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