Deferred Compensation Arrangement with Individual, Interest Rate

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- Definition

Deferred Compensation Arrangement with Individual, Total Compensation Cost Not yet Recognized

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- Definition

Deferred cash award granted

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- Definition

Percent of RSU's earned

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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- Definition

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Net number of non-option equity instruments granted to participants.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Number of shares issued under share-based payment arrangement.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Share-Based Compensation and Employee Ownership Plans Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Apr. 30, 2019	Mar. 31, 2016	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jul. 21, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted			0		0
Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted							3,000,000.0
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of RSU's earned					0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of RSU's earned					200.00%
Equity Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-compensation expense recognized in connection with compensation plan			$ 15.3	$ 9.4	$ 23.6	$ 17.2
Tax benefit of stock-compensation expense recognized in connection with compensation plan			3.5	$ 2.0	$ 5.3	$ 4.2
Equity Plans \| Restricted Shares and Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares					2,268,759	2,194,230
Vested, shares					1,290,624	1,282,843
Forfeited, shares					35,441	153,399
Unrecognized compensation expense			$ 81.7		$ 81.7
Period for recognition					2 years 5 months 23 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number			6,219,832	6,486,950	6,219,832	6,486,950		5,364,486	5,962,295
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 \| Restricted Stock Units (RSUs) \| Non-employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares			0	0	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period					79,487
Equity Plans \| Performance based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares	1,033,333	1,033,333
Vested, shares					145,986
Forfeited, shares					320,681
Equity Plans \| Employee Stock \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period					2 years
Equity Plans \| Employee Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period					5 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period					7 years
Deferred Cash Award \| Cowen Group, Inc. 2010 Equity and Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation award, vesting period					4 years
Deferred cash awards granted					$ 50.2
Deferred cash award, interest rate					0.70%
Deferred cash awards, unrecognized compensation expense			$ 89.5		$ 89.5