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Stock Transactions and Unit Redemptions - Changes in Shares of Class A Common Stock Outstanding (Detail) - shares
1 Months Ended 3 Months Ended
Mar. 31, 2019
Mar. 31, 2019
Mar. 31, 2018
Share issuances:      
Treasury stock repurchases (233,172) (233,172)  
Class A Common Stock [Member]      
Class of Stock [Line Items]      
Shares outstanding at beginning of period   291,474,768 256,968,372
Share issuances:      
Redemptions/Exchanges of limited partnership interests   1,820,588 2,787,190
Vesting of restricted stock units (RSUs)   240,335 280,884
Acquisition related issuances   18,217 317,096
Other issuances of Class A common stock   61,642 22,644
Issuance of Class A common stock for general corporate purposes     17,923,714
Deferred stock awards     979,344
Treasury stock repurchases   (233,172) 0
Shares outstanding at end of period 293,382,378 293,382,378 279,279,244