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	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Deferred stock units held by directors	244,536	213,136
Common stock, shares issued under dividend reinvestment program	553	876