Stock Transactions and Unit Redemptions - Change in Shares of Class A Common Stock Outstanding (Parenthetical) (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Apr. 01, 2010
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued for general corporate purposes	0	0	0	0
8.75% Convertible Notes [Member]
Class of Stock [Line Items]
Convertible notes rate	8.75%		8.75%		8.75%	8.75%
8.75% Convertible Notes [Member] | Class A Common Stock [Member]
Class of Stock [Line Items]
Convertible notes rate	8.75%		8.75%