Equity - Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units (Parenthetical) (Detail) - Class A Common Stock [Member] - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Class of Stock [Line Items]
Deferred stock units held by directors	252,267	220,947
Common stock, shares issued under dividend reinvestment program	879	1,279