Equity - Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units (Parenthetical) (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Class of Stock [Line Items]
Common stock, shares issued under dividend reinvestment program	428	262	971	812
Class A Common Stock [Member]
Class of Stock [Line Items]
Deferred stock units held by directors	189,587	162,371	189,587	162,371
Common stock, shares issued under dividend reinvestment program			971	812