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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Class of Stock [Line Items]
Common stock, shares issued under dividend reinvestment program	273	265	543	550
Class A Common Stock [Member]
Class of Stock [Line Items]
Deferred stock units held by directors	181,931	155,676	181,931	155,676
Common stock, shares issued under dividend reinvestment program			543	550