full-time employees of the Company can contribute on a tax deferred basis to the 401(k) Plans up to federal contribution limits or up to 100% of their annual compensation, subject to certain limitations. The Company provides matching contributions for certain employees that are equal to a specified percentage of the eligible participant's contribution as defined by the 401(k) Plans. For the years ended December 31, 2017, 2016 and 2015, the Company's contributions to the Plans were $0.7 million , $0.5 million and $0.5 million , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The taxable results of the Company’s U.S. operations are included in the consolidated income tax returns of Cowen Inc. as well as stand‑alone state and local tax returns. The Company has subsidiaries that are resident in foreign countries where tax filings have to be submitted on a stand‑alone basis. These subsidiaries are subject to tax in their respective countries and the Company is responsible for and, thus, reports all taxes incurred by these subsidiaries. The countries where the Company owns subsidiaries with tax filing obligations are the United Kingdom, Luxembourg, and Hong Kong. The components of the Company's income tax expense for the years ended December 31, 2017 , 2016 and 2015 are as follows: Year ended December 31, 2017 2016 2015 (dollars in thousands) Current tax expense/(benefit) Federal $ 421 $ 1,268 $ (635 ) State and local 2,034 1,972 313 Foreign 428 262 348 Total $ 2,883 $ 3,502 $ 26 Deferred tax expense/(benefit) Federal $ 44,071 $ (22,834 ) $ (37,979 ) State and local (2,938 ) (1,900 ) (7,420 ) Foreign 37 2,140 (2,123 ) Total 41,170 (22,594 ) (47,522 ) Total Tax expense/(benefit) $ 44,053 $ (19,092 ) $ (47,496 ) Consolidated U.S. income/(loss) before income taxes was $3.9 million in 2017, $(29.5) million in 2016, and $8.0 million in 2015. The corresponding amounts for non-U.S.-based income/(loss) were $3.1 million in 2017, $(2.0) million in 2016, and $3.5 million in 2015. The reconciliations of the Company's federal statutory rate to the effective income tax rate for the years ended December 31, 2017 , 2016 , and 2015 are as follows: Year ended December 31, 2017 2016 2015 Pre-tax loss at U.S. statutory rate 35.0 % 35.0 % 35.0 % Dividend received deduction (25.9 ) — — Bargain purchase gain (34.8 ) — — Basis adjustment on investments 65.2 — — Nondeductible expenses 14.2 — — Deferred asset recognition — — (323.8 ) Unrecognized gains on foreign subsidiaries — 38.7 — Change in valuation allowance — (6.7 ) — Impact of tax law change 669.8 — (27.9 ) State and foreign tax 25.3 1.3 (39.6 ) Reversal of income attributable to redeemable non-controlling interests (119.6 ) 1.3 (46.5 ) Other, net 3.7 (9.0 ) (11.0 ) Total 632.9 % 60.6 % (413.8 )% As of December 31, 2017 , the Company has net income taxes receivable of approximately $0.1 million representing federal tax overpayments, which is included in other assets on the accompanying consolidated statements of financial condition. The Company also has state and foreign income taxes payable of approximately $6.3 million , which is included in other liabilities on the accompanying consolidated statements of financial condition. The components of the Company's deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows: As of December 31, 2017 2016 (dollars in thousands) Deferred tax assets, net of valuation allowance Net operating loss $ 78,650 $ 126,037 Deferred compensation 39,992 44,966 Goodwill 1,042 4,758 Option liability 5,776 — Fixed assets — 3,541 Tax credits 4,419 2,898 Acquired lease liability 3,473 4,111 Other 2,696 2,238 Total deferred tax assets 136,048 188,549 Valuation allowance (2,103 ) (2,119 ) Deferred tax assets, net of valuation allowance 133,945 186,430 Deferred tax liabilities Unrealized gains on investments (7,523 ) (20,774 ) Amortization of bond discount (6,402 ) — Other (3,697 ) — Total deferred tax liabilities (17,622 ) (20,774 ) Deferred tax assets/(liabilities), net $ 116,323 $ 165,656 Deferred tax assets, net of valuation allowance, are reported in the accompanying consolidated statements of financial condition. In addition to the deferred tax balances in the table above, the Company records balances related to its operating losses in Luxembourg, which are discussed below. The Company records deferred tax assets and liabilities for the future tax benefit or expense that will result from differences between the carrying value of its assets for income tax purposes and for financial reporting purposes, as well as for operating or capital loss and tax credit carryovers. A valuation allowance is recorded to bring the net deferred tax assets to a level that, in management’s view, is more likely than not to be realized in the foreseeable future. This level will be estimated based on a number of factors, especially the amount of net deferred tax assets of the Company that are actually expected to be realized, for tax purposes, in the foreseeable future. The Company recorded approximately $2.1 million valuation allowance against its deferred tax assets of $136.0 million as of December 31, 2017 and recorded approximately $2.1 million valuation allowance against its deferred tax assets of $188.5 million as of December 31, 2016 . Separately, the Company has deferred tax liabilities of $17.6 million as of December 31, 2017 , and $20.8 million as of December 31, 2016 . For the year 2017, the Company’s total deferred tax expense is $41.2 million predominantly related to the impact of the Tax Cuts and Jobs Act, discussed in detail below, and the reversal of timing differences in the normal course of business. The deferred tax benefit of $22.6 million in 2016 was derived by the release of deferred tax liabilities related to the previous acquisitions by a local subsidiary, and reversal of temporary items during the course of normal operations. The deferred tax benefit of $47.5 million in 2015 mainly represented the deferred tax benefits generated by an acquisition of a local subsidiary. The Company has the following net operating loss carryforwards at December 31, 2017 : Federal New York State New York City Hong Kong Jurisdiction: Net operating loss (in millions) $248.4 $93.4 $130.8 $12.8 Year of expiration 2036 2036 2036 Indefinite In addition to the net operating loss carryforwards in the table above, the Company also has net operating loss carryforwards in Luxembourg. These loss carryforwards are only accessible to the extent of taxable income generated by the Luxembourg reinsurance companies, including any deferred income that will be generated in the future. Consequently, the Company recorded a deferred tax asset of $146.0 million , net of deferred tax liabilities of $349.1 million in connection with future taxable income, and an offsetting valuation allowance of $146.0 million against its Luxembourg net operating loss carryforwards that are in excess of such taxable income. The Company underwent a change of control under Section 382 of the Internal Revenue Code (“Section 382”) on November 2, 2009. Accordingly, a portion of the Company’s deferred tax assets, in particular a portion of its net operating loss, are subject to an annual limitation. The deduction limitation is approximately $2.4 million annually and applies to approximately $1.8 million of pre-transaction losses. Further, as a result of an acquisition of a subsidiary with net operating loss carryovers in June 2011, a portion of the Company’s deferred tax assets, are subject to an annual limitation under Section 382. The deduction limitation is approximately $6.7 million annually and applies to approximately $50.1 million of net operating losses. The Company is not expected to lose any deferred tax assets as a result of these limitations. The components of unrecognized tax benefits are as follows: As of December 31, 2017 2016 (dollars in thousands) Beginning balance at January 1 $ — $ — Increases due to acquisition 2,847 — Increases due to current year positions 1,100 — Ending balance at December 31 $ 3,947 $ — The amount of the unrecognized tax benefits of $3.9 million that would impact the effective tax rate of the Company is $1.1 million . The total amount of income tax-related interest and penalties recognized in the consolidated statement of operations for the year ended December 31, 2017 is expense of $0.3 million . The total amount of income tax-related interest and penalties recognized in the consolidated statement of financial condition at December 31, 2017 is $ 1.5 million . The Company is subject to examination by the United States Internal Revenue Service as well as state, local and foreign tax authorities in jurisdictions where the Company has significant business operations, such as New York, United Kingdom, and Luxembourg. Currently, the Company is under audit by the Internal Revenue Service for the 2014 tax year, and New York State for the 2010 to 2012 tax years. Management is not expecting a material tax liability from these audits. The Company continues to permanently reinvest the capital and accumulated earnings of its United Kingdom and Hong Kong subsidiaries. Effects of the Tax Cuts and Job Act New tax legislation, commonly referred to as the Tax Cuts and Jobs Act, was enacted on December 22, 2017. ASC 740, Accounting for Income Taxes , requires companies to recognize the effect of tax law changes in the period of enactment even though the effective date for most provisions is for tax years beginning after December 31, 2017, or in the case of certain other provisions, January 1, 2018. Given the significance of the legislation, the SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118), which allows registrants to record provisional amounts during a one year “measurement period” similar to that used when accounting for business combinations. However, the measurement period is deemed to have ended earlier when the registrant has obtained, prepared and analyzed the information necessary to finalize its accounting. During the measurement period, impacts of the law are expected to be recorded at the time a reasonable estimate for all or a portion of the effects can be made, and provisional amounts can be recognized and adjusted as information becomes available, prepared or analyzed. The SAB summarizes a three-step process to be applied at each reporting period to account for and qualitatively disclose: (1) the effects of the change in tax law for which accounting is complete; (2) provisional amounts (or adjustments to provisional amounts) for the effects of the tax law where accounting is not complete, but that a reasonable estimate has been determined; and (3) a reasonable estimate cannot yet be made and therefore taxes are reflected in accordance with law prior to the enactment of the Tax Cuts and Jobs Act. The new law includes a reduction in the U.S. corporate income tax rate from 35% to 21% . This change resulted in the Company reporting a deferred income tax expense of $46.6 million in 2017 due to the re-measurement of its deferred tax assets using the new 21% rate applicable upon reversal of these items. This accounting estimate for this matter is complete. The new law includes a one-time mandatory repatriation transition tax on the net accumulated earnings and profits of a U.S. taxpayer’s foreign subsidiaries. The Company has performed an earnings and profits analysis of its foreign subsidiaries, and as a result of accumulated deficits, there is no current or deferred income tax effect in this period. Therefore, the accounting estimate for this matter is complete. The new law includes commissions and performance based compensation in determining the excessive compensation limitation. This calculation could impact the deductibility of certain compensation related deferred tax assets. The Company analyzed the deferred tax assets related to commission and performance based compensation and concluded that no adjustments were required. Therefore, the accounting estimate for this matter is complete. The Company has evaluated other significant provisions of the law and has not identified any material impact these provisions may have on the Company's 2017 year-end financial statements. Management will continue to monitor the application of these provisions on the Company and make necessary policy elections if and when needed.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Lease Obligations The Company has entered into leases for office space and equipment. These leases contain rent escalation clauses. The Company records rent expense on a straight-line basis over the lease term, including any rent holiday periods. Rent expense was $22.6 million , $20.3 million and $18.5 million for the years ended December 31, 2017 , 2016 , and 2015, respectively and are included in occupancy and equipment expense in the accompanying consolidated statements of operations. As of December 31, 2017 , future minimum annual lease and service payments for the Company were as follows: Equipment Leases (a) Service Payments Facility Leases (b) (dollars in thousands) 2018 $ 3,511 $ 21,631 $ 25,960 2019 1,599 10,987 21,453 2020 669 1,539 17,626 2021 639 337 17,592 2022 420 — 11,942 Thereafter — — 7,354 $ 6,838 $ 34,494 $ 101,927 (a) Equipment Leases include the Company's commitments relating to operating and capital leases. See Note 23 for further information on the capital lease minimum payments which are included in the table. (b) The Company has entered into various agreements to sublease certain of its premises. The Company recorded sublease income related to these leases of $1.1 million , $2.2 million , and $2.3 million and for the years ended December 31, 2017 , 2016 , and 2015 respectively. Clawback Obligations For financial reporting purposes, the general partners of a real estate fund have recorded a liability for potential clawback obligations to the limited partners, due to changes in the unrealized value of the fund's remaining investments and where the fund's general partner has previously received carried interest distributions. The clawback liability, however, is not realized until the end of the fund's life. The life of the real estate funds with a potential clawback obligation is currently in a winding-up phase whereby the remaining assets of the fund are being liquidated as promptly as possible so as to maximize value, however a final date for liquidation has not been set. The fund is currently winding-down and as of both December 31, 2017 and 2016 , and the clawback obligation was $6.2 million . The Company serves as the general partner/managing member and/or investment manager to various affiliated and sponsored funds. As such, the Company is contingently liable for obligations for those entities. These amounts are not included above as the Company believes that the assets in these funds are sufficient to discharge any liabilities. Unfunded Commitments The following table summarizes unfunded commitments as of December 31, 2017 : Entity Unfunded Commitments Commitment term (dollars in millions) Real estate (a) $ 19.5 (a) HealthCare Royalty Partners funds (b) 6.2 2 years Eclipse Ventures Fund I, L.P. (formerly Formation8 Partners Hardware Fund I, L.P.) 0.4 7 years Lagunita Biosciences, LLC 2.0 3 years Eclipse Fund II, L.P. 0.9 8 years Eclipse Continuity Fund I, L.P. 0.6 9 years (a) The Company had unfunded commitments pertaining to capital commitments in six real estate investments held by the Company, all of which pertain to related party investments. Such commitments can be called at any time up to four years, subject to advance notice. (b) The Company is a limited partner of the HealthCare Royalty Partners funds (which are managed by Healthcare Royalty Management) and is a member of HealthCare Royalty Partners General Partners. The Company will make its pro-rata investment in the HealthCare Royalty Partners funds along with the other limited partners. Litigation In the ordinary course of business, the Company and its affiliates and subsidiaries and current and former officers, directors and employees (the "Company and Related Parties") are named as defendants in, or as parties to, various legal actions and proceedings. Certain of these actions and proceedings assert claims or seek relief in connection with alleged violations of securities, banking, anti-fraud, anti-money laundering, employment and other statutory and common laws. Certain of these actual or threatened legal actions and proceedings include claims for substantial or indeterminate compensatory or punitive damages, or for injunctive relief. In the ordinary course of business, the Company and Related Parties are also subject to governmental and regulatory examinations, information gathering requests (both formal and informal), certain of which may result in adverse judgments, settlements, fines, penalties, injunctions or other relief. Certain of our affiliates and subsidiaries are investment banks, registered broker-dealers, futures commission merchants, investment advisers or other regulated entities and, in those capacities, are subject to regulation by various U.S., state and foreign securities, commodity futures and other regulators. In connection with formal and informal inquiries by these regulators, we receive requests, and orders seeking documents and other information in connection with various aspects of our regulated activities. Due to the global scope of the Company's operations, and its presence in countries around the world, the Company and Related Parties may be subject to litigation, and governmental and regulatory examinations, information gathering requests, investigations and proceedings (both formal and informal), in multiple jurisdictions with legal and regulatory regimes that may differ substantially, and present substantially different risks, from those the Company and Related Parties are subject to in the United States. The Company seeks to resolve all litigation and regulatory matters in the manner management believes is in the best interests of the Company and its shareholders, and contests liability, allegations of wrongdoing and, where applicable, the amount of damages or scope of any penalties or other relief sought as appropriate in each pending matter. In accordance with US GAAP, the Company establishes reserves for contingencies when the Company believes that it is probable that a loss has been incurred and the amount of loss can be reasonably estimated. The Company discloses a contingency if there is at least a reasonable possibility that a loss may have been incurred and there is no reserve for the loss because the conditions above are not met. The Company's disclosure includes an estimate of the reasonably possible loss or range of loss for those matters, for which an estimate can be made. Neither a reserve nor disclosure is required for losses that are deemed remote . The Company appropriately reserves for certain matters where, in the opinion of management, the likelihood of liability is probable and the extent of such liability is reasonably estimable. Such amounts are included within accounts payable, accrued expenses and other liabilities in the accompanying consolidated statements of financial condition. Estimates, by their nature, are based on judgment and currently available information and involve a variety of factors, including, but not limited to, the type and nature of the litigation, claim or proceeding, the progress of the matter, the advice of legal counsel, the Company's defenses and its experience in similar cases or proceedings as well as its assessment of matters, including settlements, involving other defendants in similar or related cases or proceedings. The Company may increase or decrease its legal reserves in the future, on a matter-by-matter basis, to account for developments in such matters. The Company accrues legal fees as incurred. The following information reflects developments with respect to the Company’s legal proceedings that occurred during the year ended December 31, 2017. On December 27, 2013, Landol Fletcher filed a putative class action lawsuit against Convergex Holdings, LLC, Convergex Group, LLC, Cowen Execution, Convergex Global Markets Limited and G-Trade Services LLC (collectively, “Convergex”) in the United States District Court for the Southern District of New York (Landol Fletcher and all others similarly situated v. Convergex Group LLC, Cowen Execution, Convergex Global Markets Ltd., Convergex Holdings LLC, G-Trade Services LLC, & Does 1-10, No. 1:13-CV-09150-LLS). The suit alleges breaches of fiduciary duty and prohibited transactions under ERISA and seeks to maintain a class action on behalf of all ERISA plan participants, beneficiaries and named fiduciaries whose plans were impacted by net trading by Convergex Global Markets Limited from October 2006 to December 2011. On April 11, 2014, Landol Fletcher and Frederick P. Potter Jr., filed an amended complaint raising materially similar allegations. This matter was assumed by the Company as a result of the Company’s previously announced acquisition of Convergex Group, which was completed on June 1, 2017. On February 17, 2016, the District Court granted Convergex’s motion to dismiss the amended complaint. Plaintiffs filed an appeal to the Second Circuit, and the AARP and Department of Labor filed amicus briefs on plaintiffs' behalf. The appeal was argued on December 12, 2016. On February 10, 2017, the Second Circuit Court of Appeals (1) reversed the District Court, finding that plaintiff has constitutional standing in a “representative” capacity to sue for damages to the ERISA defined benefit plan in which he is a participant, and (2) remanded to the District Court to reconsider, in light of the Circuit Court’s decision, the issue whether plaintiff has standing to pursue claims on behalf of ERISA plans in which plaintiff is not a participant. Convergex filed a petition for rehearing, and the Court of Appeals denied the petition. On June 30, 2017, the Company filed a notice of motion and memorandum of law in support of a motion to stay the proceedings in the District Court pending resolution of its petition for writ of certiorari, which the Company intended to file with the U.S. Supreme Court. On August 16, 2017, the District Court granted the Company’s motion to stay the proceedings in the District Court pending resolution of the Company’s petition for writ of certiorari. On September 1, 2017, the Company filed a petition with the United States Supreme Court for a writ of certiorari requesting review of the decision of the Court of Appeals. On January 8, 2018, the U.S. Supreme Court denied the Company’s petition for a writ of certiorari. The previously granted stay of the proceedings in the District Court will now lift and the case will proceed in the District Court. We are indemnified against losses arising from this matter pursuant to, and subject to, the provisions of the purchase agreement relating to the acquisition of Convergex Group. Because the case is in its preliminary stages, the Company cannot predict the outcome at this time, but it does not currently expect this case to have a material effect on its financial position or its results of operations.

Convertible Debt and Notes Paya

Convertible Debt and Notes Payable	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Convertible Debt and Notes Payable	Convertible Debt and Notes Payable As of December 31, 2017 and 2016 , the Company's outstanding debt was as follows: As of December 31, 2017 2016 (dollars in thousands) Convertible debt $ 141,502 $ 130,029 Note payable 132,970 60,953 Term loan 28,121 — Other notes payable 8,247 14,237 Capital lease obligations 4,120 1,840 $ 314,960 $ 207,059 Convertible Debt 2022 Convertible Notes The Company, on December 14, 2017, issued $135.0 million a ggregate principal amount of 3.00% convertible senior notes due 2022 (the “2022 Convertible Notes”). The 2022 Convertible Notes are due on December 15, 2022 unless earlier repurchased by the Company or converted by the holder in accordance with their terms prior to such date. The interest on the 2022 Convertible Notes is payable semi-annually on December 15 and June 15 of each year. The notes are senior unsecured obligations of Cowen. The 2022 Convertible Notes may be converted into cash or shares of Class A common stock at the Company's election based on the current conversion price. The 2022 Convertible Notes were issued with an initial conversion price of $17.375 per share of Cowen’s Class A common stock. The Company used the net proceeds, together with cash on hand, from the offering for general corporate purposes, including the repurchase or repayment of $115.1 million of the Company’s outstanding 3.0% cash convertible senior notes due 2019 (the "2019 Convertible Notes") and the repurchase of approximately $19.5 million of the Company’s shares of its Class A common stock, which were consummated substantially concurrently with the closing of the offering. The Company recorded interest expense of $0.2 million for the year ended December 31, 2017 . The Company recognized the embedded cash conversion option at issuance date fair value, which also represents the initial unamortized discount on the 2022 Convertible Notes of $23.4 million and is shown net in convertible debt in the accompanying consolidated statements of financial condition. Amortization on the discount, included within interest expense in the accompanying consolidated statements of operations is $0.2 million for the year ended December 31, 2017 , based on an effective interest rate of 7.13% . The Company capitalized the debt issuance costs in the amount of $2.1 million , which is a direct deduction from the carrying value of the debt and will be amortized over the life of the 2022 Convertible Notes. 2019 Convertible Notes On March 10, 2014, the Company issued $149.5 million of 3.0% cash convertible senior notes (the "2019 Convertible Notes"). The 2019 Convertible Notes are due on March 15, 2019 unless earlier repurchased by the Company or converted by the holder into cash in accordance with their terms prior to such date. The interest on the 2019 Convertible Notes is payable semi-annually on March 15 and September 15 of each year. The 2019 Convertible Notes are senior unsecured obligations of the Company. The 2019 Convertible Notes may be converted into cash, upon the occurrence of certain events, whereby a holder will receive, per $1,000 principal amount of notes being converted, an amount equal to the sum of principal amount outstanding and the conversion amount based on the current conversion price (the "Conversion Option"). The 2019 Convertible Notes were issued with an initial conversion price of $21.32 per share (per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016). During December 2017, the Company repurchased and extinguished $115.1 million of the outstanding balance of the 2019 Convertible Notes. The Company recorded interest expense of $4.3 million , $4.5 million and $4.5 million for the years ended December 31, 2017 , 2016 and 2015, respectively. The initial unamortized discount on the 2019 Convertible Notes was $35.7 million and is shown net in convertible debt in the accompanying consolidated statements of financial condition. Amortization on the discount, included within interest expense in the accompanying consolidated statements of operations is $7.3 million , $6.9 million and $6.3 million for the years ended December 31, 2017 , 2016 , and 2015, respectively, based on an effective interest rate of 8.89% . The Company capitalized the debt issuance costs in the amount of $0.9 million , which is a direct deduction from the carrying value of the debt and will be amortized over the life of the 2019 Convertible Notes. In conjunction with the partial extinguishment of the 2019 Convertible Notes, the Company accelerated the pro-rata unamortized discount and capitalized debt issuance costs. The Company recognized $11.6 million of loss on debt extinguishment. Of the net proceeds from the sale of the 2019 Convertible Notes, approximately $20.5 million was applied to pay the net cost of a cash convertible note economic hedge and warrant transaction, which increased the effective conversion price to $28.72 (see Note 6 ) (per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016), and approximately $0.3 million was applied to repurchase shares of Cowen Class A common stock. The remainder of the net proceeds is being used for general corporate purposes. Note Payable 2027 Notes On December 8, 2017, the Company completed its public offering of $120 million of 7.35% senior notes due 2027 (the “2027 Notes”) and subsequently the underwriters exercised in full their option to purchase an additional $18.0 million principal amount of the 2027 Notes. Interest on the 2027 Notes is payable quarterly in arrears on March 15, June 15, September 15 and December 15. The Company recorded interest expense of $0.6 million for the year ended December 31, 2017 . The Company capitalized debt issuance costs of approximately $5.1 million w hich is a direct deduction from the carrying value of the debt and will be amortized over the life of the 2027 Notes. The net proceeds of the offering, after deducting the underwriting discount and estimated offering expenses payable by the Company were used to redeem all of its 8.25% senior notes due 2021 (the "2021 Notes") and for general corporate purposes. 2021 Notes The Company redeemed the Company's outstanding $63.25 million principal amount of the 2021 Notes, following which the 2021 Notes were delisted from NASDAQ. The redemption was made pursuant to the terms of the 2021 Notes and the indenture governing the 2021 Notes. The redemption price for the 2021 Notes was equal to 106.188% o f the principal amount of the 2021 Notes plus accrued and unpaid interest. The Company recorded interest expense of $5.3 million , $5.2 million and $5.2 million for the years ended December 31, 2017 , 2016, and 2015 respectively. In conjunction with the extinguishment of the 2021 Notes, the Company expensed the unamortized capitalized debt issuance costs. The Company recognized $5.6 million of loss on debt extinguishment. Term Loan On June 30, 2017, the Company borrowed $28.2 million to fund general corporate purposes. This term loan has an effective interest rate of LIBOR plus 3.75% with a lump sum payment of the entire principal amount due on June 29, 2018. The loan is secured by the value of the Company's limited partnership interests in two affiliated funds. The Company has provided a guarantee for this loan. The Company recorded interest expense of $0.7 million for the year ended December 31, 2017 . Other Notes Payable During January 2017, the Company borrowed $2.1 million to fund insurance premium payments. This note has an effective interest rate of 1.50% and is due on December 31, 2017, with monthly payment requirements of $0.2 million . As of December 31, 2017 , the note was fully repaid. Interest expense for the year ended December 31, 2017 was insignificant. The Company has entered into various financing for its aircraft. The aircraft financing, net of debt costs, is recorded in notes payable and short-term borrowings in the accompanying consolidated statements of financial condition. The debt maturities ranged from January 2019 to April 2021 and interest rates ranged from 4.21% to 7.25% . As of December 31, 2017 and 2016, the remaining balance on the aircraft financing agreements was $8.2 million and $14.4 million , respectively . Interest expense was $0.7 million and $0.8 million for the years ended December 31, 2017 and 2016, respectively. Capital Lease Obligations The Company has entered into a capital lease for computer equipment, which amounted to $6.9 million and is recorded in fixed assets as capital lease obligations. In addition, as part of the Convergex Group acquisition, the Company holds two capital leases for computer equipment which amounted to $0.8 million and are recorded as capital lease obligations. These capital lease obligations are included in short-term borrowings and other debt in the accompanying consolidated statements of financial condition, and have lease terms that range from 48 to 60 months and interest rates that range from 3.70% to 5.69% . As of December 31, 2017 , t he remaining balance on these capital leases was $4.1 million . Interest expense was $0.1 million , $0.1 million , $0.2 million for the years ended December 31, 2017 , 2016, and 2015, respectively. Annual scheduled maturities of debt and minimum payments (of principle and interest) for all debt outstanding as of December 31, 2017 , are as follows: Convertible Debt Note Payable Term loan Other Note Payable Capital Lease (dollars in thousands) 2018 $ 4,840 $ 10,340 $ — $ 2,032 $ 2,059 2019 38,925 10,143 28,901 3,410 717 2020 4,050 10,143 — 1,363 639 2021 4,050 10,143 — 2,512 639 2022 139,050 10,143 — — 420 Thereafter — 188,715 — — — Subtotal 190,915 239,627 28,901 9,317 4,474 Less (a) (49,413 ) (106,657 ) (780 ) (1,070 ) (354 ) Total $ 141,502 $ 132,970 $ 28,121 $ 8,247 $ 4,120 (a) Amount necessary to reduce net minimum payments to present value calculated at the Company's implicit rate at inception. This amount also includes capitalized debt costs and the unamortized discount on the convertible debt. Letters of Credit As of December 31, 2017 , the Company has eight irrevocable letters of credit, related to leased office space, for which there is cash collateral pledged and the Company pays a fee on the stated amount of the letter of credit. The Company also has pledged as collateral, $11.8 million , as of December 31, 2017 , and $5.5 million , as of December 31, 2016 , due between March 2018 and March 2021, for reinsurance agreements . Location Amount Maturity (dollars in thousands) Connecticut $ 65 January 2018 Boston $ 382 March 2018 New York $ 355 April 2018 New York $ 70 May 2018 New York $ 596 October 2018 New York $ 2,250 October 2018 New York $ 1,600 November 2018 San Francisco $ 710 January 2019 To the extent any letter of credit is drawn upon, interest will be assessed at the prime commercial lending rate . As of December 31, 2017 and 2016 , there were no amounts due related to these letters of credit .

Stockholder's Equity

Stockholder's Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholder's Equity	Stockholder's Equity On December 5, 2016, the Company effected a one-for-four reverse stock split of the Company's class A and class B common stock. All share and per share information has been retroactively adjusted to reflect the reverse stock split. In addition, there was a reclassification of $0.9 million from the par value of our class A common stock to additional paid-in capital to reflect the impact of the reverse stock split. The Company is authorized to issue 125,000,000 shares of common stock, which shall consist of 62,500,000 shares of Class A common stock, par value $0.01 per share, and 62,500,000 shares of Class B common stock, par value $0.01 per share. The Company is also authorized to issue 10,000,000 shares of preferred stock, par value $0.01 per share. Subject to the rights of holders of any outstanding preferred stock, the number of authorized shares of common stock or preferred stock may be increased or decreased by the affirmative vote of the holders of a majority of the shares entitled to vote on such matters, but in no instance can the number of authorized shares be reduced below the number of shares then outstanding. Common stock The certificate of incorporation of the Company provides for two classes of common stock, and for the conversion of each class into the other, to provide a mechanism by which holders of Class A common stock of the Company who may be limited in the amount of voting common stock of the Company they can hold pursuant to federal, state or foreign bank laws, to convert their shares into non-voting Class B common stock to prevent being in violation of such laws. Each holder of Class A common stock is entitled to one vote per share in connection with the election of directors and on all other matters submitted to a stockholder vote, provided, however, that, except as otherwise required by law, holders of Class A common stock are not entitled to vote on any amendment to the Company's amended and restated certificate of incorporation that relates solely to the terms of one or more outstanding series of the Company's preferred stock, if holders of the preferred stock series are entitled to vote on the amendment under the Company's certificate of incorporation or Delaware law. No holder of Class A common stock may accumulate votes in voting for directors of the Company. Each holder of Class B common stock is not entitled to vote except as otherwise provided by law, provided however that the Company must obtain the consent of a majority of the holders of Class B common stock to effect any amendment, alteration or repeal of any provision of the Company's amended and restated certificate of incorporation or amended and restated by-laws that would adversely affect the voting powers, preferences or rights of holders of Class B common stock. Except as otherwise provided by law, Class B common stock shares will not be counted as shares held by stockholders for purposes of determining whether a vote or consent has been approved or given by the requisite percentage of shares. Each share of Class A common stock is convertible at the option of the holder and at no cost into one share of Class B common stock, and each share of Class B common stock is convertible at the option of the holder and at no cost into one share of Class A common stock. The conversion ratios will be adjusted proportionally to reflect any stock split, stock dividend, merger, reorganization, recapitalization or other change in the Class A common stock and Class B common stock. Upon conversion, converted shares resume the status of authorized and unissued shares. Subject to the preferences of the holders of any of the Company's preferred stock that may be outstanding from time to time, each share of Class A common stock and Class B common stock will have an equal and ratable right to receive dividends and other distributions in cash, property or shares of stock as may be declared by the Company's board of directors out of assets or funds legally available for the payment of dividends and other distributions. In the event of the liquidation, dissolution or winding up of the Company, subject to the preferences of the holders of any preferred stock of the Company that may be outstanding from time to time, holders of Class A common stock and Class B common stock will be entitled to share equally and ratably in the assets available for distribution to the Company's stockholders. There are no redemption or sinking fund provisions applicable to the Class A or the Class B common stock. Preferred stock The Company's amended and restated certificate of incorporation permits the Company to issue up to 10,000,000 shares of preferred stock in one or more series with such designations, titles, voting powers, preferences and rights and such qualifications, limitations and restrictions as may be fixed by the board of directors of the Company without any further action by the Company's stockholders. The Company's board of directors may increase or decrease the number of shares of any series of preferred stock following the issuance of that series of preferred stock, but in no instance can the number of shares of a series of preferred stock be reduced below the number of shares of the series then outstanding. Preferred Stock and Purchase of Capped Call Option On May 19, 2015, the Company completed its offering of 120,750 shares of the Company's 5.625% Series A cumulative perpetual convertible preferred stock ("Series A Convertible Preferred Stock") that provided $117.2 million of proceeds, net of underwriting fees and issuance costs of $3.6 million . Each share of the Series A Convertible Preferred Stock is entitled to dividends at a rate of 5.625% per annum which will be payable, when and if declared by the board of directors of the Company, quarterly, in arrears, on February 15, May 15, August 15 and November 15 of each year. The Company may, at its option, pay dividends in cash, common stock or a combination thereof . The Company declared and accrued a cash dividend of $6.8 million , $6.8 million and $4.1 million for the years ended December 31, 2017 , 2016, and 2015 respectively. Each share of Series A Convertible Preferred Stock is non-voting and has a liquidity preference over the Company's Class A common stock and ranks senior to all classes or series of the Company's Class A common stock, but junior to all of the Company's existing and future indebtedness with respect to divided rights and rights upon the Company's involuntary liquidation, dissolution or winding down. Each share of Series A Convertible Preferred Stock is convertible, at the option of the holder, into a number of shares of our Class A common stock equal to the liquidation preference of $1,000 divided by the conversion rate. The initial conversion rate (subsequent to the December 5, 2016 reverse stock split) is 38.0619 shares (which equates to $26.27 per share) of the Company's Class A common stock for each share of the Series A Convertible Preferred Stock. At any time on or after May 20, 2020, the Company may elect to convert all outstanding shares of the Series A Convertible Preferred Stock into shares of the Company’s Class A common stock, cash or a combination thereof, at the Company’s election, in each case, based on the then-applicable conversion rate, if the last reported sale price of the Company’s Class A common stock equals or exceeds 150% of the then-current conversion price on at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days (including on the last trading day of such period) immediately prior to such election. At the time of conversion, the conversion rate may be adjusted based on certain events including but not limited to the issuance of cash dividends or Class A common stock as a dividends to the Company's Class A common shareholders or a share split or combination. In connection with the issuance and sale of the Series A Convertible Preferred Stock, the Company entered into a capped call option transaction (the “Capped Call Option Transaction”) with Nomura Global Financial Products Inc. (the “option counterparty”) for $15.9 million . The Capped Call Option Transaction is expected generally to reduce the potential dilution to the Company’s Class A common stock (if the Company elects to convert to common shares) and/or offset any cash payments that the Company is required to make upon conversion of any Series A Convertible Preferred Stock. The Capped Call Option Transaction has an initial effective strike price of $26.27 per share, which matches the initial conversion price of the Series A Convertible Preferred Stock, and a cap price of $33.54 per share. However, to the extent that the market price of Class A common stock, as measured under the terms of the Capped Call Option Transaction, exceeds the cap price thereof, there would nevertheless be dilution and/or such cash payments would not be offset. As the Capped Call Option Transaction is a free standing derivative that is indexed to the Company's own stock price and the Company controls if it is settled in cash or stock it qualifies for equity classification as a reduction to additional paid in capital. Treasury Stock Treasury stock of $186.8 million as of December 31, 2017 , compared to $153.8 million as of December 31, 2016 , resulted from $11.9 million acquired through repurchases of shares to cover employee minimum tax withholding obligations related to stock compensation vesting events under the Company's Equity Plan or other similar transactions, $1.6 million received from an escrow account established to satisfy the Company’s indemnification claims arising under the terms of the purchase agreement entered into in connection with the Company’s acquisition of Convergex Group, LLC and $19.5 million purchased in connection with a share repurchase program. The following represents the activity relating to the treasury stock held by the Company during the year ended December 31, 2017 : Treasury stock shares Cost Average cost per share Balance outstanding at December 31, 2016 9,810,802 $ 153,845 $ 15.68 Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions 822,996 11,889 14.45 Shares of stock received in respect of indemnification claims 97,612 1,626 16.66 Purchase of treasury stock 1,401,866 19,486 13.90 Balance outstanding at December 31, 2017 12,133,276 $ 186,846 $ 15.40

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income / (Loss) [Abstract]
Accumulated other comprehensive income (loss)	Accumulated Other Comprehensive Income (Loss) Accumulated other comprehensive income includes the after tax change in unrealized gains and losses on foreign currency translation adjustments. During the periods presented, the Company did not have material reclassifications out of other comprehensive income. Year Ended December 31, 2017 2016 2015 (dollars in thousands) Beginning Balance $ (2 ) $ — $ 17 Foreign currency translation (6 ) (2 ) (17 ) Ending Balance $ (8 ) $ (2 ) $ —

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The Company calculates its basic and diluted earnings per share in accordance with US GAAP. Basic earnings per share is calculated by dividing net income attributable to the Company's common stockholders by the weighted average number of common shares outstanding for the period. As of December 31, 2017 , there were 29,632,020 of Class A common shares outstanding. The Company has included 191,962 fully vested, unissued restricted stock units in its calculation of basic earnings per share. As of December 5, 2016, share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split. Diluted earnings per common share are calculated by adjusting the weighted average outstanding shares to assume conversion of all potentially dilutive items. The Company uses the treasury stock method to reflect the potential dilutive effect of the warrants (see Note 6 (a)), unexercised stock options, unvested restricted shares, restricted stock units, and SAR's. In calculating the number of dilutive shares outstanding, the shares of common stock underlying unvested restricted shares and restricted stock units are assumed to have been delivered, and options and warrants are assumed to have been exercised, for the entire period being presented. The assumed proceeds from the assumed vesting, delivery and exercising were calculated as the amount of compensation cost attributed to future services and not yet recognized. The Company can elect to settle the Series A Convertible Preferred Stock in shares, cash, or a combination of both. The Company's intent is to settle in cash and, based on current and projected liquidity needs, the Company has the ability to do so. The computation of earnings per share is as follows: Year Ended December 31, 2017 2016 2015 (dollars in thousands, except share and per share data) Net income (loss) $ (37,091 ) $ (12,395 ) $ 58,975 Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds 23,791 6,882 15,246 Net income (loss) attributable to Cowen Inc. (60,882 ) (19,277 ) 43,729 Preferred stock dividends 6,792 6,792 4,075 Net income (loss) attributable to Cowen Inc. common stockholders $ (67,674 ) $ (26,069 ) $ 39,654 Shares for basic and diluted calculations: Weighted average shares used in basic computation 29,492 26,857 27,522 Stock options — — 3 Performance based restricted stock — — 65 Stock appreciation rights — — 35 Restricted stock — — 1,418 Weighted average shares used in diluted computation 29,492 26,857 29,043 Earnings (loss) per share: Basic $ (2.29 ) $ (0.97 ) $ 1.44 Diluted $ (2.29 ) $ (0.97 ) $ 1.37

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting The Company conducts its operations through two segments: the investment management segment and the broker‑dealer segment. These activities are conducted primarily in the United States and substantially all of its revenues are generated domestically. The performance measure for these segments is Economic Income (Loss), which management uses to evaluate the financial performance of and make operating decisions for the segments including determining appropriate compensation levels. Expenses not directly associated with specific segments are allocated based on the most relevant measures applicable, including headcount, square footage and other factors. In general, Economic Income (Loss) is a pre-tax measure that (i) eliminates the impact of consolidation for consolidated funds and excludes (ii) goodwill and intangible impairment (iii) certain other transaction-related adjustments and/or reorganization expenses (iv) the bargain purchase gain which resulted from the Convergex Group acquisition (v) certain costs associated with debt and (vi) preferred stock dividends. In addition, Economic Income (Loss) revenues include investment income that represents the income the Company has earned in investing its own capital, including realized and unrealized gains and losses, interest and dividends, net of associated investment related expenses. For US GAAP purposes, these items are included in each of their respective line items. Economic Income (Loss) revenues also include management fees, incentive income and investment income earned through the Company's investment as a general partner in certain real estate entities and the Company's investment in the activist business. For US GAAP purposes, all of these items are recorded in other income (loss). In addition, Economic Income (Loss) expenses are reduced by reimbursement from affiliates, which for US GAAP purposes is presented gross as part of revenue. As further stated below, one major difference between Economic Income (Loss) and US GAAP net income (loss) is that Economic Income (Loss) presents the segments' results of operations without the impact resulting from the full consolidation of any of the Consolidated Funds. The consolidation of these funds results include the pro rata share of the income or loss attributable to other owners of such entities which is reflected in net income (loss) attributable to redeemable non-controlling interest in consolidated subsidiaries in the accompanying consolidated statements of operations. This pro rata share has no effect on the overall financial performance for the investment management segment, as ultimately, this income or loss is not income or loss for the investment management segment itself. Included in Economic Income (Loss) is the actual pro rata share of the income or loss attributable to the Company as an investor in such entities, which is relevant in management making operating decisions and evaluating financial performance. The following tables set forth operating results for the Company's investment management and broker-dealer segments and related adjustments necessary to reconcile the Company's Economic Income (Loss) measure to arrive at the Company's consolidated US GAAP net income (loss): Year Ended December 31, 2017 Adjustments Investment Broker-Dealer Total Economic Income/(Loss) Funds Consolidation Other Adjustments US GAAP (dollars in thousands) Revenues Investment banking $ — $ 223,614 $ 223,614 $ — $ — $ 223,614 Brokerage 38 312,742 312,780 — (19,170 ) (i) 293,610 Management fees 52,239 3,148 55,387 (2,593 ) (19,549 ) (a) 33,245 Incentive income (loss) 26,028 — 26,028 (1,739 ) (18,906 ) (a) 5,383 Investment income (loss) 31,447 13,695 45,142 — (45,142 ) (c)(f) — Interest and dividends — — — — 49,440 (c) 49,440 Reimbursement from affiliates — — — (297 ) 3,157 (e) 2,860 Aircraft lease revenue — — — — 3,751 (f) 3,751 Reinsurance premiums — — — — 30,996 (g) 30,996 Other revenue 1,575 1,656 3,231 — 5,330 (g) 8,561 Consolidated Funds revenues — — — 7,321 — 7,321 Total revenues 111,327 554,855 666,182 2,692 (10,093 ) 658,781 Expenses Non interest expense 92,567 532,820 625,387 (199 ) 58,935 (b)(d) 684,123 Interest and dividends 14,268 4,620 18,888 — 42,061 (c) 60,949 Consolidated Funds expenses — — — 12,526 — 12,526 Total expenses 106,835 537,440 644,275 12,327 100,996 757,598 Total other income (loss) — — — 31,073 74,706 (c) (h) (j) 105,779 Income taxes expense / (benefit) — — — — 44,053 (b) 44,053 (Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (6,072 ) — (6,072 ) (21,438 ) 3,719 (23,791 ) Economic Income (Loss) / Net Income (loss) attributable to Cowen Inc. $ (1,580 ) $ 17,415 $ 15,835 $ — $ (76,717 ) $ (60,882 ) Year Ended December 31, 2016 Adjustments Investment Broker-Dealer Total Economic Income/(Loss) Funds Consolidation Other Adjustments US GAAP (dollars in thousands) Revenues Investment banking $ — $ 133,279 $ 133,279 $ — $ — $ 133,279 Brokerage — 207,040 207,040 — (7,860 ) (i) 199,180 Management fees 64,086 3,162 67,248 (1,665 ) (24,971 ) (a) 40,612 Incentive income (loss) 26,274 — 26,274 (714 ) (17,226 ) (a) 8,334 Investment income (loss) 3,015 1,008 4,023 — (4,023 ) (c)(f) — Interest and dividends — — — — 14,732 (c) 14,732 Reimbursement from affiliates — — — (303 ) 10,807 (e) 10,504 Aircraft lease revenue — — — — 4,161 (f) 4,161 Reinsurance premiums — — — — 32,459 (g) 32,459 Other revenue 29,202 565 29,767 — (7,412 ) (g) 22,355 Consolidated Funds revenues — — — 5,949 — 5,949 Total revenues 122,577 345,054 467,631 3,267 667 471,565 Expenses Non interest expense 102,163 369,188 471,351 (429 ) 37,824 (b)(d) 508,746 Interest and dividends 12,827 4,363 17,190 — 12,118 (c) 29,308 Consolidated Funds expenses — — — 9,064 — 9,064 Total expenses 114,990 373,551 488,541 8,635 49,942 547,118 Total other income (loss) — — — 8,532 35,534 (c) 44,066 Income taxes expense / (benefit) — — — — (19,092 ) (b) (19,092 ) (Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (7,821 ) — (7,821 ) (3,164 ) 4,103 (6,882 ) Economic Income (Loss) / Net Income (loss) attributable to Cowen Inc. $ (234 ) $ (28,497 ) $ (28,731 ) $ — $ 9,454 $ (19,277 ) Year Ended December 31, 2015 Adjustments Alternative Investment Broker-Dealer Total Economic Income/(Loss) Funds Consolidation Other Adjustments US GAAP (dollars in thousands) Revenues Investment banking $ — $ 222,781 $ 222,781 $ — $ — $ 222,781 Brokerage — 160,436 160,436 — (2,714 ) 157,722 Management fees 68,989 1,026 70,015 (1,307 ) (26,802 ) (a) 41,906 Incentive income (loss) (1,544 ) — (1,544 ) (736 ) 3,746 (a) 1,466 Investment income (loss) 49,244 13,352 62,596 — (62,596 ) (c) — Interest and dividends — — — — 13,796 (c) 13,796 Reimbursement from affiliates — — — (190 ) 21,747 (e) 21,557 Other revenue 14,492 890 15,382 — (11,656 ) (c) 3,726 Consolidated Funds revenues — — — 1,613 — 1,613 Total revenues 131,181 398,485 529,666 (620 ) (64,479 ) 464,567 Expenses Non interest expense 107,291 362,463 469,754 — 6,090 (b)(c)(d) 475,844 Interest and dividends 11,839 4,745 16,584 — 9,636 (c) 26,220 Consolidated Funds expenses — — — 2,310 — 2,310 Total expenses 119,130 367,208 486,338 2,310 15,726 504,374 Total other income (loss) — — — 8,781 42,505 (c) 51,286 Income taxes expense / (benefit) — — — — (47,496 ) (b) (47,496 ) (Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (8,796 ) — (8,796 ) (5,851 ) (599 ) (15,246 ) Economic Income (Loss) / Net Income (loss) attributable to Cowen Inc. $ 3,255 $ 31,277 $ 34,532 $ — $ 9,197 $ 43,729 The following is a summary of the adjustments made to US GAAP net income (loss) for the segment to arrive at Economic Income (Loss): Funds Consolidation: The impacts of consolidation and the related elimination entries of the Consolidated Funds are not included in Economic Income (Loss). Adjustments to reconcile to US GAAP net income (loss) included elimination of incentive income and management fees earned from the Consolidated Funds and addition of fund expenses excluding management fees paid, fund revenues and investment income (loss). Other Adjustments: (a) Economic Income (Loss) recognizes revenues (i) net of distribution fees paid to agents and (ii) our proportionate share of management and incentive fees of certain real estate operating entities, the healthcare royalty business and the activist business. (b) Economic Income (Loss) excludes income taxes and acquisition related adjustments as management does not consider these items when evaluating the performance of the segment. (c) Economic Income (Loss) recognizes Company income from proprietary trading (including interest and dividends). (d) Economic Income (Loss) recognizes the Company's proportionate share of expenses, for certain real estate operating entities and the activist business, for which the investments are recorded under the equity method of accounting for investments. (e) Reimbursement from affiliates is shown as a reduction of Economic Income expenses, but is included as a part of revenues under US GAAP. (f) Aircraft lease revenue is shown net of expenses in investment income for Economic Income (Loss). (g) Economic Income (Loss) recognizes underwriting income from the Company's insurance related activities, net of expenses, within other revenue. (h) Economic Income (Loss) excludes the bargain purchase gain which resulted from the Convergex Group acquisition. (i) Economic Income (Loss) brokerage revenues included net securities borrowed and securities loaned activities. (j) Economic Income (Loss) excludes gain / (loss) on debt extinguishment. For the year ended December 31, 2017 and 2016 , there was no one fund or other customer which represented more than 10% of the Company's total revenues.

Regulatory Requirements

Regulatory Requirements	12 Months Ended
	Dec. 31, 2017
Brokers and Dealers [Abstract]
Regulatory Requirements	Regulatory Requirements As registered broker-dealers, Cowen and Company, Cowen Execution, ATM Execution, Cowen Prime and Westminster are subject to the SEC's Uniform Net Capital Rule 15c3-1 (the “Rule”), which requires the maintenance of minimum net capital. Each registered broker-dealer has elected to compute net capital under the alternative method permitted by the Rule. Under the alternative method Cowen and Company's minimum net capital requirement, as defined in (a)(4) of the Rule, is $1.0 million . Cowen Execution, ATM Execution, Cowen Prime and Westminster are required to maintain minimum net capital, as defined in (a)(1)(ii) of the Rule, equal to the greater of $250,000 or 2% of aggregate debits arising from customer transactions. Advances to affiliates, repayment of borrowings, distributions, dividend payments and other equity withdrawals are subject to certain notification and other requirements of the Rule and other regulatory bodies. Cowen Execution is also subject to Commodity Futures Trading Commission Regulation 1.17 (“Regulation 1.17”) and Options Clearing Corporation (“OCC”) Rule 302. Regulation 1.17 requires Cowen Execution to maintain net capital equal to or in excess of $45,000 or the amount of net capital required by Rule 15c3-1, whichever is greater. OCC Rule 302 requires maintenance of net capital equal to the greater of $2,000,000 or 2% of aggregate debit items. At December 31, 2017 , the Company had $108.7 million of net capital in excess of this minimum requirement. Ramius UK, Cowen International Ltd and Cowen Execution Ltd are subject to the capital requirements of the FCA of the U.K. Financial Resources, as defined, must exceed the requirement of the FCA . As of December 31, 2017 , these regulated broker-dealers had regulatory net capital or financial resources, regulatory net capital requirements or minimum FCA requirement and excess as follows : Subsidiary Net Capital Minimum Net Capital Requirement Excess Net Capital (dollars in millions) Cowen and Company $ 40.2 $ 1.0 $ 39.2 Cowen Execution $ 111.4 $ 2.7 $ 108.7 ATM Execution $ 1.0 $ 0.3 $ 0.7 Cowen Prime $ 12.3 $ 0.3 $ 12.0 Westminster $ 7.6 $ 0.3 $ 7.3 Ramius UK $ 0.2 $ 0.1 $ 0.1 Cowen International Ltd $ 11.5 $ 7.1 $ 4.4 Cowen Execution Ltd $ 3.8 $ 2.6 $ 1.2 Cowen and Company, Cowen Prime and ATM Execution claim exemption from SEC Rule 15c3-3 subparagraph (k)(2)(ii) of the Securities Exchange Act of 1934 since they clear their securities transactions on a fully disclosed basis and promptly transmits all customer funds and securities to the clearing broker-dealer that carries the accounts. Cowen and Company, Cowen Prime and Westminster claim exemption from SEC Rule 15c3-3 subparagraph (k)(2)(i) of the Securities Exchange Act of 1934 since they conduct primarily all financial transactions with their customers through a bank account designated as Special Account for the Exclusive Benefit of Customers. In accordance with the requirements of SEC Rule 15c3-3, Cowen Execution may be required to deposit in a Special Reserve Account, cash or acceptable qualified securities for the exclusive benefit of customers. As of December 31, 2017, Cowen Execution had segregated approximately $20.3 million of cash, while its required deposit was $10.5 million . As a clearing broker-dealer, Cowen Execution is required to compute a reserve requirement for proprietary accounts of broker-dealers (“PAB”), as defined in SEC Rule 15c3-3. PAB calculation is completed to allow each correspondent firm that uses Cowen Execution as its clearing broker-dealer to classify its assets held by Cowen Execution as allowable assets in the correspondent's net capital calculation. At December 31, 2017, Cowen Execution had $29.7 million of cash on deposit in special reserve bank accounts for PAB, which was in excess of its required deposit of $17.1 million . PAB held at external clearing brokers are considered allowable assets for net capital purposes, pursuant to agreements between Cowen and Company, ATM Execution, Cowen Prime, and their clearing brokers, which require, among other things, that those clearing brokers perform computations for PAB and segregate certain balances on behalf of Cowen and Company, ATM Execution and Cowen Prime, if applicable. Cowen’s Luxembourg reinsurance companies, Vianden RCG Re SCA (“Vianden”) and Hollenfels, are required to maintain a solvency capital ratio as calculated by relevant European Commission directives and local regulatory rules in Luxembourg. Each company’s solvency capital ratio as of December 31, 2017 was in excess of this minimum requirement. Based on minimum capital and surplus requirements pursuant to the laws of the state of New York that apply to captive insurance companies, RCG Insurance Company, Cowen’s captive insurance company incorporated and licensed in the state of New York, was required to maintain capital and surplus of approximately $0.3 million as of December 31, 2017 . RCG Insurance Company’s capital and surplus as of December 31, 2017 totaled approximately $28.7 million .

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The Company and its affiliated entities are the managing member, general partner and/or investment manager to the Company's investment management products and certain managed accounts. Management fees and incentive income are primarily earned from affiliated entities. As of December 31, 2017 and 2016 , $13.5 million and $12.6 million , respectively, included in fees receivable are earned from related parties. The Company may, at its discretion, reimburse certain fees charged to the funds that it manages to avoid duplication of fees when such funds have an underlying investment in another affiliated investment fund. For the years ended December 31, 2017 and 2016, the Company reimbursed the funds it manages $0.1 million and $0.2 million , respectively, which were recorded net in management fees and incentive income in the accompanying consolidated statements of operation. For the year ended December 31, 2015, these amounts were immaterial. As of December 31, 2017 , related amounts still payable were immaterial. As of December 31, 2016 , related amounts still payable were $0.3 million and were reflected in fees payable in the accompanying consolidated statements of financial condition. Fees receivable and fees payable are recorded at carrying value, which approximates fair value. The Company may also make loans to employees or other affiliates, excluding executive officers of the Company. These loans are interest bearing and settle pursuant to the agreed-upon terms with such employees or affiliates and are included in due from related parties in the accompanying consolidated statements of financial condition. As of December 31, 2017 and 2016 , loans to employees of $11.1 million and $9.2 million , respectively, were included in due from related parties on the accompanying consolidated statements of financial condition. Of these amounts $4.8 million and $3.3 million , respectively, are related to forgivable loans. These forgivable loans provide for a cash payment up-front to employees, with the amount due back to the Company forgiven over a vesting period. An employee that voluntarily ceases employment, or is terminated with cause, is generally required to pay back to the Company any unvested forgivable loans granted to them. The forgivable loans are recorded as an asset to the Company on the date of grant and payment, and then amortized to compensation expense on a straight-line basis over the vesting period. The vesting period on forgivable loans is generally one to three years. The Company recorded compensation expense of $2.1 million , $1.2 million , and $3.2 million for the years ended December 31, 2017 , 2016 , and 2015 respectively. This expense is included in employee compensation and benefits in the accompanying consolidated statement of operations. For the year ended December 31, 2017 , the interest income was $0.1 million and for the years ended December 2016 and 2015, the interest income was insignificant for these related party loans and advances. This income is included in interest and dividends in the accompanying consolidated statement of operations. Included in due to related parties is approximately $0.6 million and $0.7 million as of December 31, 2017 and 2016 , respectively, related to a subordination agreement with an investor in certain real estate funds. This total is based on a hypothetical liquidation of the real estate funds as of the balance sheet date. As of December 31, 2017 and 2016 , included in due from related parties is $14.0 million and $18.7 million , respectively, related to the sales of portions of the Company's ownership interest in the activist business of Starboard Value to the Starboard principals. It is being financed through the profits of the relevant Starboard entities over a 5 year period and earns interest at 5% per annum. The interest income for the years ended December 31, 2017 and 2016, was $0.8 million and $0.6 million , respectively. The interest income for the year ended December 31, 2015 was immaterial. The remaining balance included in due from related parties of $9.7 million and $11.8 million as of December 31, 2017 and 2016 , respectively, relates to amounts due to the Company from affiliated funds and real estate entities due to expenses paid on their behalf. Employees and certain other related parties invest on a discretionary basis within consolidated entities. These investments generally are subject to preferential management fee and performance fee arrangements. As of December 31, 2017 and 2016 , such investments aggregated $ 28.2 million and $ 32.9 million , respectively, were included in redeemable non-controlling interests on the accompanying consolidated statements of financial condition. Their share of the net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds aggregated $ 7.2 million , $ 5.7 million , and $10.4 million for the years ended December 31, 2017 , 2016 , and 2015, respectively.

Guarantees and Off-Balance Shee

Guarantees and Off-Balance Sheet Arrangements	12 Months Ended
	Dec. 31, 2017
Guarantees and Off Balance Sheet Arrangements [Abstract]
Guarantees and Off-Balance Sheet Arrangements	Guarantees and Off-Balance Sheet Arrangements Guarantees US GAAP requires the Company to disclose information about its obligations under certain guarantee arrangements. Those standards define guarantees as contracts and indemnification agreements that contingently require a guarantor to make payments to the guaranteed party based on changes in an underlying security (such as an interest or foreign exchange rate, security or commodity price, an index or the occurrence or nonoccurrence of a specified event) related to an asset, liability or equity security of a guaranteed party. Those standards also define guarantees as contracts that contingently require the guarantor to make payments to the guaranteed party based on another entity's failure to perform under an agreement as well as indirect guarantees of the indebtedness of others. In the normal course of its operations, the Company enters into contracts that contain a variety of representations and warranties which provide general indemnifications. The Company's maximum exposure under these arrangements is unknown as this would involve future claims that may be made against the Company that have not yet occurred. However, based on experience, the Company expects the risk of loss to be remote. The Company indemnifies and guarantees certain service providers, such as clearing and custody agents, trustees and administrators, against specified potential losses in connection with their acting as an agent of, or providing services to, the Company or its affiliates. The Company also indemnifies some clients against potential losses incurred in the event specified third-party service providers, including sub-custodians and third-party brokers, improperly execute transactions. The maximum potential amount of future payments that the Company could be required to make under these indemnifications cannot be estimated. However, the Company believes that it is unlikely it will have to make significant payments under these arrangements and has not recorded any contingent liability in the consolidated financial statements for these indemnifications. The Company also provides representations and warranties to counterparties in connection with a variety of commercial transactions and occasionally indemnifies them against potential losses caused by the breach of those representations and warranties. The Company may also provide standard indemnifications to some counterparties to protect them in the event additional taxes are owed or payments are withheld, due either to a change in or adverse application of certain tax laws. These indemnifications generally are standard contractual terms and are entered into in the normal course of business. The maximum potential amount of future payments that the Company could be required to make under these indemnifications cannot be estimated. However, the Company believes it is unlikely it will have to make material payments under these arrangements and has not recorded any contingent liability in the accompanying consolidated financial statements for these indemnifications. The Company may maintain cash and cash equivalents at financial institutions in excess of federally insured limits. The Company has not experienced any material losses in such accounts and does not believe it is exposed to significant credit risks in relation to such accounts. Off-Balance Sheet Arrangements The Company has no material off-balance sheet arrangements, which have not been disclosed, as of December 31, 2017 and 2016 . Through indemnification provisions in the clearing agreement, customer activities may expose the Company to off-balance-sheet credit risk. Pursuant to the clearing agreement, the Company is required to reimburse the Company's clearing broker, without limit, for any losses incurred due to a counterparty's failure to satisfy its contractual obligations. However, these transactions are collateralized by the underlying security, thereby reducing the associated risk to changes in the market value of the security through the settlement date. The Company’s customer securities activities are transacted on a delivery versus payment, cash or margin basis. In delivery versus payment transactions, the Company is exposed to risk of loss in the event of the customers’ or brokers’ inability to meet the terms of their contracts. In margin transactions, the Company extends credit to clients collateralized by cash and securities in their account. In the event the customers or brokers fail to satisfy their obligations, the Company may be required to purchase or sell securities at prevailing market prices in order to fulfill the obligations. The Company’s exposure to credit risk can be directly impacted by volatile securities markets, which may impair the ability of counterparties to satisfy their contractual obligations. The Company seeks to control its credit risk through a variety of reporting and control procedures, including establishing credit limits based upon a review of the customers’ financial condition and credit ratings. The Company seeks to control the risk associated with its customer margin transactions by requiring customers to maintain margin collateral in compliance with various regulatory and internal guidelines. The Company also monitors required margin levels daily and, pursuant to its guidelines, requires customers to deposit additional collateral, or reduce positions, when necessary. In addition, during the normal course of business, the Company has exposure to a number of risks including market risk, currency risk, credit risk, operational risk, liquidity risk and legal risk. As part of the Company's risk management process, these risks are monitored on a regular basis throughout the course of the year. The Company enters into secured and unsecured borrowing agreements to obtain funding necessary to cover daily securities settlements with clearing corporations. Funding is required for unsettled customer delivery versus payment and riskless principal transaction, as well as to meet deposit requirements with clearing organizations. Secured arrangements are collateralized by the unsettled customer securities. The Company maintains uncommitted financing arrangements with large financial institutions, the details of which are summarized below as of December 31, 2017 . Lender Contractual Amount Available Amount Maturity Date Description Pledge Lines (dollars in thousands) BMO Harris Bank $ 150,000 $ 150,000 None Secured DTC Pledge Line Total 150,000 150,000 Revolving Credit Facility BMO Harris Bank 30,000 30,000 August 2, 2018 Unsecured liquidity facility to cover increases in NSCC margin deposit requirements Total Credit Lines $ 180,000 $ 180,000

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On February 13, 2018, the Company's Board of Directors approved a $23.6 million increase in the Company's share repurchase program (see Note 24) bringing the total remaining shares available for repurchase to $25.0 million . The Company has evaluated events that have occurred after the balance sheet date but before the financial statements are issued and has determined that there were no other subsequent events requiring adjustment or disclosure in the consolidated financial statements.

Supplemental Financial Informat

Supplemental Financial Information	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Supplemental Financial Information	Supplemental Financial Information The following table presents unaudited quarterly results of operations for 2017 and 2016 . These quarterly results reflect all normal recurring adjustments that are, in the opinion of management, necessary for a fair presentation of the results. Revenues and net income (loss) can vary significantly from quarter to quarter due to the nature of the Company's business activities. Cowen Inc. Quarterly Financial Information (Unaudited) Quarter Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 (dollars in thousands, except per share data) Total revenues $ 114,971 $ 160,530 $ 178,830 $ 204,450 Income (loss) before income taxes 14,000 27,800 12,109 (46,947 ) Income tax expense (benefit) 1,911 (785 ) 2,281 40,646 Net income (loss) from continuing operations 12,089 28,585 9,828 (87,593 ) Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds 9,105 21,145 5,162 (11,621 ) Net income (loss) attributable to Cowen Inc. 2,984 7,440 4,666 (75,972 ) Preferred stock dividends 1,698 1,698 1,698 1,698 Net income (loss) attributable to Cowen Inc. common stockholders $ 1,286 $ 5,742 $ 2,968 $ (77,670 ) Earnings (loss) per share: Basic $ 0.05 $ 0.20 $ 0.09 $ (2.51 ) Diluted $ 0.05 $ 0.19 $ 0.09 $ (2.51 ) Weighted average number of common shares: Basic 27,061 28,634 31,271 30,934 Diluted 28,401 29,474 32,246 30,934 Quarter Ended March 31, 2016 June 30, 2016 September 30, 2016 December 31, 2016 (dollars in thousands, except per share data) Total revenues $ 101,039 $ 117,231 $ 131,027 $ 122,268 Income (loss) before income taxes (11,315 ) (39,153 ) 24,018 (5,037 ) Income tax expense (benefit) (3,320 ) (11,992 ) 8,759 (12,539 ) Net income (loss) from continuing operations (7,995 ) (27,161 ) 15,259 7,502 Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (4,297 ) (16,705 ) 18,478 9,406 Net income (loss) attributable to Cowen Inc. (3,698 ) (10,456 ) (3,219 ) (1,904 ) Preferred stock dividends 1,698 1,698 1,698 1,698 Net income (loss) attributable to Cowen Inc. common stockholders $ (5,396 ) $ (12,154 ) $ (4,917 ) $ (3,602 ) Earnings (loss) per share: Basic (a) $ (0.20 ) $ (0.45 ) $ (0.18 ) $ (0.13 ) Diluted (a) $ (0.20 ) $ (0.45 ) $ (0.18 ) $ (0.13 ) Weighted average number of common shares: Basic (a) 26,591 26,867 26,993 26,973 Diluted (a) 26,591 26,867 26,993 26,973 (a) Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.

Significant Accounting Polici40

Significant Accounting Policies - Annual (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of presentation	Basis of Presentation These consolidated financial statements are prepared in accordance with US GAAP as promulgated by the Financial Accounting Standards Board ("FASB") through the Accounting Standards Codification as the source of authoritative accounting principles in the preparation of financial statements, and include the accounts of the Company, its operating and other subsidiaries, and entities in which the Company has a controlling financial interest or a general partner interest. All material intercompany transactions and balances have been eliminated on consolidation. Certain fund entities that are consolidated in these accompanying consolidated financial statements, as further discussed below, are not subject to the consolidation provisions with respect to their own controlled investments pursuant to their specialized accounting. The Company serves as the managing member/general partner and/or investment manager to affiliated fund entities which it sponsors and manages. Funds in which the Company has a controlling financial interest are consolidated with the Company pursuant to US GAAP as described below. Consequently, the Company's consolidated financial statements reflect the assets, liabilities, income and expenses of these funds on a gross basis. The ownership interests in these funds that are not owned by the Company are reflected as redeemable non-controlling interests in consolidated subsidiaries in the accompanying consolidated financial statements. The management fees and incentive income earned by the Company from these funds are eliminated in consolidation. Certain reclassifications have been made to prior period amounts in order to conform to current period presentation.
Principles of consolidation	Principles of consolidation The Company consolidates all entities that it controls through a majority voting interest or otherwise, including those funds in which the Company either directly or indirectly has a controlling financial interest. In addition, the Company consolidates all variable interest entities for which it is the primary beneficiary. In accordance with these standards, during the twelve months ended December 31, 2017 the Company consolidated seven funds for which it acts (or acted) as the general partner and investment manager. As of December 31, 2017 the Company consolidated the following funds: Ramius Enterprise LP (“Enterprise LP”), Ramius Merger Fund LLC (the "Merger Fund"), Cowen Private Investments LP ("Cowen Private"), Cowen Healthcare Investments Fund II LP ("Cowen Healthcare II"), Caerus Select Fund LP ("Caerus LP") (between May 1, 2016 through March 1, 2017 when the fund was liquidated), Ramius Archview Credit and Distressed Master Fund ("Archview Master Fund") (from December 31, 2015 through July 31, 2017 when the fund was liquidated) and Ramius Merger Arbitrage UCITS Fund ("UCITS Fund") (collectively the "Consolidated Funds"). The Company determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting operating entity ("VOE") or a variable interest entity ("VIE") under US GAAP. Voting Operating Entities — VOEs are entities in which (i) the total equity investment at risk is sufficient to enable the entity to finance its activities independently and (ii) the equity holders at risk have the obligation to absorb losses, the right to receive residual returns and the right to direct the activities of the entity that most significantly impact the entity's economic performance. Under US GAAP, the usual condition for a controlling financial interest in a VOE is ownership of a majority voting interest. Accordingly, the Company consolidates all VOEs in which it owns a majority of the entity's voting shares or units. Variable Interest Entities— VIEs are entities that lack one or more of the characteristics of a VOE. In accordance with US GAAP, an enterprise must consolidate all VIEs of which it is the primary beneficiary. Under the US GAAP consolidation model for VIEs, an enterprise that (1) has the power to direct the activities of a VIE that most significantly impacts the VIE's economic performance, and (2) has an obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE, is considered to be the primary beneficiary of the VIE and thus is required to consolidate it. The Company reconsiders whether it is the primary beneficiary of a VIE by performing a periodic qualitative and/or quantitative analysis of the VIE that includes a review of, among other things, its capital structure, contractual agreements between the Company and the VIE, the economic interests that create or absorb variability, related party relationships and the design of the VIE. As of December 31, 2017 and 2016 , the total net assets of the consolidated VIEs were $482.8 million and $461.6 million , respectively. The VIEs act as investment managers and/or investment companies that may be managed by the Company or the Company may have equity interest in those investment companies. The VIEs are financed through their operations and/or loan agreements with the Company. As of December 31, 2017 the Company holds variable interests in Ramius Enterprise Master Fund Ltd (“Enterprise Master”) and Ramius Merger Master Fund Ltd ("Merger Master") (collectively the “Unconsolidated Master Funds”) through the Consolidated Funds. Investment companies, which account for their investments under the specialized industry accounting guidance for investment companies prescribed under US GAAP, are not subject to the consolidation provisions for their investments. Therefore, the Company has not consolidated the Unconsolidated Master Funds. In the ordinary course of business, the Company also sponsors various other entities that it has determined to be VIEs. These VIEs are primarily funds and real estate entities for which the Company serves as the general partner, managing member and/or investment manager with decision-making rights. The Company does not consolidate the Unconsolidated Master Funds or real estate entities that are VIEs as it has concluded that it is not the primary beneficiary in each instance. Fund investors are entitled to all of their economics of these VIEs with the exception of the management fee and incentive income, if any, earned by the Company. The Company's involvement with funds and real estate entities that are unconsolidated VIEs is limited to providing investment management services in exchange for management fees and incentive income. Although the Company may advance amounts and pay certain expenses on behalf of the funds and real estate entities that it considers to be VIEs, it does not provide, nor is it required to provide, any type of substantive financial support to these entities outside of regular investment management services (see Note 6 for additional disclosures on VIEs). Equity Method Investments — For operating entities over which the Company exercises significant influence but which do not meet the requirements for consolidation as outlined above, the Company uses the equity method of accounting. The Company's investments in equity method investees are recorded in other investments in the accompanying consolidated statements of financial condition. The Company's share of earnings or losses from equity method investees is included in net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that the carrying amounts of such investments may not be recoverable. The difference between the carrying value of the equity method investment and its estimated fair value is recognized as an impairment charge when the loss in value is deemed other than temporary. Other — If the Company does not consolidate an entity, apply the equity method of accounting or account for an investment under the cost method, the Company accounts for such entities (primarily, all securities of such entity which are bought and held principally for the purpose of selling them in the near term as trading securities) in accordance with US GAAP, at fair value with unrealized gains (losses) resulting from changes in fair value reflected within net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. Retention of Specialized Accounting — The Consolidated Funds and certain other consolidated companies are investment companies and apply specialized industry accounting for investment companies. The Company has retained this specialized accounting for these funds pursuant to US GAAP. The Company reports its investments on the consolidated statements of financial condition at their estimated fair value, with unrealized gains (losses) resulting from changes in fair value reflected within net realized and unrealized gains (losses) on investments and other transactions. Accordingly, the accompanying consolidated financial statements reflect different accounting policies for investments depending on whether or not they are held through a consolidated investment company. In addition, the Company's broker-dealer subsidiaries , Cowen and Company, LLC ("Cowen and Company"), Cowen Execution, Westminster, Cowen Execution Ltd, ATM Execution LLC ("ATM Execution"), Cowen International Limited ("Cowen International Ltd"), Ramius UK Ltd. ("Ramius UK") and Cowen Prime Services LLC ("Cowen Prime") apply the specialized industry accounting for brokers and dealers in securities also prescribed under US GAAP. The Company also retains specialized accounting upon consolidation.
Use of estimates	Use of estimates The preparation of the accompanying consolidated financial statements in conformity with US GAAP requires the management of the Company to make estimates and assumptions that affect the fair value of securities and other investments, the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the accompanying consolidated financial statements, the accounting for goodwill and identifiable intangible assets and the reported amounts of revenues and expenses during the reporting period. Actual results could materially differ from those estimates.
Cash and cash equivalents	Cash and cash equivalents The Company considers investments in money market funds and other highly liquid investments with original maturities of three months or less which are deposited with a bank or prime broker to be cash equivalents. Cash and cash equivalents held at Consolidated Funds, although not legally restricted, are not available to fund the general liquidity needs of the Company. The Company may also be exposed to credit risk as a result of cash being held at several banks.
Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block]	Allowance for doubtful accounts The allowance for doubtful accounts is based on the Company’s assessment of the collectability of receivables related to securities transactions, prepaid research and other receivables. The Company considers factors such as historical experience, credit quality, age of balances and current economic conditions that may affect collectability in determining the allowance for doubtful accounts. Specifically for prepaid research, the Company reviews clients' historical, current and forecasted trading activity in determining the allowance for doubtful accounts. Expense related to the allowance for doubtful accounts as well as any recoveries of amounts previously charged is reflected in other expenses in the accompanying consolidated statements of operations.
Valuation of investments and derivative contracts	Valuation of investments and derivative contracts US GAAP establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1 measurements) and the lowest priority to unobservable inputs (level 3 measurements). The three levels of the fair value hierarchy are as follows: Level 1 Inputs that reflect unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date; Level 2 Inputs other than quoted prices that are observable for the asset or liability either directly or indirectly, including inputs in markets that are not considered to be active; and Level 3 Fair value is determined based on pricing inputs that are unobservable and includes situations where there is little, if any, market activity for the asset or liability. The determination of fair value for assets and liabilities in this category requires significant management judgment or estimation. Inputs are used in applying the various valuation techniques and broadly refer to the assumptions that market participants use to make valuation decisions, including assumptions about risk. Inputs may include price information, volatility statistics, specific and broad credit data, liquidity statistics, and other factors. A financial instrument's level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. However, the determination of what constitutes “observable” requires significant judgment by the Company. The Company considers observable data to be that market data which is readily available, regularly distributed or updated, reliable and verifiable, not proprietary, and provided by independent sources that are actively involved in the relevant market. The categorization of a financial instrument within the hierarchy is based upon the pricing transparency of the instrument and does not necessarily correspond to the Company's perceived risk of that instrument. The Company and its operating subsidiaries act as the manager for the Consolidated Funds. Both the Company and the Consolidated Funds hold certain investments which are valued by the Company, acting as the investment manager. The fair value of these investments is generally estimated based on proprietary models developed by the Company, which include discounted cash flow analysis, public market comparables, and other techniques and may be based, at least in part, on independently sourced market information. The material estimates and assumptions used in these models include the timing and expected amount of cash flows, the appropriateness of discount rates used, and, in some cases, the ability to execute, timing of, and estimated proceeds from expected financings. Significant judgment and estimation goes into the selection of an appropriate valuation methodology as well as the assumptions used in these models, and the timing and actual values realized with respect to investments could be materially different from values derived based on the use of those estimates. The valuation methodologies applied impact the reported value of the Company's investments and the investments held by the Consolidated Funds in the consolidated financial statements. Certain of the Company's investments are relatively illiquid or thinly traded and may not be immediately liquidated on demand if needed. Fair values assigned to these investments may differ significantly from the fair values that would have been used had a ready market for the investments existed and such differences could be material . The Company primarily uses the “market approach” to value its financial instruments measured at fair value. In determining an instrument's level within the hierarchy, the Company categorizes the Company's financial instruments into three categories: securities, derivative contracts and other investments. To the extent applicable, each of these categories can further be divided between those held long or sold short. The Company has the option to measure certain financial assets and financial liabilities at fair value with changes in fair value recognized in earnings each period. The election is made on an instrument by instrument basis at initial recognition of an asset or liability or upon an event that gives rise to a new basis of accounting for that instrument. The Company has elected the fair value option for certain of its investments held by its operating companies. This option has been elected because the Company believes that it is consistent with the manner in which the business is managed as well as the way that financial instruments in other parts of the business are recorded. Securities — Securities with values based on quoted market prices in active markets for identical assets are classified within level 1 of the fair value hierarchy. These securities include active listed equities, certain U.S. government and sovereign obligations, Exchange Traded Funds ("ETFs"), mutual funds and certain money market securities. The Company does not adjust the quoted price for such instruments, even in situations where the Company holds a large position and a sale could reasonably impact the quoted price. Certain positions for which trading activity may not be readily visible, consisting primarily of convertible debt, corporate debt and loans and restricted equities, are stated at fair value and classified within level 2 of the fair value hierarchy. The estimated fair values assigned by management are determined in good faith and are based on available information considering, trading activity, broker quotes, quotations provided by published pricing services, counterparties and other market participants, and pricing models using quoted inputs, and do not necessarily represent the amounts which might ultimately be realized. As level 2 investments include positions that are not always traded in active markets and/or are subject to transfer restrictions, valuations may be adjusted to reflect illiquidity and/or non-transferability. Derivative contracts — Derivative contracts can be exchange-traded or privately negotiated over-the-counter (“OTC”). Exchange-traded derivatives, such as futures contracts and exchange-traded option contracts, are typically classified within level 1 or level 2 of the fair value hierarchy depending on whether or not they are deemed to be actively traded. OTC derivatives, such as generic forwards, swaps and options, have inputs which can generally be corroborated by market data and are therefore classified within level 2. OTC derivatives, such as swaps and options where market data is not readily available or observable are classified as level 3. Other investments — Other investments consist primarily of portfolio funds, real estate investments and equity method investments, which are valued as follows : i. Portfolio funds— Portfolio funds (“Portfolio Funds”) include interests in funds and investment companies which may be managed by the Company or its affiliates. The Company follows US GAAP regarding fair value measurements and disclosures relating to investments in certain entities that calculate net asset value (“NAV”) per share (or its equivalent). The guidance permits, as a practical expedient, an entity holding investments in certain entities that either are investment companies as defined by the American Institute of Certified Public Accountants ("AICPA") Audit and Accounting Guide, Investment Companies, or have attributes similar to an investment company, and calculate net asset value per share or its equivalent for which the fair value is not readily determinable, to measure the fair value of such investments on the basis of that NAV per share, or its equivalent, without adjustment. In accordance with US GAAP, investments which are valued using NAV per share as a practical expedient are not categorized within the fair value hierarchy. ii. Real estate investments— Real estate debt and equity investments are valued at fair value. The fair value of real estate investments are estimated based on the price that would be received to sell an asset in an orderly transaction between marketplace participants at the measurement date. Real estate investments without a public market are valued based on assumptions and valuation techniques used by the Company. Such valuation techniques may include discounted cash flow analysis, prevailing market capitalization rates or earnings multiples applied to earnings from the investment, analysis of recent comparable sales transactions, actual sale negotiations and bona fide purchase offers received from third parties, consideration of the amount that currently would be required to replace the asset, as adjusted for obsolescence, as well as independent external appraisals. In general, the Company considers several valuation techniques when measuring the fair value of a real estate investment. However, in certain circumstances, a single valuation technique may be appropriate. Real estate investments are reviewed on a quarterly basis by the Company for significant changes at the property level or a significant change in the overall market which would impact the value of the real estate investment resulting in unrealized appreciation or depreciation. Real estate and capital markets are cyclical in nature. Property and investment values are affected by, among other things, the availability of capital, occupancy rates, rental rates and interest and inflation rates. In addition, the Company invests in real estate and real estate related investments for which no liquid market exists. The market prices for such investments may be volatile and may not be readily ascertainable. Amounts ultimately realized by the Company from investments sold may differ from the fair values presented, and the differences could be material. The Company's real estate investments are typically categorized as level 3 investments within the fair value hierarchy as management uses significant unobservable inputs in determining their estimated fair value. See Notes 6 and 7 for further information regarding the Company's investments, including equity method investments, and fair value measurements.
Due From / Due to Related Parties	Due from/due to related parties The Company may advance amounts and pay certain expenses on behalf of employees of the Company or other affiliates of the Company. These amounts settle in the ordinary course of business. Such amounts are included in due from and due to related parties, respectively, on the accompanying consolidated statements of financial condition.
Receivable from and payable to brokers	Receivable from and payable to brokers Receivable from and payable to brokers, includes cash held at clearing brokers, amounts receivable or payable for unsettled transactions, monies borrowed and proceeds from short sales equal to the fair value of securities sold, but not yet purchased. Pursuant to the Company's prime broker agreements, these balances are presented net (assets less liabilities) across balances with the same broker.
Fees Receivable	Fees receivable Fees related to security transactions are reported net of an allowance for doubtful debts. An allowance for doubtful debts is taken on any commission receivables aged over 180 days. Corporate finance and syndicate receivables, include receivables relating to the Company’s investment banking and advisory engagements net of allowance for doubtful accounts. The Company records this allowance for doubtful accounts on these receivables on a specific identification basis. The future collectability of the receivables is reviewed on a monthly basis based on the following factors: aging (usually if outstanding greater than 90 days), known financial stability of the paying company as well as any other factors that might impact the collection of the outstanding fees. Management and incentive fees are earned as the managing member, general partner and/or investment manager to the Company's funds and are recognized on an accrual basis when earned.
Securities Borrowed and Loaned Policy	Securities borrowed and securities loaned Securities borrowed and securities loaned are carried at the amounts of cash collateral advanced or received on a gross basis. The related rebates are recorded in the accompanying consolidated statements of operations as interest and dividends income and interest and dividends expense. Securities borrowed transactions require the Company to deposit cash collateral with the lender. With respect to securities loaned, the Company receives cash collateral from the borrower. The initial collateral advanced or received approximates or is greater than the market value of securities borrowed or loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or returned, as necessary. Securities borrowed and loaned may also result in credit exposures for the Company in an event that the counterparties are unable to fulfill their contractual obligations. The Company minimizes its credit risk by continuously monitoring its credit exposure and collateral values by demanding additional or returning excess collateral in accordance with the netting provisions available in the master securities lending contracts in place with the counterparties. Fees and interest received or paid are recorded in interest and dividends income and interest and dividends expense, respectively, on an accrual basis in the accompanying consolidated statements of operations. In cases where the fair value basis of accounting is elected, any resulting change in fair value would be reported in net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. Accrued interest income and expense are recorded in receivable from brokers, dealers and clearing organizations and payable to brokers, dealers and clearing organizations, respectively, on an accrual basis in the accompanying consolidated statements of financial condition. At December 31, 2017 , the Company did not have any securities lending transactions for which fair value basis of accounting was elected.
Fixed Assets	Fixed Assets Fixed assets are stated at cost less accumulated depreciation or amortization. Leasehold improvements are amortized on a straight-line basis over the lesser of their useful life or lease term. When the Company commits to a plan to abandon fixed assets or leasehold improvements before the end of its original useful life, the estimated depreciation or amortization period is revised to reflect the shortened useful life of the asset. Other fixed assets are depreciated on a straight-line basis over their estimated useful lives. Aircraft and related equipment, which are leased out under operating leases, are carried at cost less accumulated depreciation and are depreciated to estimated residual value using the straight-line method over the lease term or estimated useful life of the asset. Any assets received at the end of the lease are marked to the lower of cost or fair value with the adjustment recorded in other income. Asset Depreciable Lives Depreciation and/or Amortization Method Telephone and computer equipment 3-5 years Straight-line Computer software 3-8 years Straight-line Furniture and fixtures 5 years Straight-line Leasehold improvements 2-15 years Straight-line Capitalized lease asset 5 years Straight-line Aircraft and related equipment 10-20 years Straight-line Modifications to aircraft 4-10 years Straight-line
Goodwill and Intangible Assets, Policy	Goodwill and intangible assets Goodwill represents the excess of the purchase price consideration of acquired companies over the estimated fair value assigned to the individual assets acquired and liabilities assumed. Goodwill is allocated to the Company's reporting units at the date the goodwill is initially recorded. Once goodwill has been allocated to the reporting units, it generally no longer retains its identification with a particular acquisition, but instead becomes identifiable with the reporting unit. As a result, all of the fair value of each reporting unit is available to support the value of goodwill allocated to the unit. In accordance with US GAAP, the Company tests goodwill for impairment on an annual basis, at December 31 st each year, or at an interim period if events or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Under US GAAP, the Company tests goodwill for impairment by assessing the qualitative factors including, macroeconomic environment, industry and market specific conditions, financial performance and events specific to the reporting unit to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying amount. Based on the results of the qualitative assessment the Company performs the two-step goodwill impairment test. The first step requires a comparison of the fair value of the reporting unit to its carrying value, including goodwill. If the fair value of the reporting unit exceeds its carrying value, the related goodwill is not considered impaired and no further analysis is required. If the carrying value of the reporting unit exceeds the fair value, there is an indication that the related goodwill might be impaired and the step two is performed to measure the amount of impairment, if any. The second step of the goodwill impairment test compares the implied fair value of the reporting unit's goodwill with its carrying amount to measure the amount of impairment, if any. The implied fair value of goodwill is determined in the same manner as the amount of goodwill recognized in a business combination. In other words, the estimated fair value of the reporting unit is allocated to all of its assets and liabilities (including any unrecognized intangible assets) as if the reporting unit had been acquired in a business combination and the fair value of the reporting unit was the purchase price paid. If the carrying amount of the reporting unit goodwill exceeds the implied fair value of that goodwill, an impairment is recognized in an amount equal to that excess. Goodwill impairment tests involve significant judgment in determining the estimates of future cash flows, discount rates, economic forecast and other assumptions which are then used in acceptable valuation techniques, such as the market approach (earning and/or transactions multiples) and/or income approach (discounted cash flow method). Changes in these estimates and assumptions could have a significant impact on the fair value and any resulting impairment of goodwill. See Note 12 for further discussion. Intangible assets with finite lives are amortized over their estimated average useful lives. The Company does not have any intangible assets deemed to have indefinite lives. Intangible assets are tested for potential impairment whenever events or changes in circumstances suggest that an asset or asset group's carrying value may not be fully recoverable. Similar to goodwill impairment test, an impairment loss, calculated as the difference between the estimated fair value and the carrying value of an asset or asset group, is recognized in the accompanying consolidated statements of operations if the sum of the estimated undiscounted cash flows relating to the asset or asset group is less than the corresponding carrying value.
Debt	Debt Long-term debt is carried at the principal amount borrowed net of any unamortized discount/premium. The discount is accreted to interest expense using the effective interest method over the remaining life of the underlying debt obligations. Accrued but unpaid coupon interest is included in accounts payable, accrued expenses and other liabilities in the accompanying consolidated statements of financial condition.
Deferred rent	Deferred rent Deferred rent primarily consists of step rent, allowances from landlords and valuing the Company's lease properties acquired through business combinations in accordance with US GAAP. Step rent represents the difference between actual operating lease payments due and straight-line rent expense, which is recorded by the Company over the term of the lease, including the build-out period. This amount is recorded as deferred rent in the early years of the lease, when cash payments are generally lower than straight-line rent expense, and reduced in the later years of the lease when payments begin to exceed the straight-line expense. Landlord allowances are generally comprised of amounts received and/or promised to the Company by landlords and may be received in the form of cash or free rent. These allowances are part of the negotiated terms of the lease. The Company records a receivable from the landlord and a deferred rent liability when the allowances are earned. This deferred rent is amortized into income (through lower rent expense) over the term (including the pre-opening build-out period) of the applicable lease, and the receivable is reduced as amounts are received from the landlord. Liabilities resulting from valuing the Company's leased properties acquired through business combinations are quantified by comparing the current fair value of the leased space to the current rental payments on the date of acquisition. Deferred rent, included in accounts payable, accrued expenses and other liabilities in the accompanying consolidated statements of financial condition, as of December 31, 2017 and 2016 is $12.8 million and $10.3 million , respectively.
Legal Costs, Policy	Legal reserves In accordance with US GAAP, the Company establishes reserves for contingencies when the Company believes that it is probable that a loss has been incurred and the amount of loss can be reasonably estimated. The Company discloses a contingency if there is at least a reasonable possibility that a loss may have been incurred and there is no reserve for the loss because the conditions above are not met. The Company's disclosure includes an estimate of the reasonably possible loss or range of loss for those matters, for which an estimate can be made. Neither reserve nor disclosure is required for losses that are deemed remote.
Capital withdrawals payable	Capital withdrawals payable Capital withdrawals from the Consolidated Funds are recognized as liabilities, net of any incentive income, when the amount requested in the withdrawal notice represents an unconditional obligation at a specified or determined date (or dates) or upon an event certain to occur. This generally may occur either at the time of the receipt of the notice, or on the last day of a reporting period, depending on the nature of the request. As a result, withdrawals paid after the end of the year, but based upon year-end capital balances are reflected as liabilities at the balance sheet date.
Redeemable non-controlling interests in consolidated subsidiaries	Redeemable non-controlling interests in consolidated subsidiaries Redeemable non-controlling interests represent the pro rata share of the book value of the financial positions and results of operations attributable to the other owners of the consolidated subsidiaries. Redeemable non-controlling interests related to Consolidated Funds are generally subject to annual, semi-annual or quarterly withdrawals or redemptions by investors in these funds, sometimes following the expiration of a specified period of time (generally one year), or may only be withdrawn subject to a redemption fee (generally ranging from 1% to 5% ). Likewise, non-controlling interests related to certain other consolidated entities are generally subject to withdrawal, redemption, transfer or put/call rights that permit such non-controlling investors to withdraw from the entities on varying terms and conditions. Because these non-controlling interests are redeemable at the option of the non-controlling interests, they have been classified as temporary equity in the accompanying consolidated statements of financial condition. When redeemed amounts become legally payable to investors on a current basis, they are reclassified as a liability.
Stockholders' Equity, Policy	Treasury stock In accordance with US GAAP relating to repurchases of an entity's own outstanding common stock, the Company records the purchases of stock held in treasury at cost and reports them separately as a deduction from total stockholders' equity on the accompanying consolidated statements of financial condition and changes in equity.
Comprehensive Income, Policy	Comprehensive income (loss) Comprehensive income (loss) consists of net income and other comprehensive income (loss). The Company's other comprehensive income (loss) is comprised of foreign currency cumulative translation adjustments.
Revenue Recognition Leases, Operating	Revenue recognition The Company's principle sources of revenue are derived from two segments: an investment management segment and a broker-dealer segment, as more fully described below. Our investment management segment generates revenue through three principle sources: management fees, incentive income and investment income from the Company's own capital. Our broker-dealer segment generates revenue through three principle sources: investment banking, brokerage and investment income. Management fees The Company earns management fees from affiliated private funds and certain managed accounts that it serves as the investment manager based on assets under management. The actual management fees received vary depending on distribution fees or fee splits paid to third parties either in connection with raising the assets or structuring the investment. Several management companies of the private funds are owned jointly by the Company and third parties. Accordingly, the management fees generated by these funds are split between the Company and these third parties. Pursuant to US GAAP, these fees received by the management companies that are accounted for under the equity method of accounting and are reflected under net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. Management fees are generally paid on a quarterly basis at the beginning of each quarter in arrears and are prorated for capital inflows and redemptions. While some investors may have separately negotiated fees, in general the management fees are as follows: • Private Funds. Management fees for the Company's private funds, including the private healthcare fund, are generally charged at an annual rate of up to 2% of assets under management or notional trading level. Management fees are generally calculated monthly based on assets under management at the end of each month before incentive income . • Real Estate. Management fees from the Company's real estate business are generally charged at an annual rate from 0.25% to 1.50% of total capital commitments during the investment period and of invested capital or net asset value of the applicable fund after the investment period has ended. Management fees are typically paid to the general partners on a quarterly basis, at the beginning of the quarter in arrears, and are prorated for changes in capital commitments throughout the investment period and invested capital after the investment period. • HealthCare Royalty Partners. In HealthCare Royalty Partners main funds, during the investment period (as defined in the relevant partnership agreements), management fees are generally charged at an annual rate of 1% to 2% of committed capital. After the investment period, management fees for these funds are generally charged at an annual rate of 0.5% to 2% o f the net asset value or the aggregate cost basis of the unrealized investments held by the funds. For the other funds (and managed accounts) managed by Healthcare Royalty Partners, the management fee ranges from 0.2% to 1% and there is no adjustment based on an investment period. Management fees for the HealthCare Royalty Partners funds are calculated on a quarterly basis . • Cowen Trading Strategies. Advisory fees for the Company's collateral management advisory business are typically paid quarterly based on assets under management but generally subject to a minimum fee. Incentive income The Company earns incentive income based on net profits (as defined in the respective investment management agreements) with respect to certain of the Company's funds and managed accounts, allocable for each fiscal year that exceeds cumulative unrecovered net losses, if any, that have been carried forward from prior years. For the products the Company offers, incentive income earned is typically up to 20% for private funds (in certain cases on performance in excess of a benchmark), of the net profits earned for the full year that are attributable to each fee-paying investor. Generally, incentive income on real estate funds is earned after the investor has received a full return of their invested capital, plus a preferred return. However, for certain real estate funds, the Company is entitled to receive incentive fees earlier, provided that the investors have received their preferred return on a current basis or on an investor by investor basis. These funds are generally subject to a potential clawback of these incentive fees upon the liquidation of the fund if the investor has not received a full return of its invested capital plus the preferred return thereon. Incentive income in the HealthCare Royalty Partners funds is generally earned only after investors receive a full return of their capital plus a preferred return. Several general partners of the Company's private funds are jointly owned by the Company and third parties. Accordingly, the incentive fees generated by these funds are split between the Company and these third parties. Pursuant to US GAAP, incentive income received by the general partners that are accounted for under the equity method of accounting are reflected under net gains (losses) on securities, derivatives and other investments in the accompanying consolidated statements of operations. In periods following a period of a net loss attributable to an investor, the Company generally does not earn incentive income on any future profits attributable to that investor until the accumulated net loss from prior periods is recovered, an arrangement commonly referred to as a “high-water mark.” The Company has elected to record incentive income revenue in accordance with “Method 2” of US GAAP. Under Method 2, the incentive income from the Company's investment management products for any period is based upon the net profits of those investment management products at the reporting date. Any incentive income recognized in the accompanying consolidated statement of operations may be subject to future reversal based on subsequent negative performance prior to the conclusion of the fiscal year, when all contingencies have been resolved. Carried interest in the real estate funds and HealthCare Royalty Partners funds are subject to clawback to the extent that the carried interest actually distributed to date exceeds the amount due to the Company based on cumulative results. As such, the accrual for potential repayment of previously received carried interest, which is a component of accounts payable, accrued expenses and other liabilities, represents all amounts previously distributed to the Company, less an assumed tax liability, that would need to be repaid to certain funds if these funds were to be liquidated based on the current fair value of the underlying funds' investments as of the reporting date. The actual clawback liability does not become realized until the end of a fund's life. Investment Banking The Company earns investment banking revenue primarily from fees associated with public and private capital raising transactions and providing strategic advisory services. Investment banking revenues are derived primarily from small and mid-capitalization companies within the Company's Target Sectors. Investment banking revenue consists of underwriting fees, strategic/financial advisory fees and placement and sales agent fees. • Underwriting fees. The Company earns underwriting fees in securities offerings in which the Company acts as an underwriter, such as initial public offerings, follow-on equity offerings, debt offerings, and convertible security offerings. Fee revenue relating to underwriting commitments is recorded when all significant items relating to the underwriting process have been completed and the amount of the underwriting revenue has been determined. This generally is the point at which all of the following have occurred: (i) the issuer's registration statement has become effective with the SEC or the other offering documents are finalized; (ii) the Company has made a firm commitment for the purchase of securities from the issuer; and (iii) the Company has been informed of the number of securities that it has been allotted. When the Company is not the lead manager for an underwriting transaction, management must estimate the Company's share of transaction-related expenses incurred by the lead manager in order to recognize revenue. Transaction-related expenses are deducted from the underwriting fee and therefore reduce the revenue the Company recognizes as co-manager. Such amounts are adjusted to reflect actual expenses in the period in which the Company receives the final settlement, typically within 90 days following the closing of the transaction. • Strategic/financial advisory fees. The Company's strategic advisory revenues include success fees earned in connection with advising companies, principally in mergers, acquisitions and restructuring transactions. The Company also earns fees for related advisory work such as providing fairness opinions. The Company records strategic advisory revenues when the services for the transactions are completed under the terms of each assignment or engagement and collection is reasonably assured. Expenses associated with such transactions are deferred until the related revenue is recognized or the engagement is otherwise concluded. • Placement and sales agent fees. The Company earns agency placement fees and sales agent commissions in non-underwritten transactions such as private placements of loans and debt and equity securities, including, private investment in public equity transactions (“PIPEs”), and as sales agent in at-the-market offerings of equity securities. The Company records placement revenues (which may be in cash and/or securities) when the services for the transactions are completed under the terms of each assignment or engagement and collection is reasonably assured. The Company records sales agent commissions on a trade date basis. Expenses associated with such transactions are deferred until the related revenue is recognized or the engagement is otherwise concluded. Brokerage Brokerage revenue consists of commissions, principal transactions, equity and credit research fees and trade conversion revenue. • Commissions. Commission revenue includes fees from executing and clearing client transactions and commission sharing arrangements. These fees are recognized on a trade date basis. The Company permits institutional customers to allocate a portion of their commissions to pay for research products and other services provided by third parties. The amounts allocated for those purposes are commonly referred to as soft dollar arrangements. Commissions on soft dollar brokerage are recorded net of the related expenditures on an accrual basis. The costs of commission recapture arrangements are recorded on an accrual basis for each eligible trade and shown net of commission revenue. Commission revenues also includes fees from making algorithms available to clients. • Principal transactions. Principal transactions revenue includes net trading gains and losses from the Company's market-making activities in over-the-counter equity and fixed income securities, trading of convertible securities, and trading gains and losses on inventory and other Company positions, which include warrants previously received as part of investment banking transactions. In certain cases, the Company provides liquidity to clients by buying or selling blocks of shares of listed stocks without previously identifying the other side of the trade at execution, which subjects the Company to market risk. These positions are typically held for a very short duration. • Equity and credit research fees. Equity and credit research fees are paid to the Company for providing equity and credit research. Revenue is recognized once an arrangement exists, access to research has been provided, the fee amount is fixed or determinable, and collection is reasonably assured. • Trade conversion revenue. Trade conversion revenue includes the fee earned from converting foreign securities into an American Depository Receipt (“ADR”) and the fee earned from converting an ADR into foreign securities on behalf of customers, and margins earned from facilitating customer foreign exchange transactions. Trade conversion revenue is recognized on a trade date basis. Interest and dividends Interest and dividends are earned by the Company from various sources. The Company receives interest and dividends primarily from securities finance activities and securities held by the Company for purposes of investing capital, investments held by its Consolidated Funds and its brokerage balances. Interest is recognized on an accrual basis and interest income is recognized on the debt of those issuers that is deemed collectible. Interest income and expense includes premiums and discounts amortized and accreted on debt investments based on criteria determined by the Company using the effective yield method, which assumes the reinvestment of all interest payments. Dividends are recognized on the ex-dividend date. Reimbursement from affiliates The Company allocates, at its discretion, certain expenses incurred on behalf of its private fund and real estate businesses. These expenses relate to the administration of such subsidiaries and assets that the Company manages for its funds. In addition, pursuant to the funds' offering documents, the Company charges certain allowable expenses to the funds, including charges and personnel costs for legal, compliance, accounting, tax compliance, risk and technology expenses that directly relate to administering the assets of the funds. Such expenses that have been reimbursed at their actual costs are included in the accompanying consolidated statements of operations as employee compensation and benefits, professional, advisory and other fees, communications, occupancy and equipment, client services and business development and other. Aircraft lease revenue Aircraft lease revenue associated with the Company's aircraft leasing business is recorded on a straight-line basis over the term of the lease, net of deferred rent and/or prepaid initial direct costs. Reinsurance-related contracts Premiums for reinsurance-related contracts are earned over the coverage period. In most cases, premiums are recognized as revenues ratably over the term of the contract with unearned premiums computed on a monthly basis. For each of its contracts, the Company determines if the contract provides indemnification against loss or liability relating to insurance risk, in accordance with US GAAP. If the Company determines that a contract does not expose it to a reasonable possibility of a significant loss from insurance risk, the Company records the contract under the deposit method of accounting with any net amount receivable reflected as an asset in other assets, and any net amount payable reflected as a liability within accounts payable, accrued expenses and other liabilities on the consolidated statements of financial condition. The liabilities for losses and loss adjustment expenses are recorded at the estimated ultimate payment amounts, including reported losses. Estimated ultimate payment amounts are based upon (1) reports of losses from policyholders, (2) individual case estimates and (3) estimates of incurred but not reported losses. Provisions for losses and loss adjustment expenses are charged to earnings after deducting amounts recovered and estimates of recoverable amounts and are included in other expenses on the consolidated statements of operations. Costs of acquiring new policies, which vary with and are directly related to the production of new policies, have been deferred to the extent that such costs are deemed recoverable from future premiums or gross profits. Such costs include commissions and allowances as well as certain costs of policy issuance and underwriting and are included within other assets on the consolidated statements of financial condition.
Investment Transactions and Related Income / Expenses	Investments transactions and related income/expenses Purchases and sales of securities, net of commissions, and derivative contracts, and the related revenues and expenses are recorded on a trade date basis with net trading gains and losses included as a component of net gains (losses) on securities, derivatives and other investments, and with respect to the Consolidated Funds and other real estate entities as a component of net realized and unrealized gains (losses) on investments and other transactions and net realized and unrealized gains (losses) on derivatives, respectively, in the accompanying consolidated statements of operations.
Share-based Compensation, Option and Incentive Plans Policy	Share-based compensation The Company accounts for its share-based awards granted to individuals as payment for employee services in accordance with US GAAP and values such awards based on grant date fair value. Unearned compensation associated with share-based awards is amortized over the vesting period of the option or award. The Company estimates forfeiture for equity-based awards that are not expected to vest. See Note 19 for further information regarding the Company's share-based compensation plans.
Lease, Policy	Leases The Company leases certain facilities and equipment used in its operations. The Company evaluates and classifies its leases as operating or capital leases for financial reporting purposes. Assets held under capital leases are included in fixed assets. Operating lease expense is recorded on a straight-line basis over the lease term. Landlord incentives are recorded as deferred rent and amortized, as reductions to lease expense, on a straight-line basis over the life of the applicable lease.
Income Tax, Policy	Income taxes The Company accounts for income taxes in accordance with US GAAP which requires the recognition of tax benefits or expenses based on the estimated future tax effects of temporary differences between the financial statement and tax basis of its assets and liabilities. The effect on deferred taxes of a change in tax rates is recognized as income or loss in the period that includes the enactment date. Valuation allowances are established to reduce deferred tax assets to an amount that is more likely than not to be realized. We evaluate our deferred tax assets for recoverability considering negative and positive evidence, including our historical financial performance, projections of future taxable income, future reversals of existing taxable temporary differences, and tax planning strategies. We record a valuation allowance against our deferred tax assets to bring them to a level that it is more likely than not to be utilized. In evaluating the need for a valuation allowance, we estimate future taxable income based on management approved business plans. This process involves significant management judgment about assumptions that are subject to change from period to period. Because the recognition of deferred tax assets requires management to make significant judgments about future earnings, the periods in which items will impact taxable income and the application of inherently complex tax laws, we have identified the assessment of deferred tax assets and the need for any related valuation allowance as a critical accounting estimate. US GAAP clarifies the accounting for uncertainty in income taxes recognized in an enterprise’s financial statements, requiring the Company to determine whether a tax position is more likely than not to be sustained upon examination, including resolution of any related appeals or litigation processes, based on the technical merits of the position. For tax positions meeting the more likely than not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement with the relevant taxing authority. The Company recognizes accrued interest and penalties related to its uncertain tax positions as a component of income tax expense. In accordance with federal and state tax laws, the Company and its subsidiaries file consolidated federal, state, and local income tax returns as well as stand-alone state and local tax returns. The Company also has subsidiaries that are resident in foreign countries where tax filings have to be submitted on a stand-alone or combined basis. These subsidiaries are subject to tax in their respective countries and the Company is responsible for and, thus, reports all taxes incurred by these subsidiaries in the consolidated statement of operations. The countries where the Company owns subsidiaries and has tax filing obligations are the United Kingdom, Luxembourg, and Hong Kong.
Foreign Currency Transactions and Translations Policy	Foreign currency transactions The Company consolidates certain foreign subsidiaries that have designated a foreign currency as their functional currency. For entities that have designated a foreign currency as their functional currency, assets and liabilities are translated into U.S. dollars based on current rates, which are the spot rates prevailing at the end of each statement of financial condition date, and revenues and expenses are translated at historical rates, which are the average rates for the relevant periods. The resulting translation gains and losses, and the tax effects of such gains and losses, are recorded in accumulated other comprehensive income (loss), a separate component of stockholders' equity. For subsidiaries that have designated the U.S. Dollar as their functional currency, securities and other assets and liabilities denominated in foreign currencies are translated into U.S. Dollar amounts at the date of valuation. Purchases and sales of securities and other assets and liabilities and the related income and expenses denominated in foreign currencies are translated into U.S. Dollar amounts on the respective dates of the transactions. The Company does not isolate that portion of the results of operations resulting from changes in foreign exchange rates on these balances from fluctuations arising from changes in market prices of securities and other assets/liabilities held or sold. Such fluctuations are included in the accompanying consolidated statements of operations as a component of net gains (losses) on securities, derivatives and other investments. Gains and losses primarily relating to foreign currency broker balances are included in Other income (loss) in the accompanying consolidated statements of operations.
Recently issued accounting pronouncements	Recently issued accounting pronouncements In May 2014, the FASB issued guidance which amends and supersedes the revenue recognition requirements and most industry-specific guidance related to revenue recognition and creates a single source of guidance. The new guidance outlines the principles an entity must apply to measure and recognize revenue and related cash flows. The guidance also provides a model for the measurement and recognition of gains and losses on the sale of certain non-financial assets. For public business entities, the guidance is effective for reporting periods beginning after December 15, 2017. The Company has identified its revenues and costs that are within the scope of the new guidance and concluded that the guidance is not applicable to financial instruments, lease and insurance contracts and therefore, will not impact investment income, lease or reinsurance revenue. The Company continues to implement and evaluate the potential impact of the guidance on the consolidated results of operations, related disclosures and internal controls over financial reporting. For its investment management businesses, the Company will recognize performance / incentive fees when such revenue is not subject to significant reversal in the future. For certain of the funds offered by the Company, primarily the closed ended funds, the Company will defer the recognition of performance fees until such fees are no longer subject to reversal or clawback, which will cause a delay in the recognition of these fees as revenue. Certain of the Company's funds qualify for the equity method of accounting treatment in line with the conclusions reached by AICPA’s Revenue Recognition Task Force. Therefore, the Company elected to account for the revenue as equity pick up under equity method of accounting. The placement fees paid to certain placement agents for its capital raising activities will qualify to be capitalized and amortized as part of contract acquisition costs. The Company does not currently anticipate that its current methods of recognizing investment banking revenues will be materially impacted by the new guidance. The current broker-dealer industry treatment of netting deal expenses with investment banking revenues will change under the new guidance. As a result of adopting of the new guidance, deal expenses will generally be presented on a gross basis in the consolidated statements of operations, resulting in higher revenues and higher non-compensation expenses with no impact on net income. The Company is closely monitoring the AICPA's industry task forces on broker-dealers and asset management, the AICPA’s Revenue Recognition Working Group and the AICPA’s Financial Reporting Executive Committee as they continue to issue interpretive guidance. The Company has adopted this guidance effective as of January 1, 2018 using the modified retrospective approach under which the cumulative effect of applying the standard would be recognized at the date of initial application. In May 2017, the FASB issued guidance to clarify the application of modification accounting for stock compensation. The guidance was issued to reduce the diversity in practice under the current guidance. The new guidance requires an entity to apply modification accounting when there is a change in the fair value of the modified award and the original award, vesting conditions and the classification of the original awards. The amendments in this guidance are effective prospectively for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years. The Company will apply the new guidance for any modifications on or after the adoption date. In March 2017, the FASB issued guidance to amend the amortization period for certain purchased callable debt securities held at a premium. Under current guidance, entities generally amortize the premium as an adjustment of yield over the contractual life of the instrument. The new guidance shortened the amortization period for the premium to the earliest call date. The amendments do not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. The amendments in this guidance are effective for public business entities for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the impact of this guidance on the Company’s consolidated financial statements and does not expect this guidance to have a material impact on its statement of financial condition or its statement of operations as the Company does not hold any material callable debt securities. In January 2017, the FASB issued guidance that simplifies the subsequent measurement of goodwill. The new guidance eliminated Step 2 from the goodwill impairment test which was required in computing the implied fair value of goodwill. Instead, under the new amendments, an entity should perform its annual or interim goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. If applicable, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss. The amendments in this guidance are effective for public business entities for annual and interim goodwill impairment tests performed in fiscal years beginning after December 15, 2019 with early adoption permitted after January 1, 2017. The Company is currently evaluating the impact of this guidance on the Company’s consolidated financial statements. The Company expects this guidance to simplify its goodwill impairment analysis. In January 2017, the FASB issued guidance which clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. Under the current guidance, there are three elements of a business-inputs, processes, and outputs. While an integrated set of assets and activities (collectively, a “set”) that is a business usually has outputs, outputs are not required to be present. In addition, all the inputs and processes that a seller uses in operating a set are not required if market participants can acquire the set and continue to produce outputs, for example, by integrating the acquired set with their own inputs and processes. The new guidance provides a screen to determine when a set is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired (or disposed of) is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. For public business entities, the guidance is effective prospectively for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years. The Company will use the new definition of a business for its future business combination activities. In November 2016, the FASB issued guidance which reduces the diversity in practice as to how changes in restricted cash are presented and classified in the statement of cash flows. The guidance requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The guidance does not provide a definition of restricted cash or restricted cash equivalents. For public business entities, the guidance is effective prospectively for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years. The Company currently presents its restricted cash and changes in its restricted cash, separately on its consolidated statements of financial condition and consolidated statements of cash flows respectively. Since the guidance only affects the presentation of restricted cash on the statement of cash flows, the Company does not expect this guidance to have any impact on its consolidated financial statements and will present total cash and cash equivalents from the adoption date. In August 2016, the FASB issued guidance which reduces the diversity in practice as to how certain cash receipts and cash payments are presented and classified in the statement of cash flows. This guidance addresses eight specific cash flow issues with the objective of reducing the existing and potential future diversity in practice. The amendments in this guidance are effective for public business entities for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years. The Company is currently evaluating the impact of this guidance on the Company’s cash flows presentation. Since the guidance only affects the presentation of statement of cash flows, the Company does not expect this guidance to have any impact on consolidated financial statements. The Company notes that its current presentation is already in line with most of the specific cash flow issues identified in the guidance. In February 2016, the FASB issued guidance which amends and supersedes its previous guidance regarding leases. The new guidance requires the lessee to recognize the right to use assets and lease liabilities that arise from leases and present them in its statement of financial condition. The recognition of these lease assets and lease liabilities represents a change from previous US GAAP, which did not require lease assets and lease liabilities to be recognized for most leases. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from previous US GAAP. There continues to be a differentiation between finance leases and operating leases. However, the principal difference from previous guidance is that the lease assets and lease liabilities arising from operating leases should be recognized in the statement of financial condition. For public business entities the guidance is effective for reporting periods beginning after December 15, 2018. The Company is currently evaluating the impact of this guidance on the Company’s financial condition and its disclosures. The Company notes that a significant majority of the Company’s leases represent operating real estate leases for its respective offices and will require the gross up on its statement of financial condition.
Earnings Per Share	Diluted earnings per common share are calculated by adjusting the weighted average outstanding shares to assume conversion of all potentially dilutive items. The Company uses the treasury stock method to reflect the potential dilutive effect of the warrants (see Note 6 (a)), unexercised stock options, unvested restricted shares, restricted stock units, and SAR's. In calculating the number of dilutive shares outstanding, the shares of common stock underlying unvested restricted shares and restricted stock units are assumed to have been delivered, and options and warrants are assumed to have been exercised, for the entire period being presented. The assumed proceeds from the assumed vesting, delivery and exercising were calculated as the amount of compensation cost attributed to future services and not yet recognized.
Segment Reporting	The performance measure for these segments is Economic Income (Loss), which management uses to evaluate the financial performance of and make operating decisions for the segments including determining appropriate compensation levels. Expenses not directly associated with specific segments are allocated based on the most relevant measures applicable, including headcount, square footage and other factors. In general, Economic Income (Loss) is a pre-tax measure that (i) eliminates the impact of consolidation for consolidated funds and excludes (ii) goodwill and intangible impairment (iii) certain other transaction-related adjustments and/or reorganization expenses (iv) the bargain purchase gain which resulted from the Convergex Group acquisition (v) certain costs associated with debt and (vi) preferred stock dividends. In addition, Economic Income (Loss) revenues include investment income that represents the income the Company has earned in investing its own capital, including realized and unrealized gains and losses, interest and dividends, net of associated investment related expenses. For US GAAP purposes, these items are included in each of their respective line items. Economic Income (Loss) revenues also include management fees, incentive income and investment income earned through the Company's investment as a general partner in certain real estate entities and the Company's investment in the activist business. For US GAAP purposes, all of these items are recorded in other income (loss). In addition, Economic Income (Loss) expenses are reduced by reimbursement from affiliates, which for US GAAP purposes is presented gross as part of revenue. As further stated below, one major difference between Economic Income (Loss) and US GAAP net income (loss) is that Economic Income (Loss) presents the segments' results of operations without the impact resulting from the full consolidation of any of the Consolidated Funds. The consolidation of these funds results include the pro rata share of the income or loss attributable to other owners of such entities which is reflected in net income (loss) attributable to redeemable non-controlling interest in consolidated subsidiaries in the accompanying consolidated statements of operations. This pro rata share has no effect on the overall financial performance for the investment management segment, as ultimately, this income or loss is not income or loss for the investment management segment itself. Included in Economic Income (Loss) is the actual pro rata share of the income or loss attributable to the Company as an investor in such entities, which is relevant in management making operating decisions and evaluating financial performance.

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2017
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The table below summarizes the preliminary purchase price allocation of net tangible and intangible assets acquired and liabilities assumed as of June 1, 2017 : (dollars in thousands) Cash and cash equivalents $ 30,562 Segregated cash 129,025 Securities owned, at fair value 3,417 Securities borrowed 258,321 Deposits from clearing organizations 52,596 Receivable from brokers 62,983 Receivable from customers 43,469 Fees receivable 36,232 Fixed assets, net 1,325 Intangible assets 10,270 Other assets 7,528 Securities sold, not yet purchased, at fair value (71 ) Securities loaned (286,359 ) Payable to brokers (74,284 ) Payable to customers (11,801 ) Commission management payable (82,718 ) Compensation payable (31,083 ) Notes payable and other debt (857 ) Fees payable (5,414 ) Accounts payable, accrued expenses and other liabilities (33,570 ) Total identifiable net assets acquired and liabilities assumed 109,571 Goodwill/(Bargain purchase gain) (11,609 ) Total estimated purchase price $ 97,962
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block]	As of the acquisition date, the estimated fair value of the Company's intangible assets, as acquired through the acquisition, was $ 10.3 million . The allocation of the intangible assets is shown within the following table. Estimated intangible assets acquired Estimated average remaining useful lives (dollars in thousands) (in years) Intangible asset class Trade name $ 760 0.6 - 2.6 Intellectual property 1,790 5 Customer relationships 7,720 9 Total intangible assets $ 10,270
Finite-lived Intangible Assets Amortization Expense [Table Text Block]	The estimated amortization expense related to these intangible assets in future periods is as follows: (dollars in thousands) 2018 $ 1,258 2019 1,239 2020 1,216 2021 1,216 2022 1,007 Thereafter 2,931 $ 8,867
Business Acquisition, Pro Forma Information	Year Ended December 31, 2017 2016 (dollars in thousands, except per share data) (unaudited) Revenues $ 733,744 $ 681,655 Net income (loss) attributable to Cowen Inc. stockholders (84,671 ) (50,516 ) Net income (loss) per common share: Basic (a) $ (2.75 ) $ (1.68 ) Diluted (a) (2.75 ) (1.68 ) (a) Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.

Significant Accounting Polici42

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Property, Plant and Equipment Useful Life	Asset Depreciable Lives Depreciation and/or Amortization Method Telephone and computer equipment 3-5 years Straight-line Computer software 3-8 years Straight-line Furniture and fixtures 5 years Straight-line Leasehold improvements 2-15 years Straight-line Capitalized lease asset 5 years Straight-line Aircraft and related equipment 10-20 years Straight-line Modifications to aircraft 4-10 years Straight-line

Investments of Operating Enti43

Investments of Operating Entities and Consolidated Funds - (Tables)	12 Months Ended
	Dec. 31, 2017
Investment Holdings [Line Items]
Marketable Securities	As of December 31, 2017 and 2016 , securities owned, at fair value consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Common stocks (b) $ 640,065 $ 669,655 Preferred stock (b) 9,604 15,811 Warrants and rights (b) 9,604 8,335 U.S. Government securities (a) 2,807 3,780 Corporate bonds (d) 4,909 2,477 Convertible bonds (c) 282 250 Trade claims 5,950 562 Mutual funds (b) — 6 $ 673,221 $ 700,876 (a) As of December 31, 2017 , maturities ranged from February 2018 to June 2018 with an interest rate of 0% . As of December 31, 2016 , maturities ranged from February 2017 to December 2017 with an interest rate of 0% . (b) The Company has elected the fair value option for investments in securities of preferred and common stocks with a fair value of $6.0 million and $5.2 million , respectively, at December 31, 2017 and $7.0 million and $5.2 million , respectively, at December 31, 2016 . At December 31, 2017 , the Company elected the fair value option for investments in warrants and rights with a fair value of $2.4 million . At December 31, 2016 the Company elected the fair value option for investments in mutual funds with a fair value of $0.1 million . (c) As of December 31, 2017 , maturities ranged from February 2018 to March 2018 and interest rates ranged from 5% to 12% . As of December 31, 2016 , the maturity was March 2018 with an interest rate of 8% . (d) As of December 31, 2017 , maturities ranged from October 2018 to May 2040 and interest rates ranged from 0.00% to 10.75% . As of December 31, 2016 , maturities ranged from January 2017 to January 2036 and interest rates ranged from 6.25% to 13.00% .
Schedule of Derivative Instruments	The Company's long and short exposure to derivatives is as follows: Receivable on derivative contracts As of December 31, 2017 2016 Number of contracts / Notional Value Fair value Number of contracts / Notional Value Fair value (dollars in thousands) Futures $ 3,819 $ 58 $ 12,421 $ 104 Currency forwards $ 233 5 $ 80,608 592 Swaps $ 164,664 10,942 $ 46,462 468 Options other (a) 283,112 58,172 256,097 21,539 Foreign currency options $ — — $ 57,051 198 $ 69,177 $ 22,901 (a) Includes index, equity, commodity future and cash conversion options. Payable for derivative contracts As of December 31, 2017 2016 Number of contracts / Notional Value Fair value Number of contracts / Notional Value Fair value (dollars in thousands) Futures $ 16,796 $ 242 $ 38,345 $ 642 Currency forwards $ 62,439 874 $ — — Swaps $ 11,595 71 $ 9,533 181 Options other (a) 57,043 41,563 23,726 19,939 $ 42,750 $ 20,762 (a) Includes index, equity, commodity future and cash conversion options. The following tables present the gross and net derivative positions and the related offsetting amount, as of December 31, 2017 and 2016 . This table does not include the impact of over collateralization. Gross amounts not offset in the Consolidated Statement of Financial Condition Gross amounts recognized Gross amounts offset on the Consolidated Statements of Financial Condition (a) Net amounts included on the Consolidated Statements of Financial Condition Financial instruments Cash Collateral pledged (b) Net amounts (dollars in thousands) As of December 31, 2017 Receivable on derivative contracts, at fair value $ 69,177 $ — $ 69,177 $ — $ 10,948 $ 58,229 Payable for derivative contracts, at fair value 42,750 — 42,750 — 1,031 41,719 As of December 31, 2016 Receivable on derivative contracts, at fair value 22,901 — 22,901 — 1,382 21,519 Payable for derivative contracts, at fair value 20,762 — 20,762 — 181 20,581 (a) Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred. (b) Includes the amount of collateral held or posted.
Schedule Equity Method Investments	The following table summarizes equity method investments held by the Company: As of December 31, 2017 2016 (dollars in thousands) Surf House Ocean Views Holdings, LLC $ 14,179 $ 13,522 Starboard Value LP 13,202 12,501 RCG Longview Debt Fund V Partners, LLC 9,284 7,256 RCG Longview Management, LLC 1,149 656 HealthCare Royalty GP, LLC 281 583 HealthCare Royalty GP II, LLC 148 354 RCG Longview Debt Fund IV Management, LLC 331 331 HealthCare Royalty GP III, LLC 764 208 RCG Kennedy House, LLC 154 183 RCG Longview Equity Management, LLC 114 114 RCG LPP II GP, LLC 487 — RCG Park Liberty GP Member Manager, LLC 428 141 Other 578 1,142 $ 41,099 $ 36,991 For the period ended December 31, 2017 , three equity method investments have met the significance criteria as defined under Regulation S-X Rule 4-08(g) of the SEC guidance. As such, the Company is presenting the following summarized financial information for the significant investees for the years ended December 31, 2017 , 2016, and 2015, and such information is as follows: As of December 31, 2017 2016 (dollars in thousands) Assets Cash $ 6,046 $ 5,766 Performance & management fee receivable 110,064 48,145 Investments in Portfolio Funds, at fair value 11,251 7,493 Other assets 1,060 1,122 Liabilities 74,256 21,250 Equity $ 54,165 $ 41,276 Year Ended December 31, 2017 2016 2015 (dollars in thousands) Revenues $ 132,862 $ 87,371 $ 35,268 Expenses (32,354 ) (34,490 ) (20,658 ) Net realized and unrealized gains (losses) 9,264 9,383 4,259 Net Income $ 109,772 $ 62,264 $ 18,869 For the period ended December 31, 2017 , equity method investments held by the Company in aggregate have met the significance criteria as defined under SEC guidance. As such, the Company is required to present summarized financial information for these significant investees for the years ended December 31, 2017 , 2016 and 2015, and such information is as follows: As of December 31, 2017 2016 (dollars in thousands) Assets $ 155,936 $ 88,965 Liabilities 74,316 22,504 Equity $ 81,620 $ 66,461 Year Ended December 31, 2017 2016 2015 (dollars in thousands) Revenues $ 137,052 $ 90,337 $ 38,571 Expenses (32,354 ) (34,490 ) (20,658 ) Net realized and unrealized gains (losses) 10,149 (6,305 ) 9,715 Net Income $ 114,847 $ 49,542 $ 27,628
Schedule of Securities Sold, Not yet Purchased	As of December 31, 2017 and 2016 , securities sold, not yet purchased, at fair value consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Common stocks $ 342,328 $ 263,460 Corporate bonds (a) 122 2,591 Preferred stock 77 — Warrants and rights — 39 $ 342,527 $ 266,090 (a) As of December 31, 2017 , the maturities ranged from July 2025 to January 2036 with interest rates ranged from 3.78% to 5.55% . As of December 31, 2016 , the maturities ranged from April 2021 to January 2036 with interest rates ranged from 5.50% to 6.25% .
Schedule of Assets and Associated Liabilities Accounted for as Secured Borrowings	The following tables present the contractual gross and net securities borrowing and lending agreements and the related offsetting amount, as of December 31, 2017 . Gross amounts not offset on the Consolidated Statements of Financial Condition Gross amounts recognized Gross amounts offset on the Consolidated Statements of Financial Condition (a) Net amounts included on the Consolidated Statements of Financial Condition Additional Amounts Available Financial instruments Cash Collateral pledged (b) Net amounts (dollars in thousands) As of December 31, 2017 Securities borrowed $ 443,148 $ — $ 443,148 $ — $ 414,778 $ — $ 28,370 Securities loaned 456,831 — 456,831 — 439,228 — 17,603 (a) Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred. (b) Includes the amount of cash collateral held/posted.
Investments Classified by Contractual Maturity Date	The following tables present gross obligations for securities loaned transactions by remaining contractual maturity and class of collateral pledged as of December 31, 2017 : Open and Overnight Up to 30 days 31 - 90 days Greater than 90 days Total (dollars in thousands) As of December 31, 2017 Equities $ 456,831 $ — $ — $ — $ 456,831
Fair Value, Concentration of Risk	Investment's percentage of the Company's equity at December 31, 2017 Issuer Security Type Country Industry Percentage of Equity Market Value (dollars in thousands) Linkem Equity Italy Wireless Broadband 7.52 % $ 56,271
Schedule of Other Investments	As of December 31, 2017 and 2016 , other investments included the following: As of December 31, 2017 2016 (dollars in thousands) Portfolio Funds, at fair value (1) $ 100,148 $ 120,023 Equity method investments (2) 41,099 36,991 Lehman claims, at fair value 301 265 $ 141,548 $ 157,279
Schedule of Other Investments, Portfolio Funds	The Portfolio Funds, at fair value as of December 31, 2017 and 2016 , included the following: As of December 31, 2017 2016 (dollars in thousands) Starboard Value and Opportunity Fund LP (c)(*) $ 32,079 $ 27,424 Formation8 Partners Fund I, L.P. (f) 28,243 22,234 RCG Longview Debt Fund V, L.P. (i)(*) 8,892 16,187 HealthCare Royalty Partners LP (a)(*) 3,452 7,147 Eclipse Ventures Fund I, L.P. (g) 3,428 1,790 Lagunita Biosciences, LLC (n) 2,400 1,698 RCG LPP2 PNW5 Co-Invest, L.P. (j)(*) 3,493 3,152 Starboard Leaders Fund LP (e)(*) 1,276 1,231 HealthCare Royalty Partners II LP (a)(*) 873 2,091 Quadratic Fund LLC (k) (*) 906 6,729 RCGL 12E13th LLC (i)(*) 237 348 RCG Park Liberty GP Member LLC (i) (*) 750 598 RCG Longview Debt Fund VI, LP (i) (*) 1,022 — Green Energy Metals Fund, LP (h) — 6,241 Starboard Partners Fund LP (d)(*) — 5,067 Orchard Square Partners Credit Fund LP (b) — 4,327 Other private investment (l)(*) 10,133 8,548 Other affiliated funds (m)(*) 2,964 5,211 $ 100,148 $ 120,023 * These portfolio funds are affiliates of the Company. The Company has no unfunded commitments regarding the portfolio funds held by the Company except as noted in Note 22 . (a) HealthCare Royalty Partners, L.P. and HealthCare Royalty Partners II, L.P. are private equity funds and therefore distributions will be made when cash flows are received from the underlying investments, typically on a quarterly basis. (b) Orchard Square Partners Credit Fund LP had a quarterly redemption policy with a 60 day notice period and a 4% penalty on redemptions of investments of less than a year in duration. (c) Starboard Value and Opportunity Fund LP permits quarterly withdrawals upon 90 days' notice. (d) Starboard Partners Fund LP permitted redemptions on a semi-annual basis on 180 days' prior written notice subsequent to an initial two year lock up. (e) Starboard Leaders Fund LP does not permit withdrawals, but instead allows terminations with respect to capital commitments upon 30 days' prior written notice at any time following the first anniversary of an investors' initial capital contribution. (f) Formation8 Partners Fund I, L.P. is a private equity fund which invests in early stage and growth transformational information and energy technology companies. Distributions will be made when the underlying investments are liquidated. (g) Eclipse Ventures Fund I, L.P. is a private equity fund which invests in early stage and growth hardware companies. Distributions will be made when the underlying investments are liquidated. (h) The Green Energy Metals Fund, LP invested the vast majority of its capital in physical off-exchange traded minor metals that are crucial to the production and sustainability of clean energy, emerging technology and energy efficiency. The Company was invested in a managed account specifically targeting cobalt. The Green Energy Metals Fund, LP is a private equity structure and therefore distributions were made when the underlying investments were liquidated. (i) RCGL 12E13th LLC, RCG Longview Debt Fund V, L.P., RCG Park Liberty GP Member LLC, and RCG Longview Debt Fund VI, LP are real estate private equity structures and therefore distributions will be made when the underlying investments are liquidated. (j) RCG LPP2 PNW5 Co-Invest, L.P. is a single purpose entity formed to participate in a joint venture which acquired five multi-unit residential rental properties located in the Pacific Northwest. RCG LPP2 PNW5 Co-Invest, L.P. is a private equity structure and therefore distributions will be made when the underlying investments are liquidated. (k) Quadratic Fund LLC permits redemptions 30 days prior written notice. (l) Other private investment represents the Company's closed end investment in a portfolio fund that invests in a wireless broadband communication provider in Italy. (m) The majority of these funds are affiliates of the Company or are managed by the Company and the investors can redeem from these funds as investments are liquidated. (n) Lagunita Biosciences, LLC, a healthcare investment company that creates and grows early stage companies to commercialize impactful translational science that addresses significant clinical needs, is a private equity structure and therefore distributions will be made when the underlying investments are liquidated.
Consolidated Funds
Investment Holdings [Line Items]
Marketable Securities	As of December 31, 2017 and 2016 , securities owned, at fair value, held by the Consolidated Funds consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Preferred stock $ 50,445 $ 37,343 Common stocks 77,702 28,474 U.S. Government securities (a) 34,201 6,994 Corporate bonds (b) — 4,214 Term Loan — 2,209 Warrants and rights 3,568 3 $ 165,916 $ 79,237 (a) As of December 31, 2017 , maturities ranged from January 2018 2017 to April 2022 and interest rates ranged from 0% to 5.75% . As of December 31, 2016 , the maturity was March 2017 with an interest rate of 0% . (b) As of December 31, 2016 , maturities ranged from October 2017 to June 2038 and interest rates ranged from 0% and 14.37% .
Schedule of Derivative Instruments	Receivable on derivative contracts As of December 31, 2017 and 2016 , receivable on derivative contracts, at fair value, held by the Consolidated Funds are comprised of: As of December 31, 2017 2016 (dollars in thousands) Currency forwards $ 524 $ 18 Equity swaps 1,754 731 Options 242 144 $ 2,520 $ 893 Payable for derivative contracts As of December 31, 2017 and 2016 , payable for derivative contracts, at fair value, held by the Consolidated Funds are comprised of: As of December 31, 2017 2016 (dollars in thousands) Currency forwards $ 11 $ 10 Equity swaps 7,042 495 Options 77 67 $ 7,130 $ 572
Schedule of Securities Sold, Not yet Purchased	As of December 31, 2017 , there were no securities sold, not yet purchased, at fair value. As of December 31, 2016 , securities sold, not yet purchased, at fair value, held by the Consolidated Funds consisted of the following: As of December 31, 2016 (dollars in thousands) Corporate bonds (a) $ 672 Common stocks 211 $ 883 (a) As of December 31, 2016 , maturities ranged from September 2019 to September 2023 and interest rates ranged from 4.38% to 9.25% .
Schedule of Other Investments, Portfolio Funds	Investments in Portfolio Funds, at fair value As of December 31, 2017 and 2016 , investments in Portfolio Funds, at fair value, included the following: As of December 31, 2017 2016 (dollars in thousands) Investments of Enterprise LP $ 87,221 $ 114,159 Investments of Merger Fund 286,890 281,572 Investments of Caerus LP — 5,734 $ 374,111 $ 401,465
Enterprise Master
Investment Holdings [Line Items]
Marketable Securities	Securities owned by Enterprise Master, at fair value As of December 31, 2017 2016 (dollars in thousands) Preferred stock $ — $ 1,581 Common stock 608 835 $ 608 $ 2,416
Schedule of Other Investments, Portfolio Funds	Portfolio Funds, owned by Enterprise Master, at fair value As of December 31, 2017 2016 Strategy (dollars in thousands) RCG Special Opportunities Fund, Ltd* Multi-Strategy $ 97,345 $ 101,832 RCG Longview Equity Fund, LP* Real Estate 1,266 4,744 RCG Longview Debt Fund IV, LP* Real Estate 99 1,637 RCG Longview II, LP* Real Estate 229 836 RCG Renergys, LLC* Energy — 1 Other Private Investments Various 937 8,682 Other Real Estate Investments * Real Estate — 295 $ 99,876 $ 118,027 * Affiliates of the Company.
Merger Master
Investment Holdings [Line Items]
Schedule of Derivative Instruments	Receivable on derivative contracts, at fair value, owned by Merger Master As of December 31, 2017 2016 Description (dollars in thousands) Options $ 108,063 $ 4,264 Equity swaps 14,488 255 $ 122,551 $ 4,519 Payable for derivative contracts, at fair value, owned by Merger Master As of December 31, 2017 2016 Description (dollars in thousands) Options $ 1,256 $ 2,285 Currency forwards 213 — Equity swaps 1,249 123 $ 2,718 $ 2,408

Fair Value Measurements for O44

Fair Value Measurements for Operating Entities and Consolidated Funds (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following table presents the assets and liabilities that are measured at fair value on a recurring basis on the accompanying consolidated statements of financial condition by caption and by level within the valuation hierarchy as of December 31, 2017 and 2016 : Assets at Fair Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities owned US Government securities $ 2,807 $ — $ — $ 2,807 Preferred stock 571 918 8,115 9,604 Common stocks 627,011 5,484 7,570 640,065 Convertible bonds — — 282 282 Corporate bonds — 4,909 — 4,909 Trade claims — — 5,950 5,950 Warrants and rights 7,087 — 2,517 9,604 Receivable on derivative contracts, at fair value Futures 58 — — 58 Currency forwards — 5 — 5 Swaps — 10,942 — 10,942 Options 56,717 — 1,455 58,172 Other investments Lehman claim — — 301 301 Consolidated Funds Securities owned US Government securities 30,552 3,649 — 34,201 Preferred stock — — 50,445 50,445 Common stocks 77,652 — 50 77,702 Warrants and rights — — 3,568 3,568 Receivable on derivative contracts, at fair value Currency forwards — 524 — 524 Equity swaps — 1,754 — 1,754 Options 242 — — 242 $ 802,697 $ 28,185 $ 80,253 $ 911,135 Percentage of total assets measured at fair value on a recurring basis 88.1 % 3.1 % 8.8 % Portfolio funds measured at net asset value (a) 100,148 Consolidated funds' portfolio funds measured at net asset value (a) 374,111 Equity method investments 41,099 Total investments $ 1,426,493 Liabilities at Fair Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities sold, not yet purchased Common stocks $ 342,328 $ — $ — $ 342,328 Corporate bonds — 122 — 122 Preferred stock 77 — — 77 Warrants and rights — — — — Payable for derivative contracts, at fair value Futures 242 — — 242 Currency forwards — 874 — 874 Swaps — 71 — 71 Options 19,162 — 22,401 41,563 Accounts payable, accrued expenses and other liabilities Contingent consideration liability (b) — — 3,440 3,440 Consolidated Funds Payable for derivative contracts, at fair value Currency forwards — 11 — 11 Options 77 — — 77 Equity swaps — 7,042 — 7,042 $ 361,886 $ 8,120 $ 25,841 $ 395,847 Percentage of total liabilities measured at fair value 91.4 % 2.1 % 6.5 % (a) In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition. (b) In accordance with the terms of the purchase agreements for acquisitions that closed during the third and fourth quarter of 2015 and the second quarter of 2016, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, December 2020, and June 2018, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2017 can range from $0.1 million to $15.0 million . Assets at Fair Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities owned US Government securities $ 3,780 $ — $ — $ 3,780 Preferred stock — — 15,811 15,811 Common stocks 658,179 1,355 10,121 669,655 Convertible bonds — — 250 250 Corporate bonds — 2,477 — 2,477 Trade claims — — 562 562 Warrants and rights 4,616 — 3,719 8,335 Mutual funds 6 — — 6 Receivable on derivative contracts, at fair value Futures 104 — — 104 Currency forwards — 592 — 592 Swaps — 468 — 468 Options 6,662 322 14,753 21,737 Other investments Lehman claim — — 265 265 Consolidated Funds Securities owned US Government securities 6,994 — — 6,994 Preferred stock — 415 36,928 37,343 Common stocks 19,467 8,712 295 28,474 Corporate bonds — 4,214 — 4,214 Warrants and rights — — 3 3 Term loan — 1,552 657 2,209 Receivable on derivative contracts, at fair value Currency forwards — 18 — 18 Equity swaps — 731 — 731 Options 132 12 — 144 $ 699,940 $ 20,868 $ 83,364 $ 804,172 Percentage of total assets measured at fair value on a recurring basis 87.0 % 2.6 % 10.4 % Portfolio funds measured at net asset value (a) 120,023 Consolidated funds' portfolio funds measured at net asset value (a) 401,465 Equity method investments 36,991 Total investments $ 1,362,651 Liabilities at Fair Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Operating Entities Securities sold, not yet purchased Common stocks $ 263,460 $ — $ — $ 263,460 Corporate bonds — 2,591 — 2,591 Warrants and rights 39 — — 39 Payable for derivative contracts, at fair value Futures 642 — — 642 Swaps — 181 — 181 Options 5,186 — 14,753 19,939 Accounts payable, accrued expenses and other liabilities Contingent consideration liability (b) — — 5,997 5,997 Consolidated Funds Securities sold, not yet purchased Common stocks 211 — — 211 Corporate bonds — 672 — 672 Payable for derivative contracts, at fair value Currency forwards — 10 — 10 Options 67 — — 67 Equity swaps — 495 — 495 $ 269,605 $ 3,949 $ 20,750 $ 294,304 Percentage of total liabilities measured at fair value 91.6 % 1.3 % 7.1 % (a) In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition. (b) In accordance with the terms of the purchase agreements for acquisitions that closed during 2012 and the third and fourth quarter of 2015, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, and December 2020, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2016 can range from $0.1 million to $15.1 million .
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	The following table includes a roll forward of the amounts for the year ended December 31, 2017 and 2016 for financial instruments classified within level 3. The classification of a financial instrument within level 3 is based upon the significance of the unobservable inputs to the overall fair value measurement. Year Ended December 31, 2017 Balance at December 31, 2016 Transfers in Transfers out Purchases/(covers) (Sales)/shorts Realized and Unrealized gains/losses Balance at December 31, 2017 Change in unrealized gains/losses relating to instruments still held (1) (dollars in thousands) Operating Entities Preferred stock $ 15,811 $ — $ (25,098 ) (a) (f) $ 25,785 $ (2,956 ) $ (5,427 ) $ 8,115 $ 486 Common stocks 10,121 — — 2,670 (2,688 ) (2,533 ) 7,570 (412 ) Convertible bonds 250 — — 282 — (250 ) 282 — Options, asset 14,753 — — — — (13,298 ) 1,455 (13,298 ) Options, liability 14,753 — — — — 7,648 22,401 7,648 Warrants and rights 3,719 2,173 (b) (d) — — (4,118 ) 743 2,517 510 Trade claims 562 — — 5,865 (611 ) 134 5,950 202 Lehman claim 265 — — — — 36 301 36 Contingent consideration liability 5,997 — — — (392 ) (2,165 ) 3,440 (2,165 ) Consolidated Funds Preferred stock 36,928 22,644 (f) (13,668 ) (a) 8,437 (11,903 ) 8,007 50,445 3,896 Common stocks 295 — — 526 (848 ) 77 50 — Warrants and rights 3 — — — — 3,565 3,568 3,565 Term Loan 657 — — 202 (1,021 ) 162 — — Year Ended December 31, 2016 Balance at December 31, 2015 Transfers in Transfers out Purchases/(covers) (Sales)/shorts Realized and Unrealized gains/losses Balance at December 31, 2016 Change in unrealized gains/losses relating to instruments still held (1) (dollars in thousands) Operating Entities Preferred stock $ 12,872 $ — $ (1,000 ) (a) $ 3,717 $ (218 ) $ 440 $ 15,811 $ 34 Common stocks 2,278 — — 7,099 (3,222 ) 3,966 10,121 3,972 Convertible bonds 819 — — — (569 ) — 250 — Options, asset 18,194 — — — — (3,441 ) 14,753 (3,441 ) Options, liability 18,194 — — — — (3,441 ) 14,753 (3,441 ) Warrants and rights 2,572 — — 1,914 (817 ) 50 3,719 79 Trade Claims — 675 (e) — 289 (325 ) (77 ) 562 (111 ) Lehman claim 299 — — — — (34 ) 265 (35 ) Contingent consideration liability 6,158 — — 2,397 (4,697 ) 2,139 5,997 — Consolidated Funds Preferred stock 32,000 — (11,000 ) (a) 13,483 — 2,445 36,928 2,445 Common Stock — — — 314 — (19 ) 295 (19 ) Warrants and rights — — — — — 3 3 3 Term Loan — — — 590 — 67 657 67 (1) Unrealized gains/losses are reported in other income (loss) in the accompanying consolidated statements of operations. (a) The investments were converted to common stock. (b) The Company received warrants as part of a transaction. (c) The entity in which the Company is invested completed an initial public offering. (d) As part of the preferred stock sale, the sellers received contingent value rights to be paid in the event certain milestones are reached. (e) The investment undertook a reorganization and subsequently is not traded in an active market. (f) The Company transferred investments to a consolidated fund.
Fair Value Inputs, Assets, Quantitative Information	The following table includes quantitative information as of December 31, 2017 and 2016 for financial instruments classified within level 3. The table below quantifies information about the significant unobservable inputs used in the fair value measurement of the Company's level 3 financial instruments. Quantitative Information about Level 3 Fair Value Measurements Fair Value at December 31, 2017 Valuation techniques Unobservable Inputs Range Level 3 Assets (dollars in thousands) Common and preferred stocks $ 5,642 Guideline companies/transaction price Market multiples 4.8x to 8.5x Trade claims 70 Discounted cash flows Discount rate 20% Warrants and rights 2,516 Model based Discounted cash flows Volatility Discount rate 61% 22% Options 1,455 Option pricing models Volatility 28% Other level 3 assets (a) 70,570 Total level 3 assets 80,253 Level 3 Liabilities Options 22,401 Option pricing models Volatility 28% Contingent consideration liability 3,440 Discounted cash flows Projected cash flow and discount rate 8% - 23% (weighted average 22%) Total level 3 liabilities $ 25,841 Quantitative Information about Level 3 Fair Value Measurements Fair Value at December 31, 2016 Valuation techniques Unobservable Inputs Range Level 3 Assets (dollars in thousands) Common and preferred stocks $ 10,917 Guideline companies/transaction price Option pricing method, discounted cash flow Volatility Market multiples Discount rate 37% 0.8x to 9.3x 9.5% to 10% Trade claims 520 Discounted cash flows Market multiples Discount rate 6x 20% Warrants and rights 3,719 Model based Volatility 30% to 85% (weighted average 73%) Options 14,753 Option pricing models Volatility 40% Other level 3 assets (a) 53,455 Total level 3 assets 83,364 Level 3 Liabilities Options 14,753 Option pricing models Volatility 40% Contingent consideration liability 5,997 Discounted cash flows Projected cash flow and discount rate 8% - 25% Total level 3 liabilities $ 20,750 (a) The quantitative disclosures exclude financial instruments for which the determination of fair value is based on prices from recent transactions.
Fair Value Measurements, Nonrecurring	The following table presents the carrying values and fair values, at December 31, 2017 and 2016 , of financial assets and liabilities and information on their classification within the fair value hierarchy which are not measured at fair value on a recurring basis. For additional information regarding the financial instruments within the scope of this disclosure, and the methods and significant assumptions used to estimate their fair value see Note 3 . December 31, 2017 December 31, 2016 Fair Value Hierarchy Carrying Amount Fair Value Carrying Amount Fair Value (dollars in thousands) Financial Assets Operating companies Cash and cash equivalents $ 130,052 $ 130,052 $ 110,990 $ 110,990 Level 1 Cash collateral pledged 17,888 17,888 13,342 13,342 Level 2 Segregated cash 116,268 116,268 1,024 1,024 Level 1 Securities borrowed 443,148 414,763 — — Level 2 Loans receivable 37,993 37,993 (d) 31,088 31,088 (d) Level 3 Consolidated funds Cash and cash equivalents 21,988 21,988 17,761 17,761 Level 1 Financial Liabilities Securities loaned 456,831 440,162 — — Level 2 Convertible debt 141,502 (a) 172,709 (b) 130,029 (a) 149,545 (b) Level 2 Notes payable and other debt 173,458 182,352 (c) 77,030 80,817 (c) Level 2 (a) The carrying amount of the convertible debt includes an unamortized discount of $25.6 million and $17.8 million as of December 31, 2017 and 2016 , respectively. (b) The convertible debt includes the conversion option and is based on the last broker quote available. (c) Notes payable and other debt are based on the last broker quote available. (d) The fair market value of level 3 loans is calculated using discounted cash flows.

Receivables from and payables45

Receivables from and payables to brokers, dealers and clearing organizations receivables from brokers, dealers, and clearing organization (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables from Brokers-Dealers and Clearing Organizations [Abstract]
Schedule of Due to (from) Broker-Dealers and Clearing Organizations [Table Text Block]	As of December 31, 2017 and 2016 , amounts receivable from brokers, dealers and clearing organizations include: As of December 31, 2017 2016 (dollars in thousands) Broker-dealers $ 409,499 $ 78,898 Securities failed to deliver 87,820 — Clearing organizations 6,126 — Stock borrow interest receivable 4,733 — $ 508,178 $ 78,898 As of December 31, 2017 and 2016 , amounts payable to brokers, dealers and clearing organizations include: As of December 31, 2017 2016 (dollars in thousands) Broker-dealers $ 145,860 $ 210,309 Securities failed to receive 53,540 — Clearing organizations 48,257 — Stock loan interest payable 4,496 — $ 252,153 $ 210,309

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Fixed Assets	As of December 31, 2017 and 2016 , fixed assets consisted of the following: As of December 31, 2017 2016 (dollars in thousands) Telephone and computer equipment $ 3,465 $ 2,787 Computer software 2,914 2,167 Furniture and fixtures 1,423 1,204 Leasehold improvements 36,702 35,092 Assets acquired under capital leases—equipment 6,920 4,075 Aircraft and related equipment 17,369 20,893 Other 58 57 68,851 66,275 Less: Accumulated depreciation and amortization (28,355 ) (23,867 ) $ 40,496 $ 42,408

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill Disclosure	The following table presents the changes in the Company's goodwill balance, by reporting unit for the years ended December 31, 2017 , 2016 , and 2015 : Investment Management Broker- Total (dollars in thousands) Beginning balance - December 31, 2015 Goodwill $ 30,228 $ 47,818 $ 78,046 Accumulated impairment charges (10,200 ) (9,485 ) (19,685 ) Net 20,028 38,333 58,361 Activity: 2016 Recognized goodwill — 3,519 3,519 Goodwill allocated to disposal group (1,202 ) — (1,202 ) Goodwill impairment charges — — — Ending balance: December 31, 2016 Goodwill 29,026 51,337 80,363 Accumulated impairment charges (10,200 ) (9,485 ) (19,685 ) Net 18,826 41,852 60,678 Activity: 2017 Recognized goodwill — — — Goodwill allocated to disposal group — — — Goodwill impairment charges — — — Ending balance: December 31, 2017 Goodwill 29,026 51,337 80,363 Accumulated impairment charges (10,200 ) (9,485 ) (19,685 ) Net $ 18,826 $ 41,852 $ 60,678
Intangible Assets Disclosure	Information for the Company's intangible assets that are subject to amortization is presented below as of December 31, 2017 and 2016 . December 31, 2017 December 31, 2016 Amortization Period Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount (in years) (in thousands) (in thousands) Trade names 0.6 - 7.5 $ 10,622 $ (10,555 ) $ 67 $ 9,962 $ (9,689 ) $ 273 Customer relationships 3 - 14 41,134 (15,733 ) 25,401 33,874 (12,948 ) 20,926 Customer contracts 1.2 800 (800 ) — 800 (800 ) — Non compete agreements and covenants with limiting conditions acquired 3 - 5 2,237 (1,479 ) 758 2,268 (818 ) 1,450 Intellectual property 3 - 10 8,243 (4,514 ) 3,729 8,283 (5,163 ) 3,120 $ 63,036 $ (33,081 ) $ 29,955 $ 55,187 $ (29,418 ) $ 25,769
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The estimated future amortization expense for the Company's intangible assets as of December 31, 2017 is as follows: (dollars in thousands) 2018 $ 4,946 2019 4,168 2020 3,950 2021 3,890 2022 3,108 Thereafter 9,893 $ 29,955

Other Assets (Tables)

Other Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Other Assets [Abstract]
Schedule of Other Assets	Other assets in Operating Entities are as follows: As of December 31, 2017 2016 (dollars in thousands) Prepaid expenses $ 13,267 $ 10,669 Deposits 877 5,322 Reinsurance receivables, net (d) 14,014 5,187 Loan receivable (a) — 3,700 Tax receivables 1,457 3,267 Redemption Receivable 19,565 — Interest and dividends receivable 1,021 718 Deferred acquisition costs (c) 1,978 677 Deferred rent asset — 52 Military loan (b) 19,851 4,476 Other 16,238 4,338 $ 88,268 $ 38,406 (a) As of December 31, 2016, the maturity was August 2017 with interest rate of 12% . (b) As of December 31, 2017, the maturity is January 2024, with interest rate of 8% for the first five years and 8.5% for the remainder of the term, related to the Company's commercial reinsurance activities. As of December 31, 2016, the maturity is January 2024, with interest rate of 8% for the first five years and 8.5% for the remainder of the term, related to the Company's commercial reinsurance activities. (c) Balances relate to the Company's reinsurance business entered into during 2016 (See Note 17 ).

Accounts Payable Accrued Expe49

Accounts Payable Accrued Expenses and Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Accounts Payable, Accrued Expenses and Other Liabilities [Abstract]
Schedule of Accounts Payable and Accrued Liabilities	Accounts payable, accrued expenses and other liabilities in Operating Entities are as follows: As of December 31, 2017 2016 (dollars in thousands) Deferred rent obligations (see Note 3(k)) $ 12,822 $ 10,335 Contingent consideration payable (see Note 2) 3,440 5,997 Equity in RCG Longview Partners II, LLC (see Note 5a(3)) 6,022 5,948 Interest and dividends payable 2,891 3,541 Loss reserves and claims incurred but not reported (a) 9,464 3,455 Professional fees payable 5,008 3,143 Unearned premiums (a) 6,116 2,375 Fees payable 798 1,093 Accrued tax liabilities 7,482 456 Litigation reserve 3,000 — Accrued expenses and accounts payable (b) 39,490 11,182 $ 96,533 $ 47,525 (a) Balances relate to the Company's reinsurance business entered into during 2016 (See Note 17 ). (b) As of December 31, 2017, the balance includes premiums accrued but not yet paid of $18.0 million related to the Company’s reinsurance business.

Redeemable Non-Controlling In50

Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds (Tables)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Redeemable non-controlling interests in consolidated subsidiaries and funds	Redeemable non-controlling interests in consolidated subsidiaries and funds and the related net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds are comprised as follows: As of December 31, 2017 As of December 31, 2016 (dollars in thousands) Redeemable non-controlling interests in consolidated subsidiaries and funds Operating companies $ 6,113 $ 7,638 Consolidated Funds 434,491 371,567 $ 440,604 $ 379,205
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	Year Ended December 31, 2017 2016 2015 (dollars in thousands) Income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds Operating companies $ 2,353 $ 3,717 $ 9,503 Consolidated Funds 21,438 3,165 5,743 $ 23,791 $ 6,882 $ 15,246

Share-Based Compensation and 51

Share-Based Compensation and Employee Ownership Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes the Company's stock option activity for the years ended December 31, 2017 and 2016: Class A Common Shares Subject Weighted Average Weighted Average Aggregate Intrinsic (in years) (dollars in thousands) Balance outstanding at December 31, 2015 4,167 $ 19.56 1.6 $ 87 Options granted — — — — Options exercised — — — — Options expired — — — — Balance outstanding at December 31, 2016 4,167 $ 19.56 0.10 $ — Options granted — — — — Options exercised — — — — Options expired (4,167 ) 19.56 — — Balance outstanding at December 31, 2017 — $ — 0 $ — Options exercisable at December 31, 2016 4,167 $ 19.56 0.10 $ — Options exercisable at December 31, 2017 — $ — 0 $ — (1) Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016 .
Schedule of Share-based Compensation, Stock Appreciation Rights, Activity	As of December 31, 2017 , the Company's stock options were fully expensed. The following table summarizes the Company's SAR's for the years ended December 31, 2017 : Class A Common Shares Subject Weighted Average Weighted Average Aggregate Intrinsic (in years) (dollars in thousands) Balance outstanding at December 31, 2015 100,000 $ 11.60 2.21 $ 558 SAR's granted — — — — SAR's acquired — — — — SAR's expired — — — — Balance outstanding at December 31, 2016 100,000 $ 11.60 1.21 $ 435 SAR's granted — — — — SAR's vested (25,000 ) 11.60 — — SAR's expired — — — — Balance outstanding at December 31, 2017 75,000 $ 11.60 0.21 $ 173 SAR's exercisable at December 31, 2016 — $ — — $ — SAR's exercisable at December 31, 2017 — $ — 0 $ — (1) Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016 .
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity	Restricted shares and restricted stock units are referred to collectively as restricted stock. The following table summarizes the Company's restricted share and restricted stock unit activity for the years ended December 31, 2017 and 2016: Nonvested Restricted Class A Common Shares and Class A Common Restricted Stock Units Weighted-Average Balance outstanding at December 31, 2015 5,370,091 $ 16.68 Granted 2,157,403 14.02 Vested (1,487,092 ) 14.95 Canceled — — Forfeited (322,470 ) 14.89 Balance outstanding at December 31, 2016 5,717,932 $ 16.23 Granted 2,255,441 14.98 Vested (2,036,366 ) 14.64 Canceled — — Forfeited (357,714 ) 15.77 Balance outstanding at December 31, 2017 5,579,293 $ 16.33 Included in the restricted share and restricted stock unit activity are performance linked restricted stock units of 481,438 which were awarded to employees of the Company in December 2013 and January 2014. An additional 700,000 performance linked restricted stock units were awarded in March 2016. Of the awards granted, 109,375 have been forfeited through December 31, 2017 . The remaining awards, included in the outstanding balance as of December 31, 2017 , will vest between March 2019 and December 2020 and will be earned only to the extent that the Company attains specified market conditions relating to its volume-weighted average share price and total shareholder return in relation to certain benchmark indices and performance goals relating to aggregate net income and average return on shareholder equity. The actual number of RSUs ultimately earned could vary from zero , if performance goals are not met, to as much as 150% of the targeted award. Each RSU is equal to the one share of the Company’s Class A common stock. Compensation expense is recognized to the extent that it is probable that the Company will attain the performance goals.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of the Company's income tax expense for the years ended December 31, 2017 , 2016 and 2015 are as follows: Year ended December 31, 2017 2016 2015 (dollars in thousands) Current tax expense/(benefit) Federal $ 421 $ 1,268 $ (635 ) State and local 2,034 1,972 313 Foreign 428 262 348 Total $ 2,883 $ 3,502 $ 26 Deferred tax expense/(benefit) Federal $ 44,071 $ (22,834 ) $ (37,979 ) State and local (2,938 ) (1,900 ) (7,420 ) Foreign 37 2,140 (2,123 ) Total 41,170 (22,594 ) (47,522 ) Total Tax expense/(benefit) $ 44,053 $ (19,092 ) $ (47,496 )
Schedule of Effective Income Tax Rate Reconciliation	The reconciliations of the Company's federal statutory rate to the effective income tax rate for the years ended December 31, 2017 , 2016 , and 2015 are as follows: Year ended December 31, 2017 2016 2015 Pre-tax loss at U.S. statutory rate 35.0 % 35.0 % 35.0 % Dividend received deduction (25.9 ) — — Bargain purchase gain (34.8 ) — — Basis adjustment on investments 65.2 — — Nondeductible expenses 14.2 — — Deferred asset recognition — — (323.8 ) Unrecognized gains on foreign subsidiaries — 38.7 — Change in valuation allowance — (6.7 ) — Impact of tax law change 669.8 — (27.9 ) State and foreign tax 25.3 1.3 (39.6 ) Reversal of income attributable to redeemable non-controlling interests (119.6 ) 1.3 (46.5 ) Other, net 3.7 (9.0 ) (11.0 ) Total 632.9 % 60.6 % (413.8 )%
Schedule of Deferred Tax Assets and Liabilities	The components of the Company's deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows: As of December 31, 2017 2016 (dollars in thousands) Deferred tax assets, net of valuation allowance Net operating loss $ 78,650 $ 126,037 Deferred compensation 39,992 44,966 Goodwill 1,042 4,758 Option liability 5,776 — Fixed assets — 3,541 Tax credits 4,419 2,898 Acquired lease liability 3,473 4,111 Other 2,696 2,238 Total deferred tax assets 136,048 188,549 Valuation allowance (2,103 ) (2,119 ) Deferred tax assets, net of valuation allowance 133,945 186,430 Deferred tax liabilities Unrealized gains on investments (7,523 ) (20,774 ) Amortization of bond discount (6,402 ) — Other (3,697 ) — Total deferred tax liabilities (17,622 ) (20,774 ) Deferred tax assets/(liabilities), net $ 116,323 $ 165,656
Summary of Operating Loss Carryforwards	The Company has the following net operating loss carryforwards at December 31, 2017 : Federal New York State New York City Hong Kong Jurisdiction: Net operating loss (in millions) $248.4 $93.4 $130.8 $12.8 Year of expiration 2036 2036 2036 Indefinite
Summary of Positions for which Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table Text Block]	The components of unrecognized tax benefits are as follows: As of December 31, 2017 2016 (dollars in thousands) Beginning balance at January 1 $ — $ — Increases due to acquisition 2,847 — Increases due to current year positions 1,100 — Ending balance at December 31 $ 3,947 $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Annual Lease and Service Payments	As of December 31, 2017 , future minimum annual lease and service payments for the Company were as follows: Equipment Leases (a) Service Payments Facility Leases (b) (dollars in thousands) 2018 $ 3,511 $ 21,631 $ 25,960 2019 1,599 10,987 21,453 2020 669 1,539 17,626 2021 639 337 17,592 2022 420 — 11,942 Thereafter — — 7,354 $ 6,838 $ 34,494 $ 101,927 (a) Equipment Leases include the Company's commitments relating to operating and capital leases. See Note 23 for further information on the capital lease minimum payments which are included in the table. (b) The Company has entered into various agreements to sublease certain of its premises. The Company recorded sublease income related to these leases of $1.1 million , $2.2 million , and $2.3 million and for the years ended December 31, 2017 , 2016 , and 2015 respectively.
Other Commitments	The following table summarizes unfunded commitments as of December 31, 2017 : Entity Unfunded Commitments Commitment term (dollars in millions) Real estate (a) $ 19.5 (a) HealthCare Royalty Partners funds (b) 6.2 2 years Eclipse Ventures Fund I, L.P. (formerly Formation8 Partners Hardware Fund I, L.P.) 0.4 7 years Lagunita Biosciences, LLC 2.0 3 years Eclipse Fund II, L.P. 0.9 8 years Eclipse Continuity Fund I, L.P. 0.6 9 years (a) The Company had unfunded commitments pertaining to capital commitments in six real estate investments held by the Company, all of which pertain to related party investments. Such commitments can be called at any time up to four years, subject to advance notice. (b) The Company is a limited partner of the HealthCare Royalty Partners funds (which are managed by Healthcare Royalty Management) and is a member of HealthCare Royalty Partners General Partners. The Company will make its pro-rata investment in the HealthCare Royalty Partners funds along with the other limited partners.

Convertible Debt and Notes Pa54

Convertible Debt and Notes Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Debt and Capital Lease Obligations	As of December 31, 2017 and 2016 , the Company's outstanding debt was as follows: As of December 31, 2017 2016 (dollars in thousands) Convertible debt $ 141,502 $ 130,029 Note payable 132,970 60,953 Term loan 28,121 — Other notes payable 8,247 14,237 Capital lease obligations 4,120 1,840 $ 314,960 $ 207,059
Schedule of Maturities of Debt and Future Minimum Lease Payments for Capital Leases	Annual scheduled maturities of debt and minimum payments (of principle and interest) for all debt outstanding as of December 31, 2017 , are as follows: Convertible Debt Note Payable Term loan Other Note Payable Capital Lease (dollars in thousands) 2018 $ 4,840 $ 10,340 $ — $ 2,032 $ 2,059 2019 38,925 10,143 28,901 3,410 717 2020 4,050 10,143 — 1,363 639 2021 4,050 10,143 — 2,512 639 2022 139,050 10,143 — — 420 Thereafter — 188,715 — — — Subtotal 190,915 239,627 28,901 9,317 4,474 Less (a) (49,413 ) (106,657 ) (780 ) (1,070 ) (354 ) Total $ 141,502 $ 132,970 $ 28,121 $ 8,247 $ 4,120 (a) Amount necessary to reduce net minimum payments to present value calculated at the Company's implicit rate at inception. This amount also includes capitalized debt costs and the unamortized discount on the convertible debt.
Schedule of Line of Credit Facilities	As of December 31, 2017 , the Company has eight irrevocable letters of credit, related to leased office space, for which there is cash collateral pledged and the Company pays a fee on the stated amount of the letter of credit. The Company also has pledged as collateral, $11.8 million , as of December 31, 2017 , and $5.5 million , as of December 31, 2016 , due between March 2018 and March 2021, for reinsurance agreements . Location Amount Maturity (dollars in thousands) Connecticut $ 65 January 2018 Boston $ 382 March 2018 New York $ 355 April 2018 New York $ 70 May 2018 New York $ 596 October 2018 New York $ 2,250 October 2018 New York $ 1,600 November 2018 San Francisco $ 710 January 2019

Stockholder's Equity (Tables)

Stockholder's Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Treasury Stock Activity	The following represents the activity relating to the treasury stock held by the Company during the year ended December 31, 2017 : Treasury stock shares Cost Average cost per share Balance outstanding at December 31, 2016 9,810,802 $ 153,845 $ 15.68 Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions 822,996 11,889 14.45 Shares of stock received in respect of indemnification claims 97,612 1,626 16.66 Purchase of treasury stock 1,401,866 19,486 13.90 Balance outstanding at December 31, 2017 12,133,276 $ 186,846 $ 15.40

Accumulated Other Comprehensi56

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income / (Loss) [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	Year Ended December 31, 2017 2016 2015 (dollars in thousands) Beginning Balance $ (2 ) $ — $ 17 Foreign currency translation (6 ) (2 ) (17 ) Ending Balance $ (8 ) $ (2 ) $ —

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share, Basic and Diluted	The computation of earnings per share is as follows: Year Ended December 31, 2017 2016 2015 (dollars in thousands, except share and per share data) Net income (loss) $ (37,091 ) $ (12,395 ) $ 58,975 Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds 23,791 6,882 15,246 Net income (loss) attributable to Cowen Inc. (60,882 ) (19,277 ) 43,729 Preferred stock dividends 6,792 6,792 4,075 Net income (loss) attributable to Cowen Inc. common stockholders $ (67,674 ) $ (26,069 ) $ 39,654 Shares for basic and diluted calculations: Weighted average shares used in basic computation 29,492 26,857 27,522 Stock options — — 3 Performance based restricted stock — — 65 Stock appreciation rights — — 35 Restricted stock — — 1,418 Weighted average shares used in diluted computation 29,492 26,857 29,043 Earnings (loss) per share: Basic $ (2.29 ) $ (0.97 ) $ 1.44 Diluted $ (2.29 ) $ (0.97 ) $ 1.37

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Reporting Information, by Segment	The following tables set forth operating results for the Company's investment management and broker-dealer segments and related adjustments necessary to reconcile the Company's Economic Income (Loss) measure to arrive at the Company's consolidated US GAAP net income (loss): Year Ended December 31, 2017 Adjustments Investment Broker-Dealer Total Economic Income/(Loss) Funds Consolidation Other Adjustments US GAAP (dollars in thousands) Revenues Investment banking $ — $ 223,614 $ 223,614 $ — $ — $ 223,614 Brokerage 38 312,742 312,780 — (19,170 ) (i) 293,610 Management fees 52,239 3,148 55,387 (2,593 ) (19,549 ) (a) 33,245 Incentive income (loss) 26,028 — 26,028 (1,739 ) (18,906 ) (a) 5,383 Investment income (loss) 31,447 13,695 45,142 — (45,142 ) (c)(f) — Interest and dividends — — — — 49,440 (c) 49,440 Reimbursement from affiliates — — — (297 ) 3,157 (e) 2,860 Aircraft lease revenue — — — — 3,751 (f) 3,751 Reinsurance premiums — — — — 30,996 (g) 30,996 Other revenue 1,575 1,656 3,231 — 5,330 (g) 8,561 Consolidated Funds revenues — — — 7,321 — 7,321 Total revenues 111,327 554,855 666,182 2,692 (10,093 ) 658,781 Expenses Non interest expense 92,567 532,820 625,387 (199 ) 58,935 (b)(d) 684,123 Interest and dividends 14,268 4,620 18,888 — 42,061 (c) 60,949 Consolidated Funds expenses — — — 12,526 — 12,526 Total expenses 106,835 537,440 644,275 12,327 100,996 757,598 Total other income (loss) — — — 31,073 74,706 (c) (h) (j) 105,779 Income taxes expense / (benefit) — — — — 44,053 (b) 44,053 (Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (6,072 ) — (6,072 ) (21,438 ) 3,719 (23,791 ) Economic Income (Loss) / Net Income (loss) attributable to Cowen Inc. $ (1,580 ) $ 17,415 $ 15,835 $ — $ (76,717 ) $ (60,882 ) Year Ended December 31, 2016 Adjustments Investment Broker-Dealer Total Economic Income/(Loss) Funds Consolidation Other Adjustments US GAAP (dollars in thousands) Revenues Investment banking $ — $ 133,279 $ 133,279 $ — $ — $ 133,279 Brokerage — 207,040 207,040 — (7,860 ) (i) 199,180 Management fees 64,086 3,162 67,248 (1,665 ) (24,971 ) (a) 40,612 Incentive income (loss) 26,274 — 26,274 (714 ) (17,226 ) (a) 8,334 Investment income (loss) 3,015 1,008 4,023 — (4,023 ) (c)(f) — Interest and dividends — — — — 14,732 (c) 14,732 Reimbursement from affiliates — — — (303 ) 10,807 (e) 10,504 Aircraft lease revenue — — — — 4,161 (f) 4,161 Reinsurance premiums — — — — 32,459 (g) 32,459 Other revenue 29,202 565 29,767 — (7,412 ) (g) 22,355 Consolidated Funds revenues — — — 5,949 — 5,949 Total revenues 122,577 345,054 467,631 3,267 667 471,565 Expenses Non interest expense 102,163 369,188 471,351 (429 ) 37,824 (b)(d) 508,746 Interest and dividends 12,827 4,363 17,190 — 12,118 (c) 29,308 Consolidated Funds expenses — — — 9,064 — 9,064 Total expenses 114,990 373,551 488,541 8,635 49,942 547,118 Total other income (loss) — — — 8,532 35,534 (c) 44,066 Income taxes expense / (benefit) — — — — (19,092 ) (b) (19,092 ) (Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (7,821 ) — (7,821 ) (3,164 ) 4,103 (6,882 ) Economic Income (Loss) / Net Income (loss) attributable to Cowen Inc. $ (234 ) $ (28,497 ) $ (28,731 ) $ — $ 9,454 $ (19,277 ) Year Ended December 31, 2015 Adjustments Alternative Investment Broker-Dealer Total Economic Income/(Loss) Funds Consolidation Other Adjustments US GAAP (dollars in thousands) Revenues Investment banking $ — $ 222,781 $ 222,781 $ — $ — $ 222,781 Brokerage — 160,436 160,436 — (2,714 ) 157,722 Management fees 68,989 1,026 70,015 (1,307 ) (26,802 ) (a) 41,906 Incentive income (loss) (1,544 ) — (1,544 ) (736 ) 3,746 (a) 1,466 Investment income (loss) 49,244 13,352 62,596 — (62,596 ) (c) — Interest and dividends — — — — 13,796 (c) 13,796 Reimbursement from affiliates — — — (190 ) 21,747 (e) 21,557 Other revenue 14,492 890 15,382 — (11,656 ) (c) 3,726 Consolidated Funds revenues — — — 1,613 — 1,613 Total revenues 131,181 398,485 529,666 (620 ) (64,479 ) 464,567 Expenses Non interest expense 107,291 362,463 469,754 — 6,090 (b)(c)(d) 475,844 Interest and dividends 11,839 4,745 16,584 — 9,636 (c) 26,220 Consolidated Funds expenses — — — 2,310 — 2,310 Total expenses 119,130 367,208 486,338 2,310 15,726 504,374 Total other income (loss) — — — 8,781 42,505 (c) 51,286 Income taxes expense / (benefit) — — — — (47,496 ) (b) (47,496 ) (Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (8,796 ) — (8,796 ) (5,851 ) (599 ) (15,246 ) Economic Income (Loss) / Net Income (loss) attributable to Cowen Inc. $ 3,255 $ 31,277 $ 34,532 $ — $ 9,197 $ 43,729 The following is a summary of the adjustments made to US GAAP net income (loss) for the segment to arrive at Economic Income (Loss): Funds Consolidation: The impacts of consolidation and the related elimination entries of the Consolidated Funds are not included in Economic Income (Loss). Adjustments to reconcile to US GAAP net income (loss) included elimination of incentive income and management fees earned from the Consolidated Funds and addition of fund expenses excluding management fees paid, fund revenues and investment income (loss). Other Adjustments: (a) Economic Income (Loss) recognizes revenues (i) net of distribution fees paid to agents and (ii) our proportionate share of management and incentive fees of certain real estate operating entities, the healthcare royalty business and the activist business. (b) Economic Income (Loss) excludes income taxes and acquisition related adjustments as management does not consider these items when evaluating the performance of the segment. (c) Economic Income (Loss) recognizes Company income from proprietary trading (including interest and dividends). (d) Economic Income (Loss) recognizes the Company's proportionate share of expenses, for certain real estate operating entities and the activist business, for which the investments are recorded under the equity method of accounting for investments. (e) Reimbursement from affiliates is shown as a reduction of Economic Income expenses, but is included as a part of revenues under US GAAP. (f) Aircraft lease revenue is shown net of expenses in investment income for Economic Income (Loss). (g) Economic Income (Loss) recognizes underwriting income from the Company's insurance related activities, net of expenses, within other revenue. (h) Economic Income (Loss) excludes the bargain purchase gain which resulted from the Convergex Group acquisition. (i) Economic Income (Loss) brokerage revenues included net securities borrowed and securities loaned activities. (j) Economic Income (Loss) excludes gain / (loss) on debt extinguishment.

Regulatory Requirements Regulat

Regulatory Requirements Regulatory (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory [Abstract]
Computation of Net Capital under Securities and Exchange Commission Regulation [Table Text Block]	Subsidiary Net Capital Minimum Net Capital Requirement Excess Net Capital (dollars in millions) Cowen and Company $ 40.2 $ 1.0 $ 39.2 Cowen Execution $ 111.4 $ 2.7 $ 108.7 ATM Execution $ 1.0 $ 0.3 $ 0.7 Cowen Prime $ 12.3 $ 0.3 $ 12.0 Westminster $ 7.6 $ 0.3 $ 7.3 Ramius UK $ 0.2 $ 0.1 $ 0.1 Cowen International Ltd $ 11.5 $ 7.1 $ 4.4 Cowen Execution Ltd $ 3.8 $ 2.6 $ 1.2

Guarantees and Off-Balance Sh60

Guarantees and Off-Balance Sheet Arrangements Details (Tables)	12 Months Ended
	Dec. 31, 2017
Guarantees and Off Balance Sheet Arrangements [Abstract]
Schedule of Subordinated Borrowing [Table Text Block]	The Company maintains uncommitted financing arrangements with large financial institutions, the details of which are summarized below as of December 31, 2017 . Lender Contractual Amount Available Amount Maturity Date Description Pledge Lines (dollars in thousands) BMO Harris Bank $ 150,000 $ 150,000 None Secured DTC Pledge Line Total 150,000 150,000 Revolving Credit Facility BMO Harris Bank 30,000 30,000 August 2, 2018 Unsecured liquidity facility to cover increases in NSCC margin deposit requirements Total Credit Lines $ 180,000 $ 180,000

Supplemental Financial Inform61

Supplemental Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table presents unaudited quarterly results of operations for 2017 and 2016 . These quarterly results reflect all normal recurring adjustments that are, in the opinion of management, necessary for a fair presentation of the results. Revenues and net income (loss) can vary significantly from quarter to quarter due to the nature of the Company's business activities. Cowen Inc. Quarterly Financial Information (Unaudited) Quarter Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 (dollars in thousands, except per share data) Total revenues $ 114,971 $ 160,530 $ 178,830 $ 204,450 Income (loss) before income taxes 14,000 27,800 12,109 (46,947 ) Income tax expense (benefit) 1,911 (785 ) 2,281 40,646 Net income (loss) from continuing operations 12,089 28,585 9,828 (87,593 ) Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds 9,105 21,145 5,162 (11,621 ) Net income (loss) attributable to Cowen Inc. 2,984 7,440 4,666 (75,972 ) Preferred stock dividends 1,698 1,698 1,698 1,698 Net income (loss) attributable to Cowen Inc. common stockholders $ 1,286 $ 5,742 $ 2,968 $ (77,670 ) Earnings (loss) per share: Basic $ 0.05 $ 0.20 $ 0.09 $ (2.51 ) Diluted $ 0.05 $ 0.19 $ 0.09 $ (2.51 ) Weighted average number of common shares: Basic 27,061 28,634 31,271 30,934 Diluted 28,401 29,474 32,246 30,934 Quarter Ended March 31, 2016 June 30, 2016 September 30, 2016 December 31, 2016 (dollars in thousands, except per share data) Total revenues $ 101,039 $ 117,231 $ 131,027 $ 122,268 Income (loss) before income taxes (11,315 ) (39,153 ) 24,018 (5,037 ) Income tax expense (benefit) (3,320 ) (11,992 ) 8,759 (12,539 ) Net income (loss) from continuing operations (7,995 ) (27,161 ) 15,259 7,502 Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds (4,297 ) (16,705 ) 18,478 9,406 Net income (loss) attributable to Cowen Inc. (3,698 ) (10,456 ) (3,219 ) (1,904 ) Preferred stock dividends 1,698 1,698 1,698 1,698 Net income (loss) attributable to Cowen Inc. common stockholders $ (5,396 ) $ (12,154 ) $ (4,917 ) $ (3,602 ) Earnings (loss) per share: Basic (a) $ (0.20 ) $ (0.45 ) $ (0.18 ) $ (0.13 ) Diluted (a) $ (0.20 ) $ (0.45 ) $ (0.18 ) $ (0.13 ) Weighted average number of common shares: Basic (a) 26,591 26,867 26,993 26,973 Diluted (a) 26,591 26,867 26,993 26,973 (a) Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.

Organization and Business (Deta

Organization and Business (Details)	Dec. 05, 2016	Dec. 31, 2017segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.25
Number of business segments		2

Acquisition (Narrative) (Detail

Acquisition (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 01, 2017	Sep. 23, 2016	May 06, 2016
Business Acquisition [Line Items]
Amortization of Intangible Assets	$ 6,100,000	$ 5,000,000	$ 2,700,000
Restructuring Costs	8,763,000	0	0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low	100,000	100,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	15,000,000	15,100,000
Proceeds from divested business, net of cash divested	0	17,303,000	$ 0
Convergex Group [Member]
Business Acquisition [Line Items]
Total estimated purchase price	98,000,000
Payments to Acquire Businesses, Gross	48,600,000
Business Acquisition, Share Price				$ 15.05
Intangible assets, net				$ 10,300,000
Amortization of Intangible Assets	1,400,000
Other Tax Expense (Benefit)	4,700,000
Restructuring Costs	8,800,000
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed	6,000,000
CRT business
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		6,300,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low						$ 0
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed		400,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High						8,000,000
Contractual Obligation						$ 6,000,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	33,200,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	$ 9,300,000
Common Stock Class A | Convergex Group [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	3,162,278
Scenario, Plan [Member] | Convergex Group [Member]
Business Acquisition [Line Items]
Total estimated purchase price	$ 97,962,000
Intangible assets, net				10,270,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net				$ 109,571,000
Goodwill/(Bargain purchase gain)	$ 11,609,000
Alternative Solutions [Member]
Business Acquisition [Line Items]
Assets under Management, Carrying Amount					$ 2,500,000,000
Proceeds from divested business, net of cash divested		$ 17,300,000

Acquisition (Net assets acquire

Acquisition (Net assets acquired) (Details) - Convergex Group [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Jun. 01, 2017
Business Acquisition [Line Items]
Intangible assets		$ 10,300
Total estimated purchase price	$ 98,000
Scenario, Plan [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		30,562
Segregated cash		129,025
Securities owned, at fair value		3,417
Securities borrowed		258,321
Deposits from clearing organizations		52,596
Receivable from brokers		62,983
Receivable from customers		43,469
Fees receivable		36,232
Fixed assets, net		1,325
Intangible assets		10,270
Other assets		7,528
Securities sold, not yet purchased, at fair value		(71)
Securities loaned		(286,359)
Payable to brokers		(74,284)
Payable to customers		(11,801)
Commission management payable		(82,718)
Compensation payable		(31,083)
Notes payable and other debt		(857)
Fees payable		(5,414)
Accounts payable, accrued expenses and other liabilities		(33,570)
Total identifiable net assets acquired and liabilities assumed		$ 109,571
Goodwill/(Bargain purchase gain)	11,609
Total estimated purchase price	$ 97,962

Acquisition (Intangible Assets)

Acquisition (Intangible Assets) (Details) - USD ($) $ in Thousands	Jun. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Total intangible assets		$ 63,036	$ 55,187
Amortization of Intangible Assets		6,100	5,000	$ 2,700
Convergex Group [Member]
Business Acquisition [Line Items]
Trade name	$ 760
Intellectual property	1,790
Customer relationships	7,720
Total intangible assets	$ 10,270
Amortization of Intangible Assets		1,400
Intellectual Property [Member] | Convergex Group [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Trade Names
Business Acquisition [Line Items]
Total intangible assets		10,622	9,962
Customer Relationships [Member]
Business Acquisition [Line Items]
Total intangible assets		$ 41,134	$ 33,874
Customer Relationships [Member] | Convergex Group [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	9 years
Minimum | Convergex Group [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 months 6 days
Minimum | Trade Names
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		7 months 6 days
Minimum | Trade Names | Convergex Group [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 months 6 days
Minimum | Customer Relationships [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Maximum | Convergex Group [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	9 years
Maximum | Trade Names
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		7 years 6 months
Maximum | Trade Names | Convergex Group [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years 7 months 6 days
Maximum | Customer Relationships [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life		14 years

Acquisition (Amortization Expen

Acquisition (Amortization Expense) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
2,018	$ 4,946
2,019	4,168
2,020	3,950
2,021	3,890
2,022	3,108
Thereafter	9,893
Finite-Lived Intangible Assets, Net	29,955
Scenario, Plan [Member] | Convergex Group [Member]
Business Acquisition [Line Items]
2,018	1,258
2,019	1,239
2,020	1,216
2,021	1,216
2,022	1,007
Thereafter	2,931
Finite-Lived Intangible Assets, Net	$ 8,867

Acquisition (Pro Forma) (Detail

Acquisition (Pro Forma) (Details) - Convergex Group [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Revenues	$ 733,744	$ 681,655
Net income (loss)	$ (84,671)	$ (50,516)
Basic (usd per share)	$ (2.75)	$ (1.68)
Diluted (usd per share)	$ (2.75)	$ (1.68)

Significant Accounting Polici68

Significant Accounting Policies - Annual (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)cowenfund	Dec. 31, 2016USD ($)
Organization [Line Items]
Total net assets of consolidated VIEs	$ 482,800	$ 461,600
Deferred rent	$ 12,822	$ 10,335
Minimum
Organization [Line Items]
Redeemable Noncontrolling Interest, Redemption Fee, Percent	1.00%
Maximum
Organization [Line Items]
Redeemable Noncontrolling Interest, Redemption Fee, Percent	5.00%
Telephone and computer equipment | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Telephone and computer equipment | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Computer Software, Intangible Asset | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Computer Software, Intangible Asset | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	8 years
Furniture and Fixtures
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Leasehold improvements | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Leasehold improvements | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Assets Held under Capital Leases
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Aircraft | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Aircraft | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Flight Equipment | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	4 years
Flight Equipment | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Hedge Funds [Member] | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
Real Estate Funds | Minimum
Organization [Line Items]
Asset Management Fees, Percent Fee	0.25%
Real Estate Funds | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	1.50%
Other Healthcare Royalty Partners | Minimum
Organization [Line Items]
Asset Management Fees, Percent Fee	0.20%
Other Healthcare Royalty Partners | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	1.00%
During investment period [Member] | Healthcare Royalty Partners | Minimum
Organization [Line Items]
Asset Management Fees, Percent Fee	1.00%
During investment period [Member] | Healthcare Royalty Partners | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
After investment period [Member] | Healthcare Royalty Partners | Minimum
Organization [Line Items]
Asset Management Fees, Percent Fee	0.50%
After investment period [Member] | Healthcare Royalty Partners | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
Hedge Funds [Member]
Organization [Line Items]
Incentive Fees, Percent Fee	20.00%
Other investment companies
Organization [Line Items]
Number of funds, Consolidated | cowenfund	7

Cash Collateral Pledged (Detail

Cash Collateral Pledged (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cash collateral pledged	$ 17,888	$ 13,342
Facility Leases
Cash collateral pledged	6,100	7,800
Collateral Reinsurance Agreement
Cash collateral pledged	$ 11,800	$ 5,500

Segregated Cash (Details)

Segregated Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Segregated Cash [Abstract]
Segregated Cash	$ 116,268	$ 1,024

Investments of Operating Enti71

Investments of Operating Entities and Consolidated Funds - Securities Owned at Fair Value (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Investment Holdings [Line Items]
Securities owned, at fair value		$ 673,221		$ 700,876
Securities owned, at fair value		165,916		79,237
Common Stock
Investment Holdings [Line Items]
Trading Securities, Equity	[1]	640,065		669,655
Securities owned, at fair value		77,702		28,474
Preferred Stock
Investment Holdings [Line Items]
Trading Securities, Equity	[1]	9,604		15,811
Securities owned, at fair value		50,445		37,343
Warrants and Rights
Investment Holdings [Line Items]
Trading Securities, Equity		9,604	[1]	8,335
Securities owned, at fair value		3,568		3
US Government Securities
Investment Holdings [Line Items]
Trading Securities, Debt	[2]	$ 2,807		$ 3,780
Investment Interest Rate		0.00%		0.00%
Securities owned, at fair value	[3]	$ 34,201		$ 6,994
Corporate Bonds
Investment Holdings [Line Items]
Trading Securities, Debt	[4]	4,909		2,477
Securities owned, at fair value	[5]	$ 0		$ 4,214
Corporate Bonds | Minimum
Investment Holdings [Line Items]
Investment Interest Rate		0.00%		6.25%
Corporate Bonds | Maximum
Investment Holdings [Line Items]
Investment Interest Rate		10.75%		13.00%
Convertible Bonds
Investment Holdings [Line Items]
Trading Securities, Debt	[6]	$ 282		$ 250
Investment Interest Rate				8.00%
Convertible Bonds | Minimum
Investment Holdings [Line Items]
Investment Interest Rate		5.00%
Convertible Bonds | Maximum
Investment Holdings [Line Items]
Investment Interest Rate		12.00%
Trade Claims
Investment Holdings [Line Items]
Trading Securities, Debt		$ 5,950		$ 562
Mutual Fund
Investment Holdings [Line Items]
Trading Securities, Equity	[1]	0		6
Loans
Investment Holdings [Line Items]
Securities owned, at fair value		0		2,209
Warrants and Rights | Estimate of Fair Value Measurement [Member]
Investment Holdings [Line Items]
Trading Securities, Equity	[1]	2,400
Mutual Fund | Estimate of Fair Value Measurement [Member]
Investment Holdings [Line Items]
Trading Securities, Equity	[1]			100
Common Stock | Estimate of Fair Value Measurement [Member]
Investment Holdings [Line Items]
Trading Securities, Equity	[1]	5,200		5,200
Preferred Stock | Estimate of Fair Value Measurement [Member]
Investment Holdings [Line Items]
Trading Securities, Equity	[1]	$ 6,000		$ 7,000
Consolidated Funds | US Government Securities
Investment Holdings [Line Items]
Investment Interest Rate				0.00%
Consolidated Funds | US Government Securities | Minimum
Investment Holdings [Line Items]
Investment Interest Rate		0.00%
Consolidated Funds | US Government Securities | Maximum
Investment Holdings [Line Items]
Investment Interest Rate		5.75%
Consolidated Funds | Corporate Bonds | Minimum
Investment Holdings [Line Items]
Investment Interest Rate				0.00%
Consolidated Funds | Corporate Bonds | Maximum
Investment Holdings [Line Items]
Investment Interest Rate				14.37%
Enterprise Master
Investment Holdings [Line Items]
Securities owned, at fair value		$ 608		$ 2,416
Enterprise Master | Common Stock
Investment Holdings [Line Items]
Securities owned, at fair value		608		835
Enterprise Master | Preferred Stock
Investment Holdings [Line Items]
Securities owned, at fair value		$ 0		$ 1,581
[1]	The Company has elected the fair value option for investments in securities of preferred and common stocks with a fair value of $6.0 million and $5.2 million, respectively, at December 31, 2017 and $7.0 million and $5.2 million, respectively, at December 31, 2016. At December 31, 2017, the Company elected the fair value option for investments in warrants and rights with a fair value of $2.4 million. At December 31, 2016 the Company elected the fair value option for investments in mutual funds with a fair value of $0.1 million
[2]	As of December 31, 2017, maturities ranged from February 2018 to June 2018 with an interest rate of 0%. As of December 31, 2016, maturities ranged from February 2017 to December 2017 with an interest rate of 0%.
[3]	of December 31, 2017, maturities ranged from January 2018 2017 to April 2022 and interest rates ranged from 0% to 5.75%. As of December 31, 2016, the maturity was March 2017 with an interest rate of 0%.
[4]	As of December 31, 2017, maturities ranged from October 2018 to May 2040 and interest rates ranged from 0.00% to 10.75%. As of December 31, 2016, maturities ranged from January 2017 to January 2036 and interest rates ranged from 6.25% to 13.00%.
[5]	As of December 31, 2016, maturities ranged from October 2017 to June 2038 and interest rates ranged from 0% and 14.37%.
[6]	As of December 31, 2017, maturities ranged from February 2018 to March 2018 and interest rates ranged from 5% to 12%. As of December 31, 2016, the maturity was March 2018 with an interest rate of 8%.

Investments of Operating Enti72

Investments of Operating Entities and Consolidated Funds - Derivatives (Details) $ / shares in Units, $ in Thousands		Dec. 05, 2016	Dec. 31, 2017USD ($)contractshares	Dec. 31, 2016USD ($)contract	Dec. 31, 2015USD ($)	Dec. 14, 2017USD ($)	Mar. 10, 2014USD ($)$ / shares
Derivative [Line Items]
Warrants issued					$ 15,200
Cost of hedge transaction and warrant, net							$ 20,500
Stockholders' Equity Note, Stock Split, Conversion Ratio		0.25
Trading days for expiration			80 days
Receivable on derivative contracts, at fair value			$ 69,177	$ 22,901
Payable for derivative contracts, at fair value			42,750	20,762
Receivable on derivatives, Consolidated Funds			2,520	893
Payable for derivative contracts, at fair value, Consolidated Funds			7,130	572
Currency forward
Derivative [Line Items]
Receivable on derivatives, Consolidated Funds			524	18
Payable for derivative contracts, at fair value, Consolidated Funds			11	10
Equity Swap
Derivative [Line Items]
Receivable on derivatives, Consolidated Funds			1,754	731
Payable for derivative contracts, at fair value, Consolidated Funds			7,042	495
Futures
Derivative [Line Items]
Derivative Asset, Notional Amount			3,819	12,421
Receivable on derivative contracts, at fair value			58	104
Derivative Liability, Notional Amount			16,796	38,345
Payable for derivative contracts, at fair value			242	642
Currency Forwards
Derivative [Line Items]
Derivative Asset, Notional Amount			233	80,608
Receivable on derivative contracts, at fair value			5	592
Derivative Liability, Notional Amount			62,439	0
Payable for derivative contracts, at fair value			874	0
Swaps
Derivative [Line Items]
Derivative Asset, Notional Amount			164,664	46,462
Receivable on derivative contracts, at fair value			10,942	468
Derivative Liability, Notional Amount			11,595	9,533
Payable for derivative contracts, at fair value			$ 71	$ 181
Options
Derivative [Line Items]
Derivative Asset, Number of Instruments Held | contract	[1]		283,112	256,097
Receivable on derivative contracts, at fair value	[1]		$ 58,172	$ 21,539
Receivable on derivatives, Consolidated Funds			242	144
Payable for derivative contracts, at fair value, Consolidated Funds			77	67
Foreign Exchange Option
Derivative [Line Items]
Derivative Asset, Notional Amount			0	57,051
Receivable on derivative contracts, at fair value			$ 0	$ 198
Put Option
Derivative [Line Items]
Derivative Liability, Number of Instruments Held | contract	[2]		57,043	23,726
Payable for derivative contracts, at fair value	[2]		$ 41,563	$ 19,939
Receivable on derivatives contracts, at fair value [Member]
Derivative [Line Items]
Receivable on derivative contracts, at fair value			69,177	22,901
Derivative Asset, Fair Value, Gross Asset			69,177	22,901
Derivative Asset, Fair Value, Amount Offset Against Collateral	[3]		0	0
Financial Instruments, Owned and Pledged as Collateral, at Fair Value			0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[4]		10,948	1,382
Derivative asset, net of offset			58,229	21,519
Payable for derivatives contracts, at fair value [Member]
Derivative [Line Items]
Payable for derivative contracts, at fair value			42,750	20,762
Financial Instruments, Owned and Pledged as Collateral, at Fair Value			0	0
Derivative Liability, Fair Value, Gross Liability			42,750	20,762
Derivative Liability, Fair Value, Amount Offset Against Collateral	[3]		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	[4]		1,031	181
Derivative Liability, net of offset			41,719	20,581
Receivables from Brokers-Dealers and Clearing Organizations
Derivative [Line Items]
Collateral posted			$ 13,500	17,100
Common Stock Class A
Derivative [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares			7,012,196
Class of Warrant, Exercise Price of Warrants or Rights | $ / shares							$ 28.72
Other Income [Member]
Derivative [Line Items]
Realized and unrealized gains/(losses) related to derivatives trading activities			$ 3,900	$ (11,200)	$ (5,600)
2022 convertible note [Member] | Convertible Debt
Derivative [Line Items]
Call Option, Fair Value			22,100			$ 23,400
2019 convertible note [Member] | Convertible Debt
Derivative [Line Items]
Call Option, Fair Value			1,500				$ 35,700
Open Option Contracts Written, at Fair Value			$ 300
Class of Warrant, Exercise Price of Warrants or Rights | $ / shares							$ 28.72
[1]	Includes index, equity, commodity future and cash conversion options.
[2]	Includes index, equity, commodity future and cash conversion options.
[3]	Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred.
[4]	Includes the amount of collateral held or posted.

Investments of Operating Enti73

Investments of Operating Entities and Consolidated Funds - Other Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016
Investment Holdings [Line Items]
Other investments	$ 141,548		$ 157,279
Portfolio Funds, Consolidated Funds	374,111		401,465
Portfolio Funds, at fair value
Investment Holdings [Line Items]
Other investments	100,148	[1]	120,023	[2]
Equity Method Investments
Investment Holdings [Line Items]
Other investments	41,099		36,991
Lehman claims, at fair value
Investment Holdings [Line Items]
Other investments	301		265
Enterprise LP [Member]
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	87,221		114,159
Merger Fund [Member]
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	286,890		281,572
Caerus LP [Member]
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	$ 0		$ 5,734
[1]	In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.
[2]	In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.

Investments of Operating Enti74

Investments of Operating Entities and Consolidated Funds - Portfolio Funds - (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Investment Holdings [Line Items]
Other investments		$ 141,548		$ 157,279
Portfolio Funds
Investment Holdings [Line Items]
Other investments		100,148	[1]	120,023	[2]
Portfolio Funds | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[3],[4]	10,133		8,548
Portfolio Funds | RCG Park Liberty GP Member LLC | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[5]	750		598
Portfolio Funds | RCG Longview Debt Fund VI, LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[5]	1,022		0
Portfolio Funds | Starboard Value and Opportunity Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[6]	$ 32,079		$ 27,424
Required notice period, withdrawal		90 days		90 days
Portfolio Funds | Formation 8 Partners Fund I LP
Investment Holdings [Line Items]
Other investments	[7]	$ 28,243		$ 22,234
Portfolio Funds | RCGLongview Debt Fund V, L.P. | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[5]	8,892		16,187
Portfolio Funds | Healthcare Royalty Partners | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[8]	3,452		7,147
Portfolio Funds | Eclipse Ventures Fund I, L.P.
Investment Holdings [Line Items]
Other investments	[9]	3,428		1,790
Portfolio Funds | Lagunita Biosciences, LLC
Investment Holdings [Line Items]
Other investments	[10]	2,400		1,698
Portfolio Funds | RCG LPP2 PNW5 Co-Invest, L.P. | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[11]	3,493		3,152
Portfolio Funds | Starboard Leaders Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[12]	$ 1,276		$ 1,231
Unfunded Commitment cancellation		30 days		30 days
Portfolio Funds | Healthcare Royalty Partners II | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[8]	$ 873		$ 2,091
Portfolio Funds | Quadratic Fund LLC | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[13]	$ 906		$ 6,729
Required notice period, withdrawal		30 days		30 days
Portfolio Funds | RCGL 12E13th LLC | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[5]	$ 237		$ 348
Portfolio Funds | Green Energy Metals Fund, LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[14]	0		6,241
Portfolio Funds | Starboard Partners Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments		$ 0		$ 5,067	[4],[15]
Required notice period, withdrawal		180 days		180 days
Portfolio Funds | Orchard Square Partners Credit Fund LP
Investment Holdings [Line Items]
Other investments		$ 0		$ 4,327	[16]
Portfolio Funds | Orchard Square Partners Credit Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Required notice period, redemption		60 days		60 days
Penalty on redemptions of less than one year		4.00%		4.00%
Portfolio Funds | Other Funds | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[4],[17]	$ 2,964		$ 5,211
Enterprise Master | Portfolio Funds
Investment Holdings [Line Items]
Other investments		99,876		118,027
Multi-strategy [Member] | Enterprise Master | Portfolio Funds | RCG Special Opportunities Fund, Ltd | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[18]	97,345		101,832
Various Strategies [Member] | Enterprise Master | Portfolio Funds | Other Private Investment
Investment Holdings [Line Items]
Other investments		937		8,682
Real Estate Funds | Enterprise Master | Portfolio Funds | RCG Longview Equity Fund, LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[18]	1,266		4,744
Real Estate Funds | Enterprise Master | Portfolio Funds | RCG Longview Debt Fund IV, LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[18]	99		1,637
Real Estate Funds | Enterprise Master | Portfolio Funds | RCG Longview II, LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[18]	229		836
Real Estate Funds | Enterprise Master | Portfolio Funds | Real Estate Funds
Investment Holdings [Line Items]
Other investments	[18]	0		295
Energy Strategy [Member] | Enterprise Master | Portfolio Funds | RCG Renergys, LLC | Affiliated Entity
Investment Holdings [Line Items]
Other investments	[18]	$ 0		$ 1
[1]	In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.
[2]	In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.
[3]	Other private investment represents the Company's closed end investment in a portfolio fund that invests in a wireless broadband communication provider in Italy.
[4]	These portfolio funds are affiliates of the Company.
[5]	RCGL 12E13th LLC, RCG Longview Debt Fund V, L.P., RCG Park Liberty GP Member LLC, and RCG Longview Debt Fund VI, LP are real estate private equity structures and therefore distributions will be made when the underlying investments are liquidated.
[6]	Starboard Value and Opportunity Fund LP permits quarterly withdrawals upon 90 days' notice.
[7]	Formation8 Partners Fund I, L.P. is a private equity fund which invests in early stage and growth transformational information and energy technology companies. Distributions will be made when the underlying investments are liquidated.
[8]	HealthCare Royalty Partners, L.P. and HealthCare Royalty Partners II, L.P. are private equity funds and therefore distributions will be made when cash flows are received from the underlying investments, typically on a quarterly basis.
[9]	Eclipse Ventures Fund I, L.P. is a private equity fund which invests in early stage and growth hardware companies. Distributions will be made when the underlying investments are liquidated.
[10]	Lagunita Biosciences, LLC, a healthcare investment company that creates and grows early stage companies to commercialize impactful translational science that addresses significant clinical needs, is a private equity structure and therefore distributions will be made when the underlying investments are liquidated.
[11]	RCG LPP2 PNW5 Co-Invest, L.P. is a single purpose entity formed to participate in a joint venture which acquired five multi-unit residential rental properties located in the Pacific Northwest. RCG LPP2 PNW5 Co-Invest, L.P. is a private equity structure and therefore distributions will be made when the underlying investments are liquidated.
[12]	Starboard Leaders Fund LP does not permit withdrawals, but instead allows terminations with respect to capital commitments upon 30 days' prior written notice at any time following the first anniversary of an investors' initial capital contribution.
[13]	Quadratic Fund LLC permits redemptions 30 days prior written notice.
[14]	The Green Energy Metals Fund, LP invested the vast majority of its capital in physical off-exchange traded minor metals that are crucial to the production and sustainability of clean energy, emerging technology and energy efficiency. The Company was invested in a managed account specifically targeting cobalt. The Green Energy Metals Fund, LP is a private equity structure and therefore distributions were made when the underlying investments were liquidated
[15]	Starboard Partners Fund LP permitted redemptions on a semi-annual basis on 180 days' prior written notice subsequent to an initial two year lock up.
[16]	Orchard Square Partners Credit Fund LP had a quarterly redemption policy with a 60 day notice period and a 4% penalty on redemptions of investments of less than a year in duration.
[17]	The majority of these funds are affiliates of the Company or are managed by the Company and the investors can redeem from these funds as investments are liquidated.
[18]	Affiliates of the Company.

Investments of Operating Enti75

Investments of Operating Entities and Consolidated Funds - Equity Method Investments - (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Schedule of Equity Method Investments [Line Items]
Expense, equity method investments	$ 7,100	$ 8,500	$ 14,100
Equity method investments	$ 41,099	36,991
Number of investments	3
Net Gains (Losses) on Securities, Derivatives and Other Investments
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments	$ 21,300	14,400	3,400
Surf House Ocean Views Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	14,179	13,522
Starboard Value LP
Schedule of Equity Method Investments [Line Items]
Equity method investments	13,202	12,501
RCG Longview Debt Fund V Partners, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	9,284	7,256
RCG Longview Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	1,149	656
Healthcare Royalty GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	281	583
Healthcare Royalty GP II, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	148	354
RCG Longview Debt Fund IV Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	331	331
Healthcare Royalty GP III, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	764	208
RCG Kennedy House, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	154	183
RCG Longview Equity Management, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	114	114
RCG LPP II GP, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	487	0
RCG Park Liberty GP Member Manager, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	428	141
Equity Method Investee, Other
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 578	1,142
Equity Method Investee, Exceeded Threshold for Income Test [Member]
Schedule of Equity Method Investments [Line Items]
Number of investments	1
Cash	$ 6,046	5,766
Performance & management fee receivable	110,064	48,145
Investments in Portfolio Funds, at fair value	11,251	7,493
Other assets	1,060	1,122
Liabilities	74,256	21,250
Equity	54,165	41,276
Revenues	132,862	87,371	35,268
Expenses	(32,354)	(34,490)	(20,658)
Net realized and unrealized gains (losses)	9,264	9,383	4,259
Net Income	109,772	62,264	18,869
Equity Investment, Two
Schedule of Equity Method Investments [Line Items]
Assets	155,936	88,965
Liabilities	74,316	22,504
Equity	81,620	66,461
Revenues	137,052	90,337	38,571
Expenses	(32,354)	(34,490)	(20,658)
Net realized and unrealized gains (losses)	10,149	(6,305)	9,715
Net Income	$ 114,847	49,542	$ 27,628
Minimum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	57.00%
Clawback Obligation [Member]
Schedule of Equity Method Investments [Line Items]
Contractual obligation		6,200
Clawback Obligation [Member] | RCG Longview Partners II, LLC
Schedule of Equity Method Investments [Line Items]
Contractual obligation	$ 6,200	$ 6,200

Investments of Operating Enti76

Investments of Operating Entities and Consolidated Funds - Securities Sold, Not Yet Purchased (Details) - USD ($)		Dec. 31, 2017		Dec. 31, 2016
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 342,527,000		$ 266,090,000
Securities sold, not yet purchased, at fair value, Consolidated Funds		0	[1]	883,000
Common Stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		342,328,000		263,460,000
Securities sold, not yet purchased, at fair value, Consolidated Funds				211,000
Corporate Bonds
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value	[2]	$ 122,000		2,591,000
Securities sold, not yet purchased, at fair value, Consolidated Funds	[1]			$ 672,000
Corporate Bonds | Minimum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate		3.78%		5.50%
Corporate Bonds | Maximum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate		5.55%		6.25%
Preferred Stock
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value	[2]	$ 77,000		$ 0
Warrants and Rights
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, at fair value		$ 0		$ 39,000
Consolidated Funds | Corporate Bonds | Minimum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate				4.38%
Consolidated Funds | Corporate Bonds | Maximum
Investments Sold, Not yet Purchased [Line Items]
Securities sold, not yet purchased, interest rate				9.25%
[1]	As of December 31, 2016, maturities ranged from September 2019 to September 2023 and interest rates ranged from 4.38% to 9.25%.
[2]	As of December 31, 2017, the maturities ranged from July 2025 to January 2036 with interest rates ranged from 3.78% to 5.55%. As of December 31, 2016, the maturities ranged from April 2021 to January 2036 with interest rates ranged from 5.50% to 6.25%.

Investments of Operating Enti77

Investments of Operating Entities and Consolidated Funds - Securities borrowed and securities loaned (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Securities Borrowed, Gross		$ 443,148,000
Gross amounts offset on the Consolidated Statements of Financial Condition (a)	[1]	0
Gross amounts recognized		443,148,000	$ 0
Securities borrowed, additional amounts, asset		0
Financial instruments		414,778,000
Cash Collateral pledged (b)		0
Net amounts		28,370,000
Securities Loaned, Gross		456,831,000
Gross amounts offset on the Consolidated Statements of Financial Condition (a)	[1]	0
Gross amounts recognized		456,831,000	$ 0
Additional Amounts Available		0
Financial instruments		439,228,000
Cash Collateral pledged (b)		0
Net amounts		$ 17,603,000
[1]	Includes financial instruments subject to enforceable master netting provisions that are permitted to be offset to the extent an event of default has occurred.

Investments of Operating Enti78

Investments of Operating Entities and Consolidated Funds - Securities loaned transactions by remaining contractual maturity and class of collateral pledged (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Stocks	$ 456,831	$ 0
Stocks
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Stocks	456,831
Stocks | Open and Overnight
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Stocks	456,831
Stocks | Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Stocks	0
Stocks | 31 - 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Stocks	0
Stocks | Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Stocks	$ 0

Investments of Operating Enti79

Investments of Operating Entities and Consolidated Funds - Variable Interest Entities (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Total assets of nonconsolidated variable interest entities	$ 5,200	$ 5,300
Total liabilities of nonconsolidated variable interest entities	445.6	997.3
Maximum exposure regarding nonconsolidated variable interest entities	$ 471.3	$ 508.1

Investments of Operating Enti80

Investments of Operating Entities and Consolidated Funds - Indirect Concentration of the Underlying Investments Held by Consolidated Funds (Details) $ in Thousands	Dec. 31, 2017USD ($)investments	Dec. 31, 2016investments
Investment [Line Items]
Concentration of risk, number of investments | investments	1	0
Equity Securities [Member] | Linkem [Member] | ITALY | 517210 Wireless Telecommunications Carriers (except Satellite) [Member] (Deprecated 2016-08-31)
Investment [Line Items]
Percentage of Equity	7.52%
Market Value | $	$ 56,271

Investments of Operating Enti81

Investments of Operating Entities and Consolidated Funds - Merger Master Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Trading Securities	$ 673,221	$ 700,876
Securities sold, not yet purchased, at fair value	342,527	266,090
Common Stock
Investment [Line Items]
Securities sold, not yet purchased, at fair value	342,328	263,460
Common Stock | Merger Master [Member]
Investment [Line Items]
Trading Securities	483,200	835,700
Securities sold, not yet purchased, at fair value	$ 171,200	$ 395,500

Investments of Operating Enti82

Investments of Operating Entities and Consolidated Funds - Merger Master Derivatives (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Asset		$ 69,177	$ 22,901
Derivative Liability		42,750	20,762
Merger Master [Member]
Derivative [Line Items]
Derivative Asset		122,551	4,519
Derivative Liability		2,718	2,408
Put Option
Derivative [Line Items]
Derivative Liability	[1]	41,563	19,939
Put Option | Merger Master [Member]
Derivative [Line Items]
Derivative Liability		1,256	2,285
Options
Derivative [Line Items]
Derivative Asset	[2]	58,172	21,539
Options | Merger Master [Member]
Derivative [Line Items]
Derivative Asset		108,063	4,264
Swaps
Derivative [Line Items]
Derivative Asset		10,942	468
Derivative Liability		71	181
Swaps | Merger Master [Member]
Derivative [Line Items]
Derivative Asset		14,488	255
Derivative Liability		1,249	123
Currency Forwards
Derivative [Line Items]
Derivative Asset		5	592
Derivative Liability		874	0
Currency Forwards | Merger Master [Member]
Derivative [Line Items]
Derivative Liability		$ 213	$ 0
[1]	Includes index, equity, commodity future and cash conversion options.
[2]	Includes index, equity, commodity future and cash conversion options.

Investments of Operating Enti83

Investments of Operating Entities and Consolidated Funds - Caerus Master Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Trading Securities	$ 673,221	$ 700,876
Securities sold, not yet purchased, at fair value	342,527	266,090
Common Stock
Investment [Line Items]
Securities sold, not yet purchased, at fair value	$ 342,328	263,460
Caerus Master [Member] | Common Stock
Investment [Line Items]
Trading Securities		3,200
Securities sold, not yet purchased, at fair value		$ 2,600

Fair Value Measurements for O84

Fair Value Measurements for Operating Entities and Consolidated Funds Assets and Liabilities at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	$ 911,135		$ 804,172
Financial Liabilities Fair Value Disclosure	395,847		294,304
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low	100		100
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	15,000		15,100
Other investments	141,548		157,279
Other Investments, Consolidated Funds	374,111		401,465
Investments	1,426,493		1,362,651
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	$ 802,697		$ 699,940
Percentage of Total Assets at Fair Value	88.10%		87.00%
Percentage of Total Liabilities at Fair Value	91.40%		91.60%
Financial Liabilities Fair Value Disclosure	$ 361,886		$ 269,605
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	$ 28,185		$ 20,868
Percentage of Total Assets at Fair Value	3.10%		2.60%
Percentage of Total Liabilities at Fair Value	2.10%		1.30%
Financial Liabilities Fair Value Disclosure	$ 8,120		$ 3,949
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	$ 80,253		$ 83,364
Percentage of Total Assets at Fair Value	8.80%		10.40%
Percentage of Total Liabilities at Fair Value	6.50%		7.10%
Financial Liabilities Fair Value Disclosure	$ 25,841		$ 20,750
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	342,328		263,460
Common Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	342,328		263,460
Common Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Common Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	122		2,591
Corporate Bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Corporate Bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	122		2,591
Corporate Bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	77
Preferred Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	77
Preferred Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0
Preferred Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0
Warrants and Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		39
Warrants and Rights | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		39
Warrants and Rights | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Warrants and Rights | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Contingent liability payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	3,440	[1]	5,997
Contingent liability payable | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0	[1]	0	[2]
Contingent liability payable | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0	[1]	0	[2]
Contingent liability payable | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	3,440	[1]	5,997	[2]
Futures | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	242		642
Futures | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	242		642
Futures | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Futures | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Currency forward | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	874
Currency forward | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0
Currency forward | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	874
Currency forward | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0
Swaps | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	71		181
Swaps | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Swaps | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	71		181
Swaps | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Put Option | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	41,563		19,939
Put Option | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	19,162		5,186
Put Option | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Put Option | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	22,401		14,753
Trade Claims
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	5,950		562
Trade Claims | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Trade Claims | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Trade Claims | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	5,950		562
US Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	2,807		3,780
US Government Securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	2,807		3,780
US Government Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
US Government Securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	9,604		15,811
Preferred Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	571		0
Preferred Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	918		0
Preferred Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	8,115		15,811
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	640,065		669,655
Common Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	627,011		658,179
Common Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	5,484		1,355
Common Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	7,570		10,121
Convertible Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	282		250
Convertible Bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Convertible Bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Convertible Bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	282		250
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	4,909		2,477
Corporate Bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Corporate Bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	4,909		2,477
Corporate Bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Warrants and Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	9,604		8,335
Warrants and Rights | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	7,087		4,616
Warrants and Rights | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Warrants and Rights | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	2,517		3,719
Mutual Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			6
Mutual Funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			6
Mutual Funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			0
Mutual Funds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			0
Derivative Assets | Futures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	58		104
Derivative Assets | Futures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	58		104
Derivative Assets | Futures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Derivative Assets | Futures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Derivative Assets | Currency forward
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	5		592
Derivative Assets | Currency forward | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Derivative Assets | Currency forward | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	5		592
Derivative Assets | Currency forward | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Derivative Assets | Swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	10,942		468
Derivative Assets | Swaps | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Derivative Assets | Swaps | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	10,942		468
Derivative Assets | Swaps | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Derivative Assets | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	58,172		21,737
Derivative Assets | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	56,717		6,662
Derivative Assets | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		322
Derivative Assets | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,455		14,753
Lehman claims, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	301		265
Other investments	301		265
Lehman claims, at fair value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Lehman claims, at fair value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Lehman claims, at fair value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	301		265
Portfolio Funds, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	100,148	[3]	120,023	[4]
Other Investments, Consolidated Funds	374,111	[3]	401,465	[4]
Equity Method Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	41,099		36,991
Consolidated Funds | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			211
Consolidated Funds | Common Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			211
Consolidated Funds | Common Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			0
Consolidated Funds | Common Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			0
Consolidated Funds | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			672
Consolidated Funds | Corporate Bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			0
Consolidated Funds | Corporate Bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			672
Consolidated Funds | Corporate Bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure			0
Consolidated Funds | Currency forward | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	11		10
Consolidated Funds | Currency forward | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Consolidated Funds | Currency forward | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	11		10
Consolidated Funds | Currency forward | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Consolidated Funds | Equity Swap | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	7,042		495
Consolidated Funds | Equity Swap | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Consolidated Funds | Equity Swap | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	7,042		495
Consolidated Funds | Equity Swap | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Consolidated Funds | Put Option | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	77		67
Consolidated Funds | Put Option | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	77		67
Consolidated Funds | Put Option | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Consolidated Funds | Put Option | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Liabilities Fair Value Disclosure	0		0
Consolidated Funds | US Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	34,201		6,994
Consolidated Funds | US Government Securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	30,552		6,994
Consolidated Funds | US Government Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	3,649		0
Consolidated Funds | US Government Securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	50,445		37,343
Consolidated Funds | Preferred Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Preferred Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		415
Consolidated Funds | Preferred Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	50,445		36,928
Consolidated Funds | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	77,702		28,474
Consolidated Funds | Common Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	77,652		19,467
Consolidated Funds | Common Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		8,712
Consolidated Funds | Common Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	50		295
Consolidated Funds | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			4,214
Consolidated Funds | Corporate Bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			0
Consolidated Funds | Corporate Bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			4,214
Consolidated Funds | Corporate Bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			0
Consolidated Funds | Warrants and Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	3,568		3
Consolidated Funds | Warrants and Rights | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Warrants and Rights | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Warrants and Rights | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	3,568		3
Consolidated Funds | Derivative Assets | Currency forward
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	524		18
Consolidated Funds | Derivative Assets | Currency forward | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Derivative Assets | Currency forward | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	524		18
Consolidated Funds | Derivative Assets | Currency forward | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Derivative Assets | Equity Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,754		731
Consolidated Funds | Derivative Assets | Equity Swap | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Derivative Assets | Equity Swap | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	1,754		731
Consolidated Funds | Derivative Assets | Equity Swap | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		0
Consolidated Funds | Derivative Assets | Options
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	242		144
Consolidated Funds | Derivative Assets | Options | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	242		132
Consolidated Funds | Derivative Assets | Options | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	0		12
Consolidated Funds | Derivative Assets | Options | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring	$ 0		0
Consolidated Funds | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			2,209
Consolidated Funds | Loans | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			0
Consolidated Funds | Loans | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			1,552
Consolidated Funds | Loans | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring			$ 657
[1]	In accordance with the terms of the purchase agreements for acquisitions that closed during the third and fourth quarter of 2015 and the second quarter of 2016, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, December 2020, and June 2018, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2017 can range from $0.1 million to $15.0 million.
[2]	In accordance with the terms of the purchase agreements for acquisitions that closed during 2012 and the third and fourth quarter of 2015, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, and December 2020, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2016 can range from $0.1 million to $15.1 million.
[3]	In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.
[4]	In accordance with US GAAP, certain investments that are measured at fair value using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated statement of financial condition.

Fair Value Measurements for O85

Fair Value Measurements for Operating Entities and Consolidated Funds Unobservable Input Roll Forward (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 15,811,000		$ 12,872,000
Asset, Transfers In		0		0
Asset, Transfers Out		(25,098,000)	[1],[2]	(1,000,000)	[3]
Purchases/(covers)		25,785,000		3,717,000
(Sales)/short buys		(2,956,000)		(218,000)
Realized and unrealized gains (losses), asset		(5,427,000)		440,000
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	486,000		34,000
Balance Asset Value		8,115,000		15,811,000
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		10,121,000		2,278,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		2,670,000		7,099,000
(Sales)/short buys		(2,688,000)		(3,222,000)
Realized and unrealized gains (losses), asset		(2,533,000)		3,966,000
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	(412,000)		3,972,000
Balance Asset Value		7,570,000		10,121,000
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		250,000		819,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		282,000		0
(Sales)/short buys		0		(569,000)
Realized and unrealized gains (losses), asset		(250,000)		0
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	0		0
Balance Asset Value		282,000		250,000
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		14,753,000		18,194,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		(13,298,000)		(3,441,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	(13,298,000)		(3,441,000)
Balance Asset Value		1,455,000		14,753,000
Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,719,000		2,572,000
Asset, Transfers In		2,173,000	[5],[6]	0
Asset, Transfers Out		0		0
Purchases/(covers)		0		1,914,000
(Sales)/short buys		(4,118,000)		(817,000)
Realized and unrealized gains (losses), asset		743,000		50,000
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	510,000		79,000
Balance Asset Value		2,517,000		3,719,000
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		562,000		0
Asset, Transfers In		0		675,000	[7]
Asset, Transfers Out		0		0
Purchases/(covers)		5,865,000		289,000
(Sales)/short buys		(611,000)		(325,000)
Realized and unrealized gains (losses), asset		134,000		(77,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	202,000		(111,000)
Balance Asset Value		5,950,000		562,000
Lehman claims, at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		265,000		299,000
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		36,000		(34,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	36,000		(35,000)
Balance Asset Value		301,000		265,000
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		36,928,000		32,000,000
Asset, Transfers In		22,644,000	[1]	0
Asset, Transfers Out	[2]	(13,668,000)		(11,000,000)
Purchases/(covers)		8,437,000		13,483,000
(Sales)/short buys		(11,903,000)		0
Realized and unrealized gains (losses), asset		8,007,000		2,445,000
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	3,896,000		2,445,000
Balance Asset Value		50,445,000		36,928,000
Consolidated Funds | Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		295,000		0
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		526,000		314,000
(Sales)/short buys		(848,000)		0
Realized and unrealized gains (losses), asset		77,000		(19,000)
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	0		(19,000)
Balance Asset Value		50,000		295,000
Consolidated Funds | Warrants and Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		3,000		0
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		0		0
(Sales)/short buys		0		0
Realized and unrealized gains (losses), asset		3,565,000		3,000
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	3,565,000		3,000
Balance Asset Value		3,568,000		3,000
Consolidated Funds | Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		657,000		0
Asset, Transfers In		0		0
Asset, Transfers Out		0		0
Purchases/(covers)		202,000		590,000
(Sales)/short buys		(1,021,000)		0
Realized and unrealized gains (losses), asset		162,000		67,000
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	0		0
Balance Asset Value		0		657,000
Options, liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		14,753,000		18,194,000
Liability, Transfers In		0		0
Liability, Transfers Out		0		0
Liability, Purchases		0		0
Liability, Sales		0		0
Realized and unrealized gains (losses), liability		7,648,000		(3,441,000)
Change in Unrealized Gain (Loss), instruments still held, liabilities	[4]	7,648,000		(3,441,000)
Balance Liability Value		22,401,000		14,753,000
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		5,997,000		6,158,000
Liability, Transfers In		0		0
Liability, Transfers Out		0		0
Liability, Purchases		0		2,397,000
Liability, Sales		(392,000)		(4,697,000)
Realized and unrealized gains (losses), liability		(2,165,000)		2,139,000
Change in Unrealized Gain (Loss), instruments still held, liabilities	[4]	$ (2,165,000)		0
Balance Liability Value				$ 5,997,000
[1]	The Company transferred investments to a consolidated fund.
[2]	The investments were converted to common stock.
[3]	The entity in which the Company is invested completed an initial public offering.
[4]	Unrealized gains/losses are reported in other income (loss) in the accompanying consolidated statements of operations.
[5]	As part of the preferred stock sale, the sellers received contingent value rights to be paid in the event certain milestones are reached.
[6]	The Company received warrants as part of a transaction.
[7]	The investment undertook a reorganization and subsequently is not traded in an active market.

Fair Value Measurements for O86

Fair Value Measurements for Operating Entities and Consolidated Funds Fair Value Inputs, Unobservable Inputs, Quantitative Information (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 395,847		$ 294,304
Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		3,440	[1]	5,997
Balance Liability Value				5,997		$ 6,158
Trade Claims
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		5,950		562		0
Warrants and Rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		2,517		3,719		2,572
Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		1,455		14,753		$ 18,194
Put Option | Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		41,563		19,939
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		80,253		83,364
Financial Liabilities Fair Value Disclosure		25,841		20,750
Balance Liability Value		$ 25,841		$ 20,750
Level 3 | Options | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		28.00%		40.00%
Level 3 | Options | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility
Level 3 | Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 3,440	[1]	$ 5,997	[2]
Level 3 | Contingent liability payable | Income Approach and Market Approach Valuation Techniques | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		8.00%		8.00%
Level 3 | Contingent liability payable | Income Approach and Market Approach Valuation Techniques | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		23.00%		25.00%
Level 3 | Contingent liability payable | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Assumptions, Weighted Average Volatility Rate		22.00%		23.00%
Level 3 | Contingent liability payable | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 3,440		$ 5,997
Level 3 | Common and Preferred Stock | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				37.00%
Level 3 | Common and Preferred Stock | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Assumptions, Projected cash flow				9.50%
Level 3 | Common and Preferred Stock | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Assumptions, Projected cash flow				10.00%
Level 3 | Common and Preferred Stock | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 5,642		$ 10,917
Level 3 | Common and Preferred Stock | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member] | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Market multiple		4.8		0.8
Level 3 | Common and Preferred Stock | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member] | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Market multiple		8.5		9.3
Level 3 | Trade Claims | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		20.00%		20.00%
Market multiple				6
Level 3 | Trade Claims | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 70		$ 520
Level 3 | Warrants and Rights | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 2,516
Level 3 | Warrants and Rights | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		22.00%
Volatility		61.00%
Fair Value Assumptions, Weighted Average Volatility Rate				73.00%
Level 3 | Warrants and Rights | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				30.00%
Level 3 | Warrants and Rights | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				85.00%
Level 3 | Warrants and Rights | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value				$ 3,719
Level 3 | Other Investments | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[3]	$ 70,570
Level 3 | Other Investments | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[3]			$ 53,455
Level 3 | Options | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		28.00%		40.00%
Level 3 | Options | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility
Level 3 | Options | Derivative Assets | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 1,455
Level 3 | Options | Derivative Assets | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value				$ 14,753
Level 3 | Put Option | Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 22,401		14,753
Level 3 | Put Option | Options | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure				$ 14,753
[1]	In accordance with the terms of the purchase agreements for acquisitions that closed during the third and fourth quarter of 2015 and the second quarter of 2016, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, December 2020, and June 2018, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2017 can range from $0.1 million to $15.0 million.
[2]	In accordance with the terms of the purchase agreements for acquisitions that closed during 2012 and the third and fourth quarter of 2015, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 2018, and December 2020, respectively. The Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2016 can range from $0.1 million to $15.1 million.
[3]	The quantitative disclosures exclude financial instruments for which the determination of fair value is based on prices from recent transactions.

Fair Value Measurements for O87

Fair Value Measurements for Operating Entities and Consolidated Funds Carrying Value Disclosures (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash and cash equivalents		$ 130,052	$ 110,990	$ 157,232	$ 129,509
Cash collateral pledged		17,888	13,342
Segregated Cash		116,268	1,024
Securities Borrowed		443,148	0
Loans Receivable, Net		37,993	31,088
Cash and cash equivalents, Consolidated Funds		21,988	17,761
Securities Loaned		456,831	0
Convertible debt		141,502	130,029
Notes payable and other debt		173,458	77,030
Convertible Debt
Convertible debt, unamortized discount		25,600	17,800
Level 1
Cash and cash equivalents, Fair Value		130,052	110,990
Segregated cash fair value disclosures		116,268	1,024
Cash and cash equivalents, Consolidated Funds, Fair Value		21,988	17,761
Level 2
Cash collateral pledged, Fair Value		17,888	13,342
Securities Borrowed, Fair Value Disclosure		414,763	0
Securities loaned, fair value disclosure		440,162	0
Convertible debt, Fair Value	[1]	172,709	149,545
Notes payable and other debt, Fair Value	[2]	182,352	80,817
Level 3
Loans Receivable, Fair Value Disclosure	[3]	$ 37,993	$ 31,088
[1]	The convertible debt includes the conversion option and is based on the last broker quote available.
[2]	Notes payable and other debt are based on the last broker quote available.
[3]	The fair market value of level 3 loans is calculated using discounted cash flows.

Deposits with Clearing Organi88

Deposits with Clearing Organizations, Brokers and Banks (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposits with Clearing Organizations, Brokers and Banks [Abstract]
Deposits with clearing organizations, brokers and banks	$ 93,996	$ 8,939

Receivables from and payables89

Receivables from and payables to brokers, dealers and clearing organizations (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Brokers and Dealers [Abstract]
Receivable from Broker-dealers	$ 409,499	$ 78,898
Securities Failed-to-Deliver	87,820	0
Receivable from Clearing organizations	6,126	0
Stock borrow interest receivable	4,733	0
Receivable from brokers, dealers and clearing organizations	508,178	78,898
Payable to Broker-Dealers	145,860	210,309
Securities Failed-to-Receive	53,540	0
Payable to clearing organizations	48,257	0
Stock loan interest payable	4,496	0
Payable to brokers, dealers and clearing organizations	$ 252,153	$ 210,309

Receivable from and Payable t90

Receivable from and Payable to Customers (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Receivables and Payable to Customers [Abstract]
Receivables from Customers, net of allowance of $1,550 and $0, respectively	$ 49,891	$ 0
Payables to Customers	$ 352,467	$ 0

Fixed Assets (Details)

Fixed Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 68,851	$ 66,275
Less: Accumulated depreciation and amortization		(28,355)	(23,867)
Fixed assets, net		40,496	42,408
Other Depreciation and Amortization		7,000	7,700	$ 6,800
Gain (Loss) on Disposition of Property Plant Equipment		2,346	0	(54)
Telephone and computer equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		3,465	2,787
Computer software
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		2,914	2,167
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		1,423	1,204
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		36,702	35,092
Assets acquired under capital leases-equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		6,920	4,075
Depreciation		1,000	1,200	$ 1,500
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation		3,400	2,400
Aircraft and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		17,369	20,893
Less: Accumulated depreciation and amortization		(1,800)	(1,700)
Gain (Loss) on Disposition of Property Plant Equipment	$ 2,300
Depreciation		1,500	1,700
Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 58	$ 57

Goodwill and Intangibles Schedu

Goodwill and Intangibles Schedule of Goodwill by Segment (Details) (Annual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, Gross	$ 80,363	$ 80,363	$ 78,046
Goodwill	60,678	58,361
Goodwill, Acquired During Period	0	3,519
Goodwill, Other Changes	0	(1,202)
Goodwill impairment	0	0
Goodwill, Impaired, Accumulated Impairment Loss	19,685	19,685	19,685
Goodwill	60,678	60,678
Investment Management
Goodwill [Roll Forward]
Goodwill, Gross	29,026	29,026	30,228
Goodwill	18,826	20,028
Goodwill, Acquired During Period	0	0
Goodwill, Other Changes	0	(1,202)
Goodwill impairment	0	0
Goodwill, Impaired, Accumulated Impairment Loss	10,200	10,200	10,200
Goodwill	18,826	18,826
Broker-Dealer
Goodwill [Roll Forward]
Goodwill, Gross	51,337	51,337	47,818
Goodwill	41,852	38,333
Goodwill, Acquired During Period	0	3,519
Goodwill, Other Changes	0	0
Goodwill impairment	0	0
Goodwill, Impaired, Accumulated Impairment Loss	9,485	9,485	$ 9,485
Goodwill	$ 41,852	41,852
CRT business | Broker-Dealer
Goodwill [Roll Forward]
Goodwill, Acquired During Period		3,500
Finite-lived Intangible Assets Acquired		$ 5,100
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		8 years 1 month 6 days
Alternative Solutions [Member] | Investment Management
Goodwill [Roll Forward]
Goodwill, Other Changes		$ 1,200

Goodwill and Intangibles Sche93

Goodwill and Intangibles Schedule of Intangible Assets (Details) (Annual) - USD ($) $ in Thousands	Jun. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 63,036	$ 55,187
Intangible assets, accumulated amortization (in dollars)		(33,081)	(29,418)
Intangible Assets, Net		29,955	25,769
Amortization of Intangible Assets		6,100	5,000	$ 2,700
Impairment of Intangible Assets, Finite-lived		$ 0	0
Investment Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 10,622	9,962
Intangible assets, accumulated amortization (in dollars)		(10,555)	(9,689)
Intangible Assets, Net		67	273
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		41,134	33,874
Intangible assets, accumulated amortization (in dollars)		(15,733)	(12,948)
Intangible Assets, Net		25,401	20,926
Customer Contracts [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 800	800
Finite-Lived Intangible Asset, Useful Life		1 year 2 months 12 days
Intangible assets, accumulated amortization (in dollars)		$ (800)	(800)
Intangible Assets, Net		0	0
Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		2,237	2,268
Intangible assets, accumulated amortization (in dollars)		(1,479)	(818)
Intangible Assets, Net		758	1,450
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		8,243	8,283
Intangible assets, accumulated amortization (in dollars)		(4,514)	(5,163)
Intangible Assets, Net		3,729	3,120
Cowen Equity Finance [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of Intangible Assets, Finite-lived				$ 0
Convergex Group [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 10,270
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years 8 months 12 days
Intangible assets, net	$ 10,300
Amortization of Intangible Assets		$ 1,400
Convergex Group [Member] | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	9 years
Minimum | Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		7 months 6 days
Minimum | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Minimum | Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Minimum | Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Minimum | Convergex Group [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 months 6 days
Minimum | Convergex Group [Member] | Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 months 6 days
Maximum | Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		7 years 6 months
Maximum | Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		14 years
Maximum | Noncompete Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years
Maximum | Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		10 years
Maximum | Convergex Group [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	9 years
Maximum | Convergex Group [Member] | Trade Names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years 7 months 6 days
Broker-Dealer | CRT business
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired			$ 5,100
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			8 years 1 month 6 days
Broker-Dealer | Minimum | CRT business
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			1 year
Broker-Dealer | Maximum | CRT business
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			9 years

Goodwill and Intangibles Amorti

Goodwill and Intangibles Amortization of Intangible Assets (Details) (Annual) $ in Thousands	Dec. 31, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 4,946
2,019	4,168
2,020	3,950
2,021	3,890
2,022	3,108
Thereafter	9,893
Finite-Lived Intangible Assets, Net	$ 29,955

Goodwill and Intangibles Qtlry

Goodwill and Intangibles Qtlry (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill, Acquired During Period	$ 0	$ 3,519
Amortization of Intangible Assets	6,100	5,000	$ 2,700
Goodwill, Other Changes	0	(1,202)
Goodwill Impairment	$ 0	$ 0

Other Assets (Details)

Other Assets (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense		$ 13,267	$ 10,669
Deposits		877	5,322
Reinsurance Receivables, net	[1]	14,014	5,187
Loan Receivable		0	3,700	[2]
Tax receivables		1,457	3,267
Miscellaneous Receivables		19,565	0
Interest and dividends receivable		1,021	718
Deferred acquisition costs	[1]	1,978	677
Deferred rent asset		0	52
Short term bridge loan	[3]	19,851	4,476
Other Assets, Miscellaneous		16,238	4,338
Other Assets		$ 88,268	$ 38,406
Loans
Effective interest rate			12.00%
Loans | Hollenfels [Member] | Minimum
Effective interest rate		8.00%	8.00%
Loans | Hollenfels [Member] | Maximum
Effective interest rate		8.50%	8.50%
[1]	Balances relate to the Company's reinsurance business entered into during 2016 (See Note 17).
[2]	As of December 31, 2016, the maturity was August 2017 with interest rate of 12%.
[3]	As of December 31, 2017, the maturity is January 2024, with interest rate of 8% for the first five years and 8.5% for the remainder of the term, related to the Company's commercial reinsurance activities. As of December 31, 2016, the maturity is January 2024, with interest rate of 8% for the first five years and 8.5% for the remainder of the term, related to the Company's commercial reinsurance activities.

Accounts Payable Accrued Expe97

Accounts Payable Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016
Accounts Payable [Line Items]
Deferred rent obligations		$ 12,822		$ 10,335
Contingent consideration payable		3,440		5,997
Equity in RCG Longview partners II, LLC		6,022		5,948
Interest and Dividends Payable		2,891		3,541
Loss reserves and claims incurred but not reported	[1]	9,464		3,455
Professional fees payable		5,008		3,143
Unearned Premiums	[1]	6,116		2,375
Fees payable		798		1,093
Accrued tax liabilities		7,482		456
Litigation reserve		3,000		0
Accrued expenses and accounts payable		39,490	[2]	11,182
Accounts payable, accrued expenses and other liabilities		96,533		$ 47,525
Hollenfels [Member]
Accounts Payable [Line Items]
Accrued Liabilities		$ 18,000
[1]	Balances relate to the Company's reinsurance business entered into during 2016 (See Note 17).
[2]	As of December 31, 2017, the balance includes premiums accrued but not yet paid of $18.0 million related to the Company’s reinsurance business.

Commission Management Payable (

Commission Management Payable (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commission Management Payable [Abstract]
Commission management payable	$ 70,451	$ 3,590

Redeemable Non-Controlling In99

Redeemable Non-Controlling Interests in Consolidated Subsidiaries and Funds (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 440,604				$ 379,205				$ 440,604	$ 379,205
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	(11,621)	$ 5,162	$ 21,145	$ 9,105	9,406	$ 18,478	$ (16,705)	$ (4,297)	23,791	6,882	$ 15,246
Operating Entities
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	6,113				7,638				6,113	7,638
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									2,353	3,717	9,503
Consolidated Funds
Noncontrolling Interest [Line Items]
Redeemable non-controlling interests in consolidated subsidiaries and funds	$ 434,491				$ 371,567				434,491	371,567
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									$ 21,438	$ 3,165	$ 5,743

Reinsurance (Details)

Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Historical Average Claims Ratios, Period, Minimum		5 years
Historical Average Claims Ratios, Period, Maximum		10 years
Hollenfels [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Share of incurred and paid claims	$ 15.3
Share of claims incurred but not reported		$ 5.8

Share-Based Compensation and101

Share-Based Compensation and Employee Ownership Plans Narrative (Details) $ in Millions	Dec. 05, 2016	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.25
Equity Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance under compensation plan, in shares | shares		0
Stock-compensation expense recognized in connection with compensation plan		$ 28.4	$ 26	$ 21.7
Tax benefit of stock-compensation expense recognized in connection with compensation plan		$ 7.7	$ 11.4	$ 5
Equity Plans | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, initial term		7 years
Equity Plans | Employee Stock Option | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period		2 years
Equity Plans | Employee Stock Option | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period		5 years
Equity Plans | Restricted Shares and Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense		$ 56.4
Vested, shares | shares		2,036,366	1,487,092
Equity Plans | Restricted Stock | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period		2 years
Equity Plans | Restricted Stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period		5 years
Equity Plans | Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
SAR's, initial term		5 years
Unrecognized compensation expense			$ 0.1
Vested, shares | shares		25,000	0
Deferred Cash Award | Cowen Group, Inc. 2010 Equity and Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred cash awards granted		$ 24.1
Stock compensation award, vesting period		4 years
Convergex Group [Member] | Deferred Cash Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred cash awards granted		$ 2.4

Share-Based Compensation and102

Share-Based Compensation and Employee Ownership Plans Deferred Cash (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Cowen Group, Inc. 2010 Equity and Incentive Plan | Deferred Cash Award
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred cash awards granted	$ 24.1
Deferred cash awards, vesting period	4 years
Deferred cash award, interest rate	0.70%
Deferred cash awards, unrecognized compensation expense	$ 35
Convergex Group [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Arrangement with Individual, Requisite Service Period	27 months
Convergex Group [Member] | Deferred Cash Award
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred cash awards granted	$ 2.4

Share-Based Compensation and103

Share-Based Compensation and Employee Ownership Plans Stock Options (Details) $ / shares in Units, $ in Thousands		Dec. 05, 2016	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio		0.25
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate			0.00%
Weighted Average Exercise Price/Share
Weighted average remaining term, options outstanding					1 year 7 months 6 days
Weighted average remaining term, options exercisable				1 month 6 days
Aggregate Intrinsic Value
Closing stock price, in dollars per share			$ 13.65	$ 15.50
Equity Plans
Shares Subject to Option
Balance outstanding, beginning of period, shares | shares			4,167	4,167
Options granted, shares | shares			0	0
Stock Options exercised, shares | shares			0	0
Options expired, shares | shares			(4,167)	0
Balance outstanding, end of period, shares | shares			0	4,167	4,167
Options exercisable, shares | shares			0	4,167
Weighted Average Exercise Price/Share
Balance outstanding, beginning of period, in dollars per share			$ 19.56	$ 19.56
Options granted, in dollars per share			0	0
Options exercised, in dollars per share			0	0
Options expired, in dollars per share			19.56	0
Balance outstanding, end of period, in dollars per share			0	19.56	$ 19.56
Options exercisable, in dollars per share			$ 0	$ 19.56
Weighted average remaining term, options outstanding			0 years	1 month 6 days
Weighted average remaining term, options exercisable			0 years
Aggregate Intrinsic Value
Balance outstanding, beginning of period | $	[1]		$ 0	$ 87
Balance outstanding, end of period | $	[1]		0	0	$ 87
Options exercisable | $	[1]		$ 0	$ 0
[1]	Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016.

Share-Based Compensation and104

Share-Based Compensation and Employee Ownership Plans SARs (Details) $ / shares in Units, $ in Thousands		Dec. 05, 2016	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio		0.25
Aggregate Intrinsic Value
Closing stock price, in dollars per share			$ 13.65	$ 15.50
Stock Appreciation Rights
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Exercisable, Weighted remaining contractual term			0 years
Equity Plans
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $	[1]		$ 0	$ 0
Equity Plans | Stock Appreciation Rights
Shares Subject to Option
Balance outstanding, beginning of period, shares | shares			100,000	100,000
Granted, shares | shares			0	0
Acquired, shares | shares			(25,000)	0
Expired, shares | shares			0	0
Balance outstanding, end of period, shares | shares			75,000	100,000	100,000
Balance exercisable, shares | shares			0
Weighted Average Exercise Price/Share
Balance outstanding, beginning of period, in dollars per share			$ 11.60	$ 11.60
Granted, in dollars per share			0	0
Acquired, in dollars per share			11.60	0
Expired, in dollars per share			0	0
Balance outstanding, end of period, in dollars per share			$ 11.60	$ 11.60	$ 11.60
Weighted Average Remaining Term Outstanding			2 months 16 days	1 year 2 months 16 days	2 years 2 months 16 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding | $	[2]		$ 173	$ 435
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $	[2]				$ 558
Unrecognized compensation expense | $				$ 100
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Exercisable, Weighted Average Grant Date Fair Value			$ 0
[1]	Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016.
[2]	Based on the Company's closing stock price of $13.65 on December 31, 2017 and $15.50 on December 31, 2016.

Share-Based Compensation and105

Share-Based Compensation and Employee Ownership Plans Restricted Shares and Restricted Stock Units (Details) $ / shares in Units, $ in Millions	Dec. 05, 2016	Mar. 31, 2016shares	Jan. 31, 2014shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.25
Equity Plans | Restricted Shares and Restricted Stock Units (RSUs)
Nonvested Restricted Shares and Restricted Stock Units
Balance outstanding, beginning of period, shares				5,717,932	5,370,091
Granted, shares				2,255,441	2,157,403
Vested, shares				(2,036,366)	(1,487,092)
Canceled, shares				0	0
Forfeited, shares				(357,714)	(322,470)
Balance outstanding, end of period, shares				5,579,293	5,717,932
Weighted-Average Grant Date Fair Value
Balance outstanding, beginning of period, in dollars per share | $ / shares				$ 16.23	$ 16.68
Granted, in dollars per share | $ / shares				14.98	14.02
Vested, in dollars per share | $ / shares				14.64	14.95
Canceled, in dollars per share | $ / shares				0	0
Forfeited, in dollars per share | $ / shares				15.77	14.89
Balance outstanding, end of period, in dollars per share | $ / shares				$ 16.33	$ 16.23
Unrecognized compensation expense | $				$ 56.4
Weighted-average recognition period for unrecognized compensation expense				2 years 3 months 8 days
Equity Plans | Performance based restricted stock
Nonvested Restricted Shares and Restricted Stock Units
Granted, shares		700,000	481,438
Forfeited, shares				(109,375)
Non-employee Director | Equity Plans | Restricted Stock Units (RSUs)
Nonvested Restricted Shares and Restricted Stock Units
Balance outstanding, beginning of period, shares				162,176
Balance outstanding, end of period, shares				191,962	162,176
Weighted-Average Grant Date Fair Value
Granted, shares				56,519	56,100
Maximum
Nonvested Restricted Shares and Restricted Stock Units
Percent of RSU's earned				150.00%
Minimum
Nonvested Restricted Shares and Restricted Stock Units
Percent of RSU's earned				0.00%

Defined Contribution Plans (Det

Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plans [Abstract]
Defined Contribution Plan, Cost	$ 0.7	$ 0.5	$ 0.5

Income Taxes Income Tax Expense

Income Taxes Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Deferred tax asset, deduction limitation	$ 2,400								$ 2,400
Operating Loss Carryforwards	1,800								1,800
Current tax expense/(benefit)
Federal									421	$ 1,268	$ (635)
State and local									2,034	1,972	313
Foreign									428	262	348
Total									2,883	3,502	26
Deferred tax expense/(benefit)
Federal									44,071	(22,834)	(37,979)
Foreign									(2,938)	(1,900)	(7,420)
Foreign									37	2,140	(2,123)
Total									(41,170)	22,594	47,522
Total Tax expense/(benefit)	40,646	$ 2,281	$ (785)	$ 1,911	$ (12,539)	$ 8,759	$ (11,992)	$ (3,320)	44,053	(19,092)	(47,496)
Income (Loss) from Continuing Operations before Income Taxes, Domestic									3,900	(29,500)	8,000
Income (Loss) from Continuing Operations before Income Taxes, Foreign									3,100	(2,000)	3,500
Unrecognized Tax Benefits	3,947				$ 0				3,947	$ 0	$ 0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1,100								1,100
Unrecognized Tax Benefits, Interest on Income Taxes Expense									300
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ 1,500								1,500
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense (Benefit)									$ 46,600

Income Taxes Income Tax Rate Re

Income Taxes Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Pre-tax loss at U.S. statutory rate	35.00%	35.00%	35.00%
Dividend received deduction	(25.90%)	(0.00%)	(0.00%)
Bargain purchase gain	(34.80%)	0.00%	0.00%
Basis adjustment on investments	65.20%	0.00%	0.00%
Nondeductible expenses	14.20%	0.00%	0.00%
Deferred asset recognition	0.00%	0.00%	(323.80%)
Unrecognized gains on foreign subsidiaries	0.00%	38.70%	0.00%
Change in valuation allowance	0.00%	(6.70%)	0.00%
Impact of tax law change	669.80%	0.00%	(27.90%)
State and foreign tax	25.30%	1.30%	(39.60%)
Reversal of income attributable to redeemable non-controlling interests	(119.60%)	1.30%	(46.50%)
Other, net	3.70%	(9.00%)	(11.00%)
Total	632.90%	60.60%	(413.80%)

Income Taxes Deferred Tax Asset

Income Taxes Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets, net of valuation allowance
Net operating loss	$ 78,650	$ 126,037
Deferred compensation	39,992	44,966
Goodwill	1,042	4,758
Deferred Tax Assets, Investments	5,776	0
Fixed assets	0	3,541
Tax credits	4,419	2,898
Acquired lease liability	3,473	4,111
Other	2,696	2,238
Valuation allowance	136,048	188,549
Valuation allowance	2,103	2,119
Deferred tax assets, net of valuation allowance	133,945	186,430
Deferred tax liabilities
Unrealized gains on investments	(7,523)	(20,774)
Amortization of bond discount	6,402	0
Other	3,697	0
Total deferred tax liabilities	17,622	20,774
Deferred tax assets/(liabilities), net	$ 116,323	$ 165,656

Income Taxes Summary of Operati

Income Taxes Summary of Operating Loss Carryforwards (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Income Taxes Receivable	$ 0
Accrued Income Taxes	6,300,000
Valuation allowance	2,103,000	$ 2,119,000
Deferred Tax Assets, Gross	136,048,000	188,549,000
Deferred Tax Liabilities, Gross	17,622,000	20,774,000
Deferred Income Tax Expense (Benefit)	41,170,000	(22,594,000)	$ (47,522,000)
Operating Loss Carryforwards	1,800,000
Other	2,696,000	$ 2,238,000
Deferred tax asset, deduction limitation	2,400,000
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 248,400,000
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036
New York State Division of Taxation and Finance [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 93,400,000
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 130,800,000
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036
Inland Revenue, Hong Kong [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 12,800,000
Luxembourg Reinsurance Companies
Operating Loss Carryforwards [Line Items]
Valuation allowance	146,000,000
Other	146,000,000
Deferred Tax Liabilities, Gross, Current	349,100,000
LaBranche and Co Inc. [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	50,100,000
Deferred tax asset, deduction limitation	$ 6,700,000

Income Taxes Unrecognized Tax B

Income Taxes Unrecognized Tax Benefits - Annual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 3,947	$ 0	$ 0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1,100
Unrecognized Tax Benefits, Interest on Income Taxes Expense	300
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	1,500
Unrecognized Tax Benefits, Increase Resulting from Acquisition	2,847	0
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	$ 1,100	$ 0

Income Taxes - Tax Cuts and Jo

Income Taxes - Tax Cuts and Jobs Act (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Income Tax Disclosure [Abstract]
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense (Benefit)	$ 46.6

Commitments and Contingencie113

Commitments and Contingencies (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease Obligations
Net rent expense		$ 22,600,000	$ 20,300,000	$ 18,500,000
Future minimum annual lease and service payments
Sublease income related to operating leases		1,100,000	2,200,000	$ 2,300,000
Clawback Obligation
Future minimum annual lease and service payments
Contractual obligation			6,200,000
RCG Longview Partners II, LLC | Clawback Obligation
Future minimum annual lease and service payments
Contractual obligation		6,200,000	$ 6,200,000
Equipment Leases
Future minimum annual lease and service payments
Contractual Obligation, Due in next fiscal year	[1]	3,511,000
Contractual Obligation, Due in Second Year	[1]	1,599,000
Contractual Obligation, Due in Third Year	[1]	669,000
Contractual Obligation, Due in Fourth Year	[1]	639,000
Contractual Obligation, Due in Fifth Year	[1]	420,000
Thereafter	[1]	0
Future minimum annual lease and service payments	[1]	6,838,000
Service Payments
Future minimum annual lease and service payments
Contractual Obligation, Due in next fiscal year		21,631,000
Contractual Obligation, Due in Second Year		10,987,000
Contractual Obligation, Due in Third Year		1,539,000
Contractual Obligation, Due in Fourth Year		337,000
Contractual Obligation, Due in Fifth Year		0
Thereafter		0
Future minimum annual lease and service payments		34,494,000
Facility Leases
Future minimum annual lease and service payments
Contractual Obligation, Due in next fiscal year	[2]	25,960,000
Contractual Obligation, Due in Second Year	[2]	21,453,000
Contractual Obligation, Due in Third Year	[2]	17,626,000
Contractual Obligation, Due in Fourth Year	[2]	17,592,000
Contractual Obligation, Due in Fifth Year	[2]	11,942,000
Thereafter	[2]	7,354,000
Future minimum annual lease and service payments	[2]	$ 101,927,000
[1]	Equipment Leases include the Company's commitments relating to operating and capital leases. See Note 23 for further information on the capital lease minimum payments which are included in the table.
[2]	The Company has entered into various agreements to sublease certain of its premises. The Company recorded sublease income related to these leases of $1.1 million, $2.2 million, and $2.3 million and for the years ended December 31, 2017, 2016, and 2015 respectively.

Commitments and Contingencies S

Commitments and Contingencies Schedules of Unfunded Commitments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)cowenfund
Unfunded Commitments
Other Commitments [Line Items]
Number of Real Estate Investments | cowenfund	6
Real Estate Funds
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 19.5	[1]
Real Estate Funds | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	4 years
Healthcare Royalty Partners
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 6.2	[2]
Healthcare Royalty Partners | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	2 years
Formation 8 Partners Hardware Fund I, L.P. [Member]
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 0.4
Formation 8 Partners Hardware Fund I, L.P. [Member] | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	7 years
Lagunita Biosciences, LLC
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 2
Lagunita Biosciences, LLC | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	3 years
Eclipse Fund II, L.P. [Member]
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 0.9
Eclipse Fund II, L.P. [Member] | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	8 years
Eclipse Continuity Fund I, L.P. [Member]
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 0.6
Eclipse Continuity Fund I, L.P. [Member] | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	9 years
[1]	The Company had unfunded commitments pertaining to capital commitments in six real estate investments held by the Company, all of which pertain to related party investments. Such commitments can be called at any time up to four years, subject to advance notice.
[2]	The Company is a limited partner of the HealthCare Royalty Partners funds (which are managed by Healthcare Royalty Management) and is a member of HealthCare Royalty Partners General Partners. The Company will make its pro-rata investment in the HealthCare Royalty Partners funds along with the other limited partners.

Convertible Debt and Notes P115

Convertible Debt and Notes Payable (Details)		Dec. 05, 2016	Dec. 31, 2017USD ($)letters_of_credit	Dec. 31, 2017USD ($)letters_of_credit	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Jan. 31, 2014USD ($)	Dec. 14, 2017USD ($)$ / shares	Dec. 08, 2017USD ($)	Jan. 31, 2016	Mar. 10, 2014USD ($)$ / shares
Debt and Capital Lease Obligations [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio		0.25
Components of short-term borrowings and other debt
Convertible debt			$ 141,502,000	$ 141,502,000	$ 130,029,000
Note payable			132,970,000	132,970,000	60,953,000
Loans Payable to Bank			28,121,000	28,121,000	0
Other Notes Payable			8,247,000	8,247,000	14,237,000
Capital lease obligations			4,120,000	4,120,000	1,840,000
Debt, Long-term and Short-term, Combined Amount			314,960,000	314,960,000	207,059,000
Amortization of debt discount				7,435,000	6,885,000	$ 6,302,000
Cash convertible note hedge transaction				135,000,000	0	0
Purchase of treasury stock, cost				19,500,000			$ 300,000
Letter of credit, borrowing capacity			180,000,000	180,000,000
Capital Lease Obligations Incurred								$ 6,900,000
Capital Leases, Income Statement, Interest Expense				100,000	100,000	200,000
Future minimum lease payments for capital lease obligations
2,017			2,059,000	2,059,000
2,018			717,000	717,000
2,019			639,000	639,000
2,020			639,000	639,000
2,021			420,000	420,000
Thereafter			0	0
Subtotal			4,474,000	4,474,000
Less: Amount representing interest	[1]		(354,000)	(354,000)
Capital lease obligations			$ 4,120,000	$ 4,120,000	1,840,000
Number of Letters of Credit | letters_of_credit			8	8
Minimum
Components of short-term borrowings and other debt
Capital Lease Obligation, Initial Term				48 months
Capital leases, interest rate			3.70%	3.70%
Maximum
Components of short-term borrowings and other debt
Capital Lease Obligation, Initial Term				60 months
Capital leases, interest rate			5.69%	5.69%
Letter of Credit, San Francisco Office, Expires January 2019 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			$ 710,157	$ 710,157
Letter of Credit, Connecticut Office, Expires January 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			65,000	65,000
Letter of Credit, Boston Office, Expires March 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			381,700	381,700
Letter of Credit, NY Office 1, Expires April 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			354,939	354,939
Letter of Credit, NY Office 2, Expires May 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			69,750	69,750
Letter of Credit, NY Office 3, Expires October 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			595,540	595,540
Letter of Credit, NY Office 4, Expires October 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			2,249,523	2,249,523
Letter of Credit, NY Office 5, Expires November 2018 | Letter of Credit
Components of short-term borrowings and other debt
Letter of credit, borrowing capacity			1,600,000	1,600,000
Convertible Debt
Components of short-term borrowings and other debt
Convertible debt, unamortized discount			25,600,000	25,600,000	17,800,000
Repayments on long-term and short-term borrowings
2,017			4,840,000	4,840,000
2,018			38,925,000	38,925,000
2,019			4,050,000	4,050,000
2,020			4,050,000	4,050,000
2,021			139,050,000	139,050,000
Thereafter			0	0
Subtotal			190,915,000	190,915,000
Less: Amount representing interest	[1]		(49,413,000)	(49,413,000)
Senior Notes
Components of short-term borrowings and other debt
Note payable			132,970,000	132,970,000
Repayments on long-term and short-term borrowings
2,017			10,340,000	10,340,000
2,018			10,143,000	10,143,000
2,019			10,143,000	10,143,000
2,020			10,143,000	10,143,000
2,021			10,143,000	10,143,000
Thereafter			188,715,000	188,715,000
Subtotal			239,627,000	239,627,000
Less: Amount representing interest	[1]		$ (106,657,000)	$ (106,657,000)
Notes Payable to Banks [Member]
Components of short-term borrowings and other debt
Short-term Debt, Percentage Bearing Variable Interest Rate			3.75%	3.75%
Debt Instrument, Face Amount			$ 28,200,000	$ 28,200,000
Interest Expense, Debt				700,000
Insurance Note [Member]
Components of short-term borrowings and other debt
Interest rate											1.50%
Debt Instrument, Periodic Payment, Principal				200,000
Short-term Debt, Maximum Amount Outstanding During Period				2,100,000
Loans
Repayments on long-term and short-term borrowings
2,017			0	0
2,018			28,901,000	28,901,000
2,019			0	0
2,020			0	0
2,021			0	0
Thereafter			0	0
Subtotal			28,901,000	28,901,000
Less: Amount representing interest	[1]		(780,000)	(780,000)
Insurance Note and Aircraft [Member]
Repayments on long-term and short-term borrowings
2,017			2,032,000	2,032,000
2,018			3,410,000	3,410,000
2,019			1,363,000	1,363,000
2,020			2,512,000	2,512,000
2,021			0	0
Thereafter			0	0
Subtotal			9,317,000	9,317,000
Less: Amount representing interest	[1]		(1,070,000)	(1,070,000)
Aircraft and related equipment
Components of short-term borrowings and other debt
Other Notes Payable			8,200,000	8,200,000	14,400,000
Interest Expense, Debt				700,000	800,000
Aircraft and related equipment | Minimum
Components of short-term borrowings and other debt
Interest rate											4.21%
Aircraft and related equipment | Maximum
Components of short-term borrowings and other debt
Interest rate											7.25%
Common Stock Class A
Components of short-term borrowings and other debt
Class of Warrant, Exercise Price of Warrants or Rights | $ / shares												$ 28.72
Convergex Group [Member]
Components of short-term borrowings and other debt
Capital Lease Obligations Incurred			800,000
2022 convertible note [Member] | Convertible Debt
Components of short-term borrowings and other debt
Interest on Convertible Debt, Net of Tax				200,000
Debt Instrument, Convertible, Conversion Price | $ / shares									$ 17.375
Convertible debt, unamortized discount												$ 23,400,000
Amortization of debt discount				200,000
Debt Instrument, Interest Rate, Effective Percentage												7.13%
Debt Issuance Costs, Gross												$ 2,100,000
Debt Instrument, Face Amount									$ 135,000,000
2019 convertible note [Member] | Convertible Debt
Components of short-term borrowings and other debt
Interest rate												3.00%
Principal amount of notes being converted												$ 1,000
Interest on Convertible Debt, Net of Tax				4,300,000	4,500,000	4,500,000
Debt Instrument, Convertible, Conversion Price | $ / shares												$ 21.32
Debt Instrument, Repurchase Amount												$ 115,100,000
Convertible debt, unamortized discount												$ 35,700,000
Amortization of debt discount				7,300,000	6,900,000	6,300,000
Debt Instrument, Interest Rate, Effective Percentage												8.89%
Debt Issuance Costs, Gross												$ 900,000
Extinguishment of Debt, Amount				11,600,000
Debt Instrument, Face Amount												$ 149,500,000
Cash convertible note hedge transaction					20,500,000
Class of Warrant, Exercise Price of Warrants or Rights | $ / shares												$ 28.72
2027 Notes [Member] | Senior Notes
Components of short-term borrowings and other debt
Interest rate										7.35%
Debt Issuance Costs, Gross										$ 5,100,000
Debt Instrument, Face Amount									$ 18,000,000	$ 120,000,000
Interest Expense, Debt, Excluding Amortization				600,000
2021 Notes [Member] | Senior Notes
Components of short-term borrowings and other debt
Extinguishment of Debt, Amount				5,600,000
Debt Instrument, Face Amount			$ 63,250,000	$ 63,250,000
Debt Instrument, Redemption Price, Percentage				106.188%
Interest Expense, Debt, Excluding Amortization				$ 5,300,000	$ 5,200,000	$ 5,200,000
[1]	Amount necessary to reduce net minimum payments to present value calculated at the Company's implicit rate at inception. This amount also includes capitalized debt costs and the unamortized discount on the convertible debt.

Stockholders Equity - Annual (D

Stockholders Equity - Annual (Details) $ / shares in Units, $ in Thousands	Dec. 05, 2016	Dec. 31, 2017USD ($)class$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	May 19, 2015USD ($)$ / sharesshares
Equity, Class of Stock [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.25
Adjustments to Additional Paid in Capital, Stock Split		$ 900
Common stock, shares authorized | shares		125,000,000
Preferred stock, shares authorized | shares		10,000,000	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01
Number of classes | class		2
Proceeds from Issuance of Preferred Stock, net of issuance costs		$ 0	$ 0	$ 117,194
Preferred stock dividends declared		$ 6,792	$ 6,792	4,075
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period | shares		9,810,802
Purchase of treasury stock, shares | shares		1,401,866
Treasury stock, shares, end of period | shares		12,133,276	9,810,802
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period		$ 153,845
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions		11,889	$ 8,835	8,907
Purchase of treasury stock, cost		19,500			$ 300
Treasury stock, cost, end of period		$ 186,846	$ 153,845
Treasury Stock, Average Cost Per Share [Roll Forward]
Treasury stock, average cost per share, beginning of period, in dollars per share | $ / shares		$ 15.68
Purchase of treasury stock, average cost per share, in dollars per share | $ / shares		13.90
Treasury stock, average cost per share, end of period, in dollars per share | $ / shares		$ 15.40	$ 15.68
Convertible Preferred Stock, Shares Issued upon Conversion | shares						38.0619
Convertible Preferred Stock, Threshold Percentage of Stock Price Trigger		150.00%
Treasury Stock
Treasury Stock, Shares [Roll Forward]
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions | shares		822,996
Treasury Stock, Cost [Roll Forward]
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions		$ 11,889
Treasury Stock, Average Cost Per Share [Roll Forward]
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions, Average Cost Per Share | $ / shares		$ 14.45
Treasury stock shares received, other | shares		97,612
Treasury stock received, value, other		$ 1,626
Treasury stock received, per share, other | $ / shares		$ 16.66
Convertible Preferred Stock
Equity, Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage		5.625%
Proceeds from Issuance of Preferred Stock, net of issuance costs			$ 117,200
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs		$ 3,600
Preferred Stock, Liquidation Preference Per Share | $ / shares						$ 1,000
Convertible Preferred Stock | Retained Earnings/(Accumulated deficit)
Equity, Class of Stock [Line Items]
Preferred stock dividends declared		$ 6,792	$ 6,800	$ 4,100
Common Stock Class A
Equity, Class of Stock [Line Items]
Common stock, shares authorized | shares		62,500,000	62,500,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period | shares		9,810,802
Treasury stock, shares, end of period | shares		12,133,276	9,810,802
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period		$ 153,845
Treasury stock, cost, end of period		$ 186,846	$ 153,845
Common Stock Class B
Equity, Class of Stock [Line Items]
Common stock, shares authorized | shares		62,500,000	62,500,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01
Call Option
Equity, Class of Stock [Line Items]
Option indexed to Issuer's Equity, Value						$ 15,900
Maximum
Equity, Class of Stock [Line Items]
Convertible Preferred Stock, Threshold Consecutive Trading Days		30 days
Maximum | Call Option
Equity, Class of Stock [Line Items]
Option Indexed to Issuer's Equity, Strike Price | $ / shares		$ 33.54
Minimum
Equity, Class of Stock [Line Items]
Convertible Preferred Stock, Threshold Consecutive Trading Days		20 days
Minimum | Call Option
Equity, Class of Stock [Line Items]
Option Indexed to Issuer's Equity, Strike Price | $ / shares		$ 26.27

Accumulated Other Comprehens117

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income / (Loss) [Abstract]
Beginning Balance	$ (2)	$ 0	$ 17
Foreign currency translation	(6)	(2)	(17)
Ending Balance	$ (8)	$ (2)	$ 0

Earnings Per Share (Details)

Earnings Per Share (Details) $ / shares in Units, $ in Thousands	Dec. 05, 2016	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Jun. 30, 2017USD ($)$ / sharesshares	Mar. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares		Sep. 30, 2016USD ($)$ / sharesshares		Jun. 30, 2016USD ($)$ / sharesshares		Mar. 31, 2016USD ($)$ / sharesshares		Dec. 31, 2017USD ($)$ / sharesshares		Dec. 31, 2016USD ($)$ / sharesshares		Dec. 31, 2015USD ($)$ / sharesshares		Dec. 31, 2014shares
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.25
Computation of earnings per share:
Net income (loss) | $														$ (37,091)		$ (12,395)		$ 58,975
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds | $		$ (11,621)	$ 5,162	$ 21,145	$ 9,105	$ 9,406		$ 18,478		$ (16,705)		$ (4,297)		23,791		6,882		15,246
Net income (loss) attributable to Cowen Inc. | $		(75,972)	4,666	7,440	2,984	(1,904)		(3,219)		(10,456)		(3,698)		(60,882)		(19,277)		43,729
Preferred stock dividends | $		1,698	1,698	1,698	1,698	1,698		1,698		1,698		1,698		6,792		6,792		4,075
Net income (loss) attributable to Cowen Group, Inc. common stockholders | $		$ (77,670)	$ 2,968	$ 5,742	$ 1,286	$ (3,602)		$ (4,917)		$ (12,154)		$ (5,396)		$ (67,674)		$ (26,069)		$ 39,654
Shares for basic and diluted calculations:
Weighted average shares used in basic computation, shares		30,934,000	31,271,000	28,634,000	27,061,000	26,973,000	[1]	26,993,000	[1]	26,867,000	[1]	26,591,000	[1]	29,492,000	[2]	26,857,000	[2]	27,522,000	[2]
Weighted average shares used in diluted computation, shares		30,934,000	32,246,000	29,474,000	28,401,000	26,973,000	[1]	26,993,000	[1]	26,867,000	[1]	26,591,000	[1]	29,492,000	[2]	26,857,000	[2]	29,043,000	[2]
Earnings (loss) per share:
Earnings Per Share, Basic (in dollars per share) | $ / shares		$ (2.51)	$ 0.09	$ 0.20	$ 0.05	$ (0.13)	[1]	$ (0.18)	[1]	$ (0.45)	[1]	$ (0.20)	[1]	$ (2.29)	[2]	$ (0.97)	[2]	$ 1.44	[2]
Earnings Per Share, Diluted (in dollars per share) | $ / shares		$ (2.51)	$ 0.09	$ 0.19	$ 0.05	$ (0.13)	[1]	$ (0.18)	[1]	$ (0.45)	[1]	$ (0.20)	[1]	$ (2.29)	[2]	$ (0.97)	[2]	$ 1.37	[2]
Stock Options
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares														0		0		3,000
Performance based restricted stock
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares														0		0		65,000
Stock Appreciation Rights
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares														0		0		35,000
Restricted Stock
Shares for basic and diluted calculations:
Shares attributable to share-based payment awards, shares														0		0		1,418,000
Common Stock Class A
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Common stock, shares outstanding, shares		29,632,020				26,731,289								29,632,020		26,731,289		26,401,163		27,922,799
Common stock, restricted shares, shares		191,962				162,176								191,962		162,176
[1]	Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.
[2]	Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.

Segment Reporting (Details)

Segment Reporting (Details)		3 Months Ended								12 Months Ended
		Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)segmentcustomer		Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Entity-Wide Revenue, Major Customer, Number | customer										0
Number of Operating Segments | segment										2
Revenues
Investment banking										$ 223,614,000		$ 133,279,000		$ 222,781,000
Brokerage										293,610,000		199,180,000		157,722,000
Management fees										33,245,000		40,612,000		41,906,000
Incentive income										5,383,000		8,334,000		1,466,000
Investment Income										0		0		0
Interest and dividends										49,440,000		14,732,000		13,796,000
Aircraft lease revenue										3,751,000		4,161,000		0
Reimbursement from affiliates										2,860,000		10,504,000		21,557,000
Reinsurance premiums										30,996,000		32,459,000		0
Other revenue										8,561,000		22,355,000		3,726,000
Total revenues		$ 204,450,000	$ 178,830,000	$ 160,530,000	$ 114,971,000	$ 122,268,000	$ 131,027,000	$ 117,231,000	$ 101,039,000	658,781,000		471,565,000		464,567,000
Expenses
Non-interest expense										684,123,000		508,746,000		475,844,000
Interest and dividends										60,949,000		29,308,000		26,220,000
Total expenses										757,598,000		547,118,000		504,374,000
Other income (loss)
Total other income (loss)										105,779,000		44,066,000		51,286,000
Income tax expense (benefit)		40,646,000	2,281,000	(785,000)	1,911,000	(12,539,000)	8,759,000	(11,992,000)	(3,320,000)	44,053,000		(19,092,000)		(47,496,000)
(Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds										(23,791,000)		(6,882,000)		(15,246,000)
Economic Income (Loss) / Net income (loss) attributable to Cowen Group, Inc.		$ (75,972,000)	$ 4,666,000	$ 7,440,000	$ 2,984,000	$ (1,904,000)	$ (3,219,000)	$ (10,456,000)	$ (3,698,000)	(60,882,000)		(19,277,000)		43,729,000
Consolidated Funds
Revenues
Total revenues										7,321,000		5,949,000		1,613,000
Expenses
Total expenses										12,526,000		9,064,000		2,310,000
Operating Segments
Revenues
Investment banking										223,614,000		133,279,000		222,781,000
Brokerage										312,780,000		207,040,000		160,436,000
Management fees										55,387,000		67,248,000		70,015,000
Incentive income										26,028,000		26,274,000		(1,544,000)
Investment Income										45,142,000		4,023,000		62,596,000
Interest and dividends										0		0		0
Aircraft lease revenue										0		0
Reimbursement from affiliates										0		0		0
Reinsurance premiums										0		0		15,382,000
Other revenue										3,231,000		29,767,000
Total revenues										666,182,000		467,631,000		529,666,000
Expenses
Non-interest expense										625,387,000		471,351,000		469,754,000
Interest and dividends										18,888,000		17,190,000		16,584,000
Total expenses										644,275,000		488,541,000		486,338,000
Other income (loss)
Total other income (loss)										0		0		0
Income tax expense (benefit)										0		0		0
(Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds										(6,072,000)		(7,821,000)		(8,796,000)
Economic Income (Loss) / Net income (loss) attributable to Cowen Group, Inc.										15,835,000		(28,731,000)		34,532,000
Operating Segments | Consolidated Funds
Revenues
Other revenue														0
Total revenues										0		0
Expenses
Total expenses										0		0		0
Operating Segments | Investment Management
Revenues
Investment banking										0		0		0
Brokerage										38,000		0		0
Management fees										52,239,000		64,086,000		68,989,000
Incentive income										26,028,000		26,274,000		(1,544,000)
Investment Income										31,447,000		3,015,000		49,244,000
Interest and dividends										0		0		0
Aircraft lease revenue										0		0
Reimbursement from affiliates										0		0		0
Reinsurance premiums										0		0		14,492,000
Other revenue										1,575,000		29,202,000
Total revenues										111,327,000		122,577,000		131,181,000
Expenses
Non-interest expense										92,567,000		102,163,000		107,291,000
Interest and dividends										14,268,000		12,827,000		11,839,000
Total expenses										106,835,000		114,990,000		119,130,000
Other income (loss)
Total other income (loss)										0		0		0
Income tax expense (benefit)										0		0		0
(Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds										(6,072,000)		(7,821,000)		(8,796,000)
Economic Income (Loss) / Net income (loss) attributable to Cowen Group, Inc.										(1,580,000)		(234,000)		3,255,000
Operating Segments | Investment Management | Consolidated Funds
Revenues
Other revenue														0
Total revenues										0		0
Expenses
Total expenses										0		0		0
Operating Segments | Broker-Dealer
Revenues
Investment banking										223,614,000		133,279,000		222,781,000
Brokerage										312,742,000		207,040,000		160,436,000
Management fees										3,148,000		3,162,000		1,026,000
Incentive income										0		0		0
Investment Income										13,695,000		1,008,000		13,352,000
Interest and dividends										0		0		0
Aircraft lease revenue										0		0
Reimbursement from affiliates										0		0		0
Reinsurance premiums										0		0		890,000
Other revenue										1,656,000		565,000
Total revenues										554,855,000		345,054,000		398,485,000
Expenses
Non-interest expense										532,820,000		369,188,000		362,463,000
Interest and dividends										4,620,000		4,363,000		4,745,000
Total expenses										537,440,000		373,551,000		367,208,000
Other income (loss)
Total other income (loss)										0		0		0
Income tax expense (benefit)										0		0		0
(Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds										0		0		0
Economic Income (Loss) / Net income (loss) attributable to Cowen Group, Inc.										17,415,000		(28,497,000)		31,277,000
Operating Segments | Broker-Dealer | Consolidated Funds
Revenues
Other revenue														0
Total revenues										0		0
Expenses
Total expenses										0		0		0
Adjustments | Funds Consolidation
Revenues
Investment banking										0		0		0
Brokerage										0		0		0
Management fees										(2,593,000)		(1,665,000)		(1,307,000)
Incentive income										(1,739,000)		(714,000)		(736,000)
Investment Income										0		0		0
Interest and dividends										0		0		0
Aircraft lease revenue										0		0
Reimbursement from affiliates										(297,000)		(303,000)		(190,000)
Reinsurance premiums										0		0
Other revenue										0		0		0
Total revenues										2,692,000		3,267,000		(620,000)
Expenses
Non-interest expense										(199,000)		(429,000)		0
Interest and dividends										0		0		0
Total expenses										12,327,000		8,635,000		2,310,000
Other income (loss)
Total other income (loss)										31,073,000		8,532,000		8,781,000
Income tax expense (benefit)										0		0		0
(Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds										(21,438,000)		(3,164,000)		(5,851,000)
Economic Income (Loss) / Net income (loss) attributable to Cowen Group, Inc.										0		0		0
Adjustments | Funds Consolidation | Consolidated Funds
Revenues
Total revenues										7,321,000		5,949,000		1,613,000
Expenses
Total expenses										12,526,000		9,064,000		2,310,000
Adjustments | Other Adjustments
Revenues
Investment banking										0		0		0
Brokerage										(19,170,000)	[1]	(7,860,000)	[1]	(2,714,000)
Management fees	[2]									(19,549,000)		(24,971,000)		(26,802,000)
Incentive income	[2]									(18,906,000)		(17,226,000)		3,746,000
Investment Income	[4]									(45,142,000)	[3]	(4,023,000)	[3]	(62,596,000)
Interest and dividends	[4]									49,440,000		14,732,000		13,796,000
Aircraft lease revenue	[3]									3,751,000		4,161,000
Reimbursement from affiliates	[5]									3,157,000		10,807,000		21,747,000
Reinsurance premiums	[6]									30,996,000		32,459,000
Other revenue										5,330,000	[6]	(7,412,000)	[6]	(11,656,000)	[4]
Total revenues										(10,093,000)		667,000		(64,479,000)
Expenses
Non-interest expense	[7],[8]									58,935,000		37,824,000		6,090,000	[4]
Interest and dividends	[4]									42,061,000		12,118,000		9,636,000
Total expenses										100,996,000		49,942,000		15,726,000
Other income (loss)
Total other income (loss)										74,706,000	[1],[9],[10]	35,534,000	[4]	42,505,000	[4]
Income tax expense (benefit)	[7]									44,053,000		(19,092,000)		(47,496,000)
(Income) loss attributable to redeemable non-controlling interests in consolidated subsidiaries and funds										3,719,000		4,103,000		(599,000)
Economic Income (Loss) / Net income (loss) attributable to Cowen Group, Inc.										(76,717,000)		9,454,000		9,197,000
Adjustments | Other Adjustments | Consolidated Funds
Revenues
Total revenues										0		0		0
Expenses
Total expenses										$ 0		$ 0		$ 0
[1]	Economic Income (Loss) brokerage revenues included net securities borrowed and securities loaned activities.
[2]	Economic Income (Loss) recognizes revenues (i) net of distribution fees paid to agents and (ii) our proportionate share of management and incentive fees of certain real estate operating entities, the healthcare royalty business and the activist business.
[3]	Aircraft lease revenue is shown net of expenses in investment income for Economic Income (Loss).
[4]	Economic Income (Loss) recognizes Company income from proprietary trading (including interest and dividends).
[5]	Reimbursement from affiliates is shown as a reduction of Economic Income expenses, but is included as a part of revenues under US GAAP.
[6]	Economic Income (Loss) recognizes underwriting income from the Company's insurance related activities, net of expenses, within other revenue.
[7]	Economic Income (Loss) excludes income taxes and acquisition related adjustments as management does not consider these items when evaluating the performance of the segment.
[8]	Economic Income (Loss) recognizes the Company's proportionate share of expenses, for certain real estate operating entities and the activist business, for which the investments are recorded under the equity method of accounting for investments.
[9]	Economic Income (Loss) excludes gain / (loss) on debt extinguishment.
[10]	Economic Income (Loss) excludes the bargain purchase gain which resulted from the Convergex Group acquisition.

Regulatory Requirements (Detail

Regulatory Requirements (Details)	12 Months Ended
	Dec. 31, 2017USD ($)
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum Net Capital Required	$ 250,000
Cowen and Company
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	1,000,000
Net capital	40,200,000
Excess capital	39,200,000
Cowen Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Cash and Securities Segregated under Securities Exchange Commission Regulation	20,300,000
Net capital requirement under alternative method	2,700,000
Required Net Capital under Commodity Exchange Act	108,700,000
Net capital	111,400,000
Excess capital	108,700,000
ATM Execution LLC
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	300,000
Net capital	1,000,000
Excess capital	700,000
Cowen Prime
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	300,000
Net capital	12,300,000
Excess capital	12,000,000
Westminster Research
Regulatory Requirements for Broker-Dealers [Line Items]
Net capital requirement under alternative method	300,000
Net capital	7,600,000
Excess capital	7,300,000
RCG Insurance Company
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum Net Capital Required	300,000
Net capital	28,700,000
Options Clearing Corporation [Member] | Cowen Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Minimum Net Capital Required	$ 2,000,000
Minimum net capital required, percent	2.00%
U.K. Financial Services Authority | Ramius U.K., Ltd.
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	$ 200,000
Financial resources requirement	100,000
Excess financial resources	100,000
U.K. Financial Services Authority | Cowen International Limited
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	11,500,000
Financial resources requirement	7,100,000
Excess financial resources	4,400,000
U.K. Financial Services Authority | Cowen Execution Services Ltd
Regulatory Requirements for Broker-Dealers [Line Items]
Financial resources	3,800,000
Financial resources requirement	2,600,000
Excess financial resources	1,200,000
Minimum | Cowen Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Cash and Securities Segregated under Securities Exchange Commission Regulation	10,500,000
Required Net Capital under Commodity Exchange Act	45,000
Special Reserve Accounts [Member] | Cowen Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Cash and Securities Segregated under Securities Exchange Commission Regulation	29,700,000
Special Reserve Accounts [Member] | Minimum | Cowen Execution
Regulatory Requirements for Broker-Dealers [Line Items]
Cash and Securities Segregated under Securities Exchange Commission Regulation	$ 17,100,000

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Fees receivable, net of allowance of $1,736 and $0, respectively	$ 111,784				$ 45,883				$ 111,784	$ 45,883
Reimbursable to affiliated funds	100								200
Interest Income, Related Party									100
Due from related parties	34,814				39,629				34,814	39,629
Redeemable non-controlling interests, Related Party	440,604				379,205				440,604	379,205
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds	11,621	$ (5,162)	$ (21,145)	$ (9,105)	(9,406)	$ (18,478)	$ 16,705	$ 4,297	(23,791)	(6,882)	$ (15,246)
Employees
Related Party Transaction [Line Items]
Redeemable non-controlling interests, Related Party	28,200				32,900				28,200	32,900
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds									(7,200)	(5,700)	(10,400)
Employee Loans
Related Party Transaction [Line Items]
Due from employees	11,100				9,200				11,100	9,200
Forgivable Loan Balances	4,800				3,300				4,800	3,300
Amortization on Forgivable Loans									$ 2,100	1,200	$ 3,200
Employee Loans | Minimum
Related Party Transaction [Line Items]
Forgivable Loans, Vesting Period									1 year
Employee Loans | Maximum
Related Party Transaction [Line Items]
Forgivable Loans, Vesting Period									3 years
Affiliated Entity
Related Party Transaction [Line Items]
Fees receivable, net of allowance of $1,736 and $0, respectively	13,500				12,600				$ 13,500	12,600
Affiliated Entity | Fees Payable
Related Party Transaction [Line Items]
Fees payable to related parties					300					300
Investor
Related Party Transaction [Line Items]
Due to Affiliate	600				700				600	700
Other Funds
Related Party Transaction [Line Items]
Due from related parties	9,700				11,800				9,700	$ 11,800
Starboard Value LP
Related Party Transaction [Line Items]
Effective interest rate										5.00%
Interest Income, Related Party									800	$ 600
Due from related parties	$ 14,000				$ 18,700				$ 14,000	$ 18,700
Finance Period									5 years

Guarantees and Off-Balance S122

Guarantees and Off-Balance Sheet Arrangements (Details)	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Letter of credit, borrowing capacity	$ 180,000,000
Line of Credit Facility, Remaining Borrowing Capacity	180,000,000
Pledge Lines
Debt Instrument [Line Items]
Letter of credit, borrowing capacity	150,000,000
Line of Credit Facility, Remaining Borrowing Capacity	150,000,000
BMO Harris Bank [Member] | Pledge Lines
Debt Instrument [Line Items]
Letter of credit, borrowing capacity	150,000,000
Line of Credit Facility, Remaining Borrowing Capacity	150,000,000
BMO Harris Bank [Member] | Revolving Credit Facility
Debt Instrument [Line Items]
Letter of credit, borrowing capacity	30,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 30,000,000

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - Subsequent Event [Member] $ in Millions	Feb. 13, 2018USD ($)
Subsequent Event [Line Items]
Stock Repurchase Program, Additional Authorized Amount	$ 23.6
Stock Repurchase Program, Authorized Amount	$ 25

Supplemental Financial Infor124

Supplemental Financial Information (Details) $ / shares in Units, shares in Thousands, $ in Thousands	Dec. 05, 2016	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares	Jun. 30, 2017USD ($)$ / sharesshares	Mar. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares		Sep. 30, 2016USD ($)$ / sharesshares		Jun. 30, 2016USD ($)$ / sharesshares		Mar. 31, 2016USD ($)$ / sharesshares		Dec. 31, 2017USD ($)$ / sharesshares		Dec. 31, 2016USD ($)$ / sharesshares		Dec. 31, 2015USD ($)$ / sharesshares
Quarterly Financial Information Disclosure [Abstract]
Stockholders' Equity Note, Stock Split, Conversion Ratio	0.25
Total revenues		$ 204,450	$ 178,830	$ 160,530	$ 114,971	$ 122,268		$ 131,027		$ 117,231		$ 101,039		$ 658,781		$ 471,565		$ 464,567
Income (loss) before income taxes		(46,947)	12,109	27,800	14,000	(5,037)		24,018		(39,153)		(11,315)		6,962		(31,487)		11,479
Income tax expense (benefit)		40,646	2,281	(785)	1,911	(12,539)		8,759		(11,992)		(3,320)		44,053		(19,092)		(47,496)
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest		(87,593)	9,828	28,585	12,089	7,502		15,259		(27,161)		(7,995)
Net income (loss) attributable to redeemable non-controlling interests in consolidated subsidiaries and funds		(11,621)	5,162	21,145	9,105	9,406		18,478		(16,705)		(4,297)		23,791		6,882		15,246
Net income (loss) attributable to Cowen Inc.		(75,972)	4,666	7,440	2,984	(1,904)		(3,219)		(10,456)		(3,698)		(60,882)		(19,277)		43,729
Preferred stock dividends		1,698	1,698	1,698	1,698	1,698		1,698		1,698		1,698		6,792		6,792		4,075
Net income (loss) attributable to Cowen Group, Inc. common stockholders		$ (77,670)	$ 2,968	$ 5,742	$ 1,286	$ (3,602)		$ (4,917)		$ (12,154)		$ (5,396)		$ (67,674)		$ (26,069)		$ 39,654
Earnings (loss) per share:
Earnings Per Share, Basic (in dollars per share) | $ / shares		$ (2.51)	$ 0.09	$ 0.20	$ 0.05	$ (0.13)	[1]	$ (0.18)	[1]	$ (0.45)	[1]	$ (0.20)	[1]	$ (2.29)	[2]	$ (0.97)	[2]	$ 1.44	[2]
Earnings Per Share, Diluted (in dollars per share) | $ / shares		$ (2.51)	$ 0.09	$ 0.19	$ 0.05	$ (0.13)	[1]	$ (0.18)	[1]	$ (0.45)	[1]	$ (0.20)	[1]	$ (2.29)	[2]	$ (0.97)	[2]	$ 1.37	[2]
Weighted average common shares outstanding:
Basic (in shares) | shares		30,934	31,271	28,634	27,061	26,973	[1]	26,993	[1]	26,867	[1]	26,591	[1]	29,492	[2]	26,857	[2]	27,522	[2]
Diluted (in shares) | shares		30,934	32,246	29,474	28,401	26,973	[1]	26,993	[1]	26,867	[1]	26,591	[1]	29,492	[2]	26,857	[2]	29,043	[2]
[1]	Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.
[2]	Share and per share amounts have been retroactively updated to reflect the one-for-four reverse stock split effective as of December 5, 2016.

Uncategorized Items - cown-2017

Label	Element	Value
Convertible Preferred Stock [Member]
Stock Issued During Period, Shares, Other	us-gaap_StockIssuedDuringPeriodSharesOther	120,750