Stock Transactions and Unit Redemptions - Changes in Shares of Class A Common Stock Outstanding (Detail) - shares	1 Months Ended			3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2017	May 31, 2017	Apr. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Share issuances:
Treasury stock repurchases	(27,634)	(121,023)	(248,882)		(552,955)		(950,494)
Forfeitures of restricted Class A common stock							(36,000)	(16,000)
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares outstanding at beginning of period			248,466,750	248,466,750	244,869,624	236,749,861	244,869,624	219,063,365	219,063,365
Share issuances:
Exchanges of limited partnership interests				1,950,465		2,427,152	5,361,137	3,321,754	8,705,906
Issuance of Class A common stock for general corporate purposes						1,648,000		1,648,000
Vesting of restricted stock units (RSUs)				80,629		113,572	437,018	487,471
Acquisitions				968,705		1,147,516	1,341,783	24,729,033
Other issuances of Class A common stock				23,674		15,079	33,616	42,305
Treasury stock repurchases				(397,539)		(797,189)	(950,494)	(7,984,235)	(10,823,942)
Forfeitures of restricted Class A common stock				(35,598)		(11,958)	(35,598)	(15,660)	(59,317)
Shares outstanding at end of period	251,057,086			251,057,086	248,466,750	241,292,033	251,057,086	241,292,033	244,869,624