Stock Transactions and Unit Redemptions - Changes in Shares of Class A Common Stock Outstanding (Detail) - shares	1 Months Ended			3 Months Ended		12 Months Ended
	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Share issuances:
Treasury stock repurchases	(27,039)	(98,660)	(427,256)	(552,955)
Forfeitures of restricted Class A common stock				0	(3,700)
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares outstanding at beginning of period			244,869,624	244,869,624	219,063,365	219,063,365
Share issuances:
Exchanges of limited partnership interests				3,410,672	894,602	8,705,906
Vesting of restricted stock units (RSUs)				356,389	373,899
Acquisitions				373,078	23,581,517
Other issuances of Class A common stock				9,942	27,226
Treasury stock repurchases				(552,955)	(7,187,046)	(10,823,942)
Forfeitures of restricted Class A common stock					(3,702)	(59,317)
Shares outstanding at end of period	248,466,750			248,466,750	236,749,861	244,869,624