Stockholders' Equity Stockholders Equity Annual Disclosures (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014 class	Dec. 31, 2013	Dec. 31, 2012
Equity, Class of Stock [Line Items]
Common stock, shares authorized	500,000,000us-gaap_CommonStockSharesAuthorized
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period	15,873,549us-gaap_TreasuryStockShares
Treasury stock, shares, end of period	23,507,656us-gaap_TreasuryStockShares	15,873,549us-gaap_TreasuryStockShares
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period	$ 48,084us-gaap_TreasuryStockValue
Shares purchased for minimum tax withholding, cost	5,649	3,649	3,988
Treasury stock reissued, cost	0
Treasury stock, cost, end of period	79,771us-gaap_TreasuryStockValue	48,084us-gaap_TreasuryStockValue
Treasury Stock, Average Cost Per Share [Roll Forward]
Number of classes	2cown_NumberOfClasses
Preferred stock, shares authorized	10,000,000us-gaap_PreferredStockSharesAuthorized	10,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Treasury Stock
Treasury Stock, Shares [Roll Forward]
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions	1,376,236
Treasury stock reissued, shares	0	(24,744)
Purchase of treasury stock, shares	6,257,871
Treasury Stock, Cost [Roll Forward]
Shares purchased for minimum tax withholding, cost	5,649
Treasury stock reissued, cost		(90)
Purchase of treasury stock, cost	26,038
Treasury Stock, Average Cost Per Share [Roll Forward]
Treasury stock, average cost per share, beginning of period, in dollars per share	$ 3.03
Shares purchased for minimum tax withholding, average cost per share, in dollars per share	$ 4.10
Treasury stock reissued, average cost per share, in dollars per share	$ 0.00
Purchase of treasury stock, average cost per share, in dollars per share	$ 4.16
Treasury stock, average cost per share, end of period, in dollars per share	$ 3.39	$ 3.03
Common Stock Class A
Equity, Class of Stock [Line Items]
Common stock, shares authorized	250,000,000	250,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, end of period	23,507,656	15,873,549
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, end of period	$ 79,771	$ 48,084
Common Stock Class B
Equity, Class of Stock [Line Items]
Common stock, shares authorized	250,000,000	250,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01

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Shares Paid for Tax Withholding for Share Based Compensation, Average Cost Per Share

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Treasury Stock, Average Price Per Share

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Total cost of treasury stock reissued divided by the total number of shares reissued.

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Treasury Stock, Shares, Acquired, Cost Method, Excluding Adjustments Related to Tax Withholding for Share-based Compensation

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Treasury Stock, Value, Acquired, Cost Method, Excluding Adjustments Related to Tax Withholding for Share-based Compensation

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The amount of adjustment to stockholders' equity associated with an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding.

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Equity impact of the value of treasury stock (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding.

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Total cost of shares repurchased divided by the total number of shares repurchased.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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The amount allocated to treasury stock. Treasury stock is common and preferred shares of an entity that were issued, repurchased by the entity, and are held in its treasury.

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