CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - Unaudited (USD $)	Total	Common Stock	Additional Paid-in Capital	Distributions In Excess Of Earnings	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest in Joint Ventures
BALANCE at Dec. 31, 2011	$ 405,609,000	$ 3,000	$ 619,386,000	$ (216,560,000)	$ 0	$ 2,780,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,502,000	0	0	20,146,000	0	356,000
Common dividends declared - $1.57 per share	(45,202,000)	0	0	(45,202,000)	0	0
Stock-based compensation, net of forfeitures	3,571,000	0	3,571,000	0	0	0
Issuance of 1,511,398 shares of common stock, common stock offering, net of expenses	74,903,000	0	74,903,000	0	0	0
Issuance of 4,500 shares of common stock, options exercised	108,000	0	108,000	0	0	0
Issuance of 2,982 shares of common stock, dividend reinvestment plan	155,000	0	155,000	0	0	0
Withheld 17,927 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock	(812,000)	0	(812,000)	0	0	0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period	(605,000)	0	0	0	(605,000)	0
Distributions to noncontrolling interest	(369,000)	0	0	0	0	(369,000)
BALANCE at Sep. 30, 2012	$ 457,860,000	$ 3,000	$ 697,311,000	$ (241,616,000)	$ (605,000)	$ 2,767,000