Summary of Weighted-Average Units and Shares Outstanding (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Operating Partnership Units
Weighted-average Units outstanding
Weighted Average General Partnership Units Outstanding	11,419,777	11,938,420	11,478,543	8,221,330
Common Stock
Weighted-average Units outstanding
Weighted Average General Partnership Units Outstanding	47,213,612	37,271,714	43,576,705	32,408,843
Class A
Weighted-average Units outstanding
Weighted Average General Partnership Units Outstanding				4,193,031
Class B
Weighted-average Units outstanding
Weighted Average General Partnership Units Outstanding				1,408,305
Class D
Weighted-average Units outstanding
Weighted Average General Partnership Units Outstanding				2,506
Class F
Weighted-average Units outstanding
Weighted Average General Partnership Units Outstanding				835,958