Unconsolidated Entities - Summary of Amounts Recognized in Consolidated Statements of Income Related to Co-Investment Ventures (Parenthetical) (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Equity Method Investments And Joint Ventures [Abstract] | |||
| Earned promote revenue | $ 127.5 | $ 88.5 | $ 29.5 |