CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $)	Total	Common Stock	Additional Paid-in Capital	Distributions In Excess Of Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Joint Ventures
BALANCE at Dec. 31, 2010	$ 411,506,000	$ 3,000	$ 591,106,000	$ (182,253,000)	$ 0	$ 2,650,000
Comprehensive income
Net income	22,834,000	0	0	22,359,000	0	475,000
Net unrealized change in fair value of interest rate swaps	0
Common dividends declared - $2.08, $2.10 and $2.14 per share in 2011, 2012 and 2013, respectively	(56,666,000)	0	0	(56,666,000)	0	0
Stock-based compensation, net of forfeitures	2,787,000	0	2,787,000	0	0	0
Issuance of 586,977, 2,179,153 and 890,085 shares of common stock, common stock offering, net of expenses in 2011, 2012 and 2013, respectively	25,181,000	0	25,181,000	0	0	0
Issuance of 9,250, 4,500 and 4,500 shares of common stock, options exercised in 2011, 2012 and 2013, respectively	217,000	0	217,000	0	0	0
Issuance of 5,989, 3,915 and 3,577 shares of common stock, dividend reinvestment plan in 2011, 2012 and 2013, respectively	252,000	0	252,000	0	0	0
Withheld 3,564, 36,195 and 9,412 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2011, 2012 and 2013, respectively	(157,000)	0	(157,000)	0	0	0
Distributions to noncontrolling interest	(345,000)	0	0	0	0	(345,000)
BALANCE at Dec. 31, 2011	405,609,000	3,000	619,386,000	(216,560,000)	0	2,780,000
Comprehensive income
Net income	32,887,000	0	0	32,384,000	0	503,000
Net unrealized change in fair value of interest rate swaps	(392,000)	0	0	0	(392,000)	0
Common dividends declared - $2.08, $2.10 and $2.14 per share in 2011, 2012 and 2013, respectively	(61,073,000)	0	0	(61,073,000)	0	0
Stock-based compensation, net of forfeitures	4,447,000	0	4,447,000	0	0	0
Issuance of 586,977, 2,179,153 and 890,085 shares of common stock, common stock offering, net of expenses in 2011, 2012 and 2013, respectively	109,588,000	0	109,588,000	0	0	0
Issuance of 9,250, 4,500 and 4,500 shares of common stock, options exercised in 2011, 2012 and 2013, respectively	108,000	0	108,000	0	0	0
Issuance of 5,989, 3,915 and 3,577 shares of common stock, dividend reinvestment plan in 2011, 2012 and 2013, respectively	205,000	0	205,000	0	0	0
Withheld 3,564, 36,195 and 9,412 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2011, 2012 and 2013, respectively	(1,784,000)	0	(1,784,000)	0	0	0
Distributions to noncontrolling interest	(537,000)	0	0	0	0	(537,000)
Contributions from noncontrolling interest	2,118,000	0	0	0	0	2,118,000
BALANCE at Dec. 31, 2012	491,176,000	3,000	731,950,000	(245,249,000)	(392,000)	4,864,000
Comprehensive income
Net income	33,225,000	0	0	32,615,000	0	610,000
Net unrealized change in fair value of interest rate swaps	2,021,000	0	0	0	2,021,000	0
Common dividends declared - $2.08, $2.10 and $2.14 per share in 2011, 2012 and 2013, respectively	(65,535,000)	0	0	(65,535,000)	0	0
Stock-based compensation, net of forfeitures	5,540,000	0	5,540,000	0	0	0
Issuance of 586,977, 2,179,153 and 890,085 shares of common stock, common stock offering, net of expenses in 2011, 2012 and 2013, respectively	53,247,000	0	53,247,000	0	0	0
Issuance of 9,250, 4,500 and 4,500 shares of common stock, options exercised in 2011, 2012 and 2013, respectively	120,000	0	120,000	0	0	0
Issuance of 5,989, 3,915 and 3,577 shares of common stock, dividend reinvestment plan in 2011, 2012 and 2013, respectively	206,000	0	206,000	0	0	0
Withheld 3,564, 36,195 and 9,412 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2011, 2012 and 2013, respectively	(528,000)	0	(528,000)	0	0	0
Distributions to noncontrolling interest	(767,000)	0	0	0	0	(767,000)
BALANCE at Dec. 31, 2013	$ 518,705,000	$ 3,000	$ 790,535,000	$ (278,169,000)	$ 1,629,000	$ 4,707,000