Equity - Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units (Parenthetical) (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Class A Common Stock [Member]
Class of Stock [Line Items]
Restricted Class A Common Stock, Forfeited	879	17,565	17,820
Class A Common Stock [Member]
Class of Stock [Line Items]
Deferred stock units held by directors	306,691	260,066	228,839
Common stock, shares issued under dividend reinvestment program	2,050	1,214	1,688