Equity	12 Months Ended
Equity	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Equity	Note 10 — Equity In September 2017, the Company announced plans for a leveraged recapitalization, which included the authorization to repurchase up to $285 million of the Company’s common stock. As part of the refinancing in April 2019, the amount permitted and authorized for future share repurchases was increased to $339.1 million, or by $75.0 million from the amount repurchased in advance of the refinancing. During the year ended December 31, 2019, the Company repurchased 3,275,641 shares of common stock through open market transactions at an average price of $16.93 per share, for a total cost of $55.5 million. During the year ended December 31, 2018, the Company repurchased 7,497,635 shares of common stock through a modified Dutch auction tender and open market transactions at an average price of $24.89 per share, for a total cost of $186.6 million. During the year ended December 31, 2017, the Company repurchased 3,777,548 shares of common stock through a tender offer and other open market transactions at an average price of $17.41 per share, for a total cost of $65.8 million. In addition, the Company incurred fees and expenses relating to tender offers of $0.2 million and $0.7 million during the years ended December 31, 2018 and 2017, respectively. As of December 31, 2019, the Company has repurchased under the recapitalization plan 14,550,824 shares of common stock at an average price of $21.16 per share for a total cost of $307.9 million and had $31.2 million remaining and authorized under its repurchase plan. In November 2017, the Company's then Chairman, through an entity controlled by him, and the Company's now Chairman and Chief Executive Officer, in his personal capacity and through an entity controlled by him, each purchased $10.0 million of the Company’s common stock, for an aggregate total of $20.0 million, and a total of 1,159,420 common shares were issued. In connection with the acquisition of Cogent, the Company issued 779,454 shares of common stock on the acquisition date, April 1, 2015. In addition, the Company issued 334,048 shares of common stock shortly after the revenue target for the second two year period ended March 31, 2019 was achieved. The fair value of the contingent issuance of common shares was valued on the date of the acquisition at $11.9 million and was recorded as additional paid in capital in the consolidated statements of financial condition. Upon delivery of the shares in April 2019, the par value of the shares was transferred to common stock in the consolidated statement of financial condition. In addition, $1.2 million was reflected as an adjustment to additional paid-in capital in the consolidated statement of financial condition for the tax effect of the difference in the acquisition date value of the contingently issuable shares and the fair value of the shares when issued in April 2019. See “Note 7 — Fair Value of Financial Instruments” and “Note 11 — Earnings per Share”. During 2019, 1,407,095 restricted stock units vested and were settled in shares of common stock, of which the Company is deemed to have repurchased 573,472 shares at an average price of $24.37 per share for a total cost of $14.0 million in conjunction with the payment of tax liabilities in respect of stock delivered to its employees in settlement of restricted stock units. During 2018, 1,238,733 restricted stock units vested and were settled in shares of common stock, of which the Company is deemed to have repurchased 433,507 shares at an average price of $20.00 per share for a total cost of $8.7 million in conjunction with the payment of tax liabilities in respect of stock delivered to its employees in settlement of restricted stock units. Dividends declared and paid on outstanding common share were $0.20, $0.20 and $1.40 for each of the years ended December 31, 2019, 2018 and 2017, respectively. In addition, dividend equivalent amounts are accrued and paid on outstanding restricted stock units and amounted to $1.3 million, $1.1 million and $6.3 million for the years ended December 31, 2019, 2018 and 2017, respectively, and paid amounts are included in dividends paid on the consolidated statements of cash flows. In the event a restricted stock unit holder’s employment is terminated, to the extent dividends have been paid to the holder, a portion of the dividend equivalent amount is required to be paid back (a “clawback”) to the Company and is netted against the dividend equivalent amounts herein. See “Note 13 — Deferred Compensation — Restricted Stock Units”.