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
Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Common stock, shares issued under dividend reinvestment program	270	285
Class A Common Stock [Member]
Class of Stock [Line Items]
Deferred stock units held by directors	175,442	148,843
Common stock, shares issued under dividend reinvestment program	270	285

Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Name:	us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration