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, 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 - $2.14, $2.22 and $2.34 per share in 2013, 2014 and 2015, 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 890,085, 1,246,400 and 106,751 shares of common stock, common stock offering, net of expenses in 2013, 2014 and 2015, respectively	53,247,000	0	53,247,000	0	0	0
Issuance of 4,500 shares of common stock, options exercised in 2013	120,000	0	120,000	0	0	0
Issuance of 3,577, 3,626 and 4,536 shares of common stock, dividend reinvestment plan in 2013, 2014 and 2015, respectively	206,000	0	206,000	0	0	0
Withheld 9,412, 31,673 and 32,409 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2013, 2014 and 2015, 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
Comprehensive income
Net income	48,473,000	0	0	47,941,000	0	532,000
Net unrealized change in fair value of interest rate swaps	(3,986,000)	0	0	0	(3,986,000)	0
Common dividends declared - $2.14, $2.22 and $2.34 per share in 2013, 2014 and 2015, respectively	(70,624,000)	0	0	(70,624,000)	0	0
Stock-based compensation, net of forfeitures	6,567,000	0	6,567,000	0	0	0
Issuance of 890,085, 1,246,400 and 106,751 shares of common stock, common stock offering, net of expenses in 2013, 2014 and 2015, respectively	78,868,000	0	78,868,000	0	0	0
Issuance of 3,577, 3,626 and 4,536 shares of common stock, dividend reinvestment plan in 2013, 2014 and 2015, respectively	227,000	0	227,000	0	0	0
Withheld 9,412, 31,673 and 32,409 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2013, 2014 and 2015, respectively	(1,862,000)	0	(1,862,000)	0	0	0
Distributions to noncontrolling interest	(753,000)	0	0	0	0	(753,000)
BALANCE at Dec. 31, 2014	575,615,000	3,000	874,335,000	(300,852,000)	(2,357,000)	4,486,000
Comprehensive income
Net income	48,399,000	0	0	47,866,000	0	533,000
Net unrealized change in fair value of interest rate swaps	(1,099,000)	0	0	0	(1,099,000)	0
Common dividends declared - $2.14, $2.22 and $2.34 per share in 2013, 2014 and 2015, respectively	(75,906,000)	0	0	(75,906,000)	0	0
Stock-based compensation, net of forfeitures	8,423,000	0	(8,423,000)	0	0	0
Issuance of 890,085, 1,246,400 and 106,751 shares of common stock, common stock offering, net of expenses in 2013, 2014 and 2015, respectively	6,233,000	0	6,233,000	0	0	0
Issuance of 3,577, 3,626 and 4,536 shares of common stock, dividend reinvestment plan in 2013, 2014 and 2015, respectively	257,000	0	257,000	0	0	0
Withheld 9,412, 31,673 and 32,409 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2013, 2014 and 2015, respectively	(2,041,000)	0	2,041,000	0	0	0
Distributions to noncontrolling interest	(680,000)	0	0	0	0	(680,000)
BALANCE at Dec. 31, 2015	$ 559,201,000	$ 3,000	$ 887,207,000	$ (328,892,000)	$ (3,456,000)	$ 4,339,000