Retirement Plan	12 Months Ended
Dec. 31, 2017
Retirement Benefits [Abstract]
Retirement Plan	Note 13 — Retirement Plan In the U.S., the Company sponsor qualified defined contribution plans (the “Retirement Plans”) covering all eligible employees of G&Co and GC LP The Retirement Plans provide for both employee contributions in accordance with Section 401(k) of the Internal Revenue Code, and employer discretionary profit sharing contributions, subject to statutory limits. The Company incurred costs of $0.6 million, $0.6 million and $0.3 million for contributions to the Retirement Plans for the years ended December 31, 2017, 2016 and 2015, respectively. There was $0.2 million and $0.5 million related to contributions due to the Retirement Plans included in compensation payable at December 31, 2017 and 2016, respectively. GCI also operates a defined contribution pension fund for its employees. The assets of the pension fund are held separately in an independently administered fund. For the years ended December 31, 2017, 2016 and 2015, GCI incurred costs for the funding of pension contributions of approximately $0.3 million, $0.4 million and $0.5 million, respectively. At December 31, 2017 and 2016, there were no amounts related to contributions due to the defined contribution pension fund included in compensation payable. Greenhill Australia is required by Australian law to contribute compulsory superannuation on employees' gross earnings, generally at a rate of 9%, subject to an annual limit per employee. Superannuation is a defined contribution plan in which retirement benefits are determined by the contribution accumulated over the working life plus investment earnings within the fund less expenses. Greenhill Australia incurred costs for the funding of pension contributions of approximately $0.4 million for each of the years ended December 31, 2017 and 2016, respectively, and $0.5 million for the year ended December 31, 2015. At December 31, 2017 and 2016, there were no amounts related to superannuation contributions due to the defined contribution plan included in compensation payable.

Note 13 — Retirement Plan

In the U.S., the Company sponsor qualified defined contribution plans (the “Retirement Plans”) covering all eligible employees of G&Co and GC LP The Retirement Plans provide for both employee contributions in accordance with Section 401(k) of the Internal Revenue Code, and employer discretionary profit sharing contributions, subject to statutory limits. The Company incurred costs of $0.6 million, $0.6 million and $0.3 million for contributions to the Retirement Plans for the years ended December 31, 2017, 2016 and 2015, respectively. There was $0.2 million and $0.5 million related to contributions due to the Retirement Plans included in compensation payable at December 31, 2017 and 2016, respectively.

GCI also operates a defined contribution pension fund for its employees. The assets of the pension fund are held separately in an independently administered fund. For the years ended December 31, 2017, 2016 and 2015, GCI incurred costs for the funding of pension contributions of approximately $0.3 million, $0.4 million and $0.5 million, respectively. At December 31, 2017 and 2016, there were no amounts related to contributions due to the defined contribution pension fund included in compensation payable.

Greenhill Australia is required by Australian law to contribute compulsory superannuation on employees' gross earnings, generally at a rate of 9%, subject to an annual limit per employee. Superannuation is a defined contribution plan in which retirement benefits are determined by the contribution accumulated over the working life plus investment earnings within the fund less expenses. Greenhill Australia incurred costs for the funding of pension contributions of approximately $0.4 million for each of the years ended December 31, 2017 and 2016, respectively, and $0.5 million for the year ended December 31, 2015. At December 31, 2017 and 2016, there were no amounts related to superannuation contributions due to the defined contribution plan included in compensation payable.