Significant Accounting Policies (Details) $ in Millions |
Feb. 01, 2018 |
Sep. 30, 2018
USD ($)
|
Dec. 31, 2017
USD ($)
|
|---|---|---|---|
| Retroactive Adjustments for Common Stock Split | |||
| Stock split | 175.194 | ||
| Variable Interest Entities | |||
| Maximum risk of loss related to unconsolidated sponsored VIE investment funds | $ 14.1 | $ 10.9 | |
| Cerebellum Capital, LLC | |||
| Variable Interest Entities | |||
| Maximum risk of loss related to unconsolidated sponsored VIE investment funds | 8.0 | 6.0 | |
| Maximum exposure, put option | 1.0 | ||
| Investment in unconsolidated VIE and maximum exposure, investment | $ 8.0 | $ 5.0 |