Equity	12 Months Ended
Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Equity	Note 11 — 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. In connection with the recapitalization, in October 2017 the Company borrowed $350 million of secured term loans and repaid $83.8 million outstanding under the existing bank loan facilities. See “Note 10 — Loan Facilities”. In October 2017, the Company repurchased 3,434,137 shares of its common stock under the share repurchase plan through a tender offer at $17.25 per share for a total cash cost of approximately $59.2 million. In addition, the Company incurred fees and expenses relating to the tender offer of $0.7 million. In addition, during November and December 2017, the Company repurchased an additional 343,411 common shares through other open market transactions. Since commencement of its share repurchase plan, the Company repurchased in aggregate 3,777,548 shares of its common stock at an average price of $17.41 for a total cost of $65.8 million. At December 31, 2017, the Company had remaining authorization under its share repurchase plan of $219.2 million. See "Note 19 — Subsequent Events". In November 2017, the Company's Chairman, through an entity controlled by him, and the Company's Chief Executive Officer, in his personal capacity and through an entity controlled by him, each purchased of $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. See "Note 9 — Related Parties". 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 will issue 334,048 shares of common stock shortly after the second or fourth anniversary of the Acquisition, as the case may be, if the revenue target related to the Earnout is achieved. If the revenue target related to the Earnout is not achieved the common shares will not be issued. The fair value of the contingent issuance of common shares was valued on the date of the acquisition at $11.9 million and has been recorded as additional paid in capital in the consolidated statements of financial condition. A portion of the value will be transferred to common stock if the Earnout is achieved. See "Note 3 — Acquisition" and "Note 12 — Earnings per Share". During 2017, 1,197,260 restricted stock units vested and were issued as common stock of which the Company is deemed to have repurchased 491,677 shares at an average price of $28.04 per share in conjunction with the payment of tax liabilities in respect of stock delivered to its employees in settlement of restricted stock units. During 2016, 852,218 restricted stock units vested and were issued as common stock of which the Company is deemed to have repurchased 319,573 shares at an average price of $25.10 per share in conjunction with the payment of tax liabilities in respect of stock delivered to its employees in settlement of restricted stock units. In addition, during 2016 the Company repurchased in open market transactions 891,017 shares of its common stock at an average price of $22.63. On December 20, 2017, a dividend of $0.05 per share was paid to stockholders of record on December 6, 2017. For the year ended December 31, 2017, dividends declared per common share were $1.40. For each of the years ended December 31, 2016 and 2015, dividends declared per common share were $1.80 and are paid on outstanding common shares. In addition, dividend equivalent amounts are paid on outstanding restricted stock units and amounted to $6.3 million, $8.5 million and $6.5 million for the years ended December 31, 2017, 2016 and 2015, respectively, and are included in dividends paid on the consolidated statements of cash flows. In the event a restricted stock unit holder’s employment is terminated, 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. See “Note 14 — Deferred Compensation - Restricted Stock Units”.

Note 11 — 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. In connection with the recapitalization, in October 2017 the Company borrowed $350 million of secured term loans and repaid $83.8 million outstanding under the existing bank loan facilities. See “Note 10 — Loan Facilities”.

In October 2017, the Company repurchased 3,434,137 shares of its common stock under the share repurchase plan through a tender offer at $17.25 per share for a total cash cost of approximately $59.2 million. In addition, the Company incurred fees and expenses relating to the tender offer of $0.7 million. In addition, during November and December 2017, the Company repurchased an additional 343,411 common shares through other open market transactions. Since commencement of its share repurchase plan, the Company repurchased in aggregate 3,777,548 shares of its common stock at an average price of $17.41 for a total cost of $65.8 million. At December 31, 2017, the Company had remaining authorization under its share repurchase plan of $219.2 million. See "Note 19 — Subsequent Events".

In November 2017, the Company's Chairman, through an entity controlled by him, and the Company's Chief Executive Officer, in his personal capacity and through an entity controlled by him, each purchased of $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. See "Note 9 — Related Parties".

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 will issue 334,048 shares of common stock shortly after the second or fourth anniversary of the Acquisition, as the case may be, if the revenue target related to the Earnout is achieved. If the revenue target related to the Earnout is not achieved the common shares will not be issued. The fair value of the contingent issuance of common shares was valued on the date of the acquisition at $11.9 million and has been recorded as additional paid in capital in the consolidated statements of financial condition. A portion of the value will be transferred to common stock if the Earnout is achieved. See "Note 3 — Acquisition" and "Note 12 — Earnings per Share".

During 2017, 1,197,260 restricted stock units vested and were issued as common stock of which the Company is deemed to have repurchased 491,677 shares at an average price of $28.04 per share in conjunction with the payment of tax liabilities in respect of stock delivered to its employees in settlement of restricted stock units.

During 2016, 852,218 restricted stock units vested and were issued as common stock of which the Company is deemed to have repurchased 319,573 shares at an average price of $25.10 per share in conjunction with the payment of tax liabilities in respect of stock delivered to its employees in settlement of restricted stock units. In addition, during 2016 the Company repurchased in open market transactions 891,017 shares of its common stock at an average price of $22.63.

On December 20, 2017, a dividend of $0.05 per share was paid to stockholders of record on December 6, 2017. For the year ended December 31, 2017, dividends declared per common share were $1.40. For each of the years ended December 31, 2016 and 2015, dividends declared per common share were $1.80 and are paid on outstanding common shares. In addition, dividend equivalent amounts are paid on outstanding restricted stock units and amounted to $6.3 million, $8.5 million and $6.5 million for the years ended December 31, 2017, 2016 and 2015, respectively, and are included in dividends paid on the consolidated statements of cash flows. In the event a restricted stock unit holder’s employment is terminated, 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. See “Note 14 — Deferred Compensation - Restricted Stock Units”.