Stock Transactions and Unit Redemptions - Unit Redemption and Share Repurchase Activity (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Thousands					3 Months Ended				12 Months Ended
	Feb. 24, 2016	Jan. 30, 2015	Feb. 05, 2014	Jan. 21, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Average price for redemption of limited partnership units									$ 9.09	$ 8.86
Repurchase of Class A common stock, shares Treasury Stock Shares Acquired					1,497,760	1,341,947	797,189	7,187,046	10,823,942
Aggregate purchase price of Class A common stock									$ 96,025	$ 12,114	$ 100,268
Average price of Class A common stock					$ 9.59	$ 8.90	$ 9.04	$ 8.72	$ 8.88
Class A Common Stock [Member]
Class of Stock [Line Items]
Repurchase of Class A common stock, shares Treasury Stock Shares Acquired			636,841						10,823,942	1,416,991	13,630,725
Aggregate purchase price of Class A common stock									$ 96,000	$ 12,100
Average price of Class A common stock	$ 8.40	$ 7.83	$ 6.51	$ 6.51					$ 8.88	$ 8.55
Limited Partnership [Member]
Class of Stock [Line Items]
Redeemed limited partnership units									7,200,000	7,500,000
Aggregate redemption price of limited partnership units									$ 65,700	$ 66,300
Other Ownership Interest [Member]
Class of Stock [Line Items]
Redeemed limited partnership units									319,200	100,000
Average price for redemption of founding/working partner units									$ 8.64	$ 8.44
Aggregate redemption price of limited partnership units									$ 2,800	$ 800