Company Earning Per Share - Schedule of Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 18,934	$ 22,322	$ 21,170	$ 21,865	$ 3,920	$ 8,828	$ 9,834	$ 3,013	$ 84,291	$ 25,595	$ (6,991)
Noncontrolling interests-consolidated real estate entities									(135)	(67)	(20)
Noncontrolling interests-Operating Partnership									(217)	(62)	51
Dividends to preferred shareholders	(922)	(922)	(922)	(922)	(922)	(922)	(922)	(1,689)	(3,688)	(4,455)	(7,503)
Preferred stock redemption costs								(1,757)		(1,757)	(44)
Unvested restricted stock (allocation of earnings)									(186)	(59)	65
Net income (loss) available to common unitholders									$ 80,065	$ 19,195	$ (14,442)
Weighted average shares outstanding-basic									53,821	50,420	48,483
Dilutive shares from stock options									310	388
Weighted average shares outstanding-diluted									54,131	50,808	48,483
Basic	$ 0.33	$ 0.39	$ 0.37	$ 0.39	$ 0.06	$ 0.15	$ 0.18	$ (0.01)	$ 1.49	$ 0.38	$ (0.30)
Diluted	$ 0.33	$ 0.39	$ 0.37	$ 0.39	$ 0.06	$ 0.15	$ 0.17	$ (0.01)	$ 1.48	$ 0.38	$ (0.30)