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, 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 - $2.22, $2.34 and $2.44 per share in 2014, 2015 and 2016, 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 1,246,400, 106,751 and 875,052 shares of common stock, common stock offering, net of expenses in 2014, 2015 and 2016, respectively	78,868,000	0	78,868,000	0	0	0
Issuance of 3,626, 4,536 and 3,326 shares of common stock, dividend reinvestment plan in 2014, 2015 and 2016, respectively	227,000	0	227,000	0	0	0
Withheld 31,673, 32,409 and 57,316 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2014, 2015 and 2016, 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 - $2.22, $2.34 and $2.44 per share in 2014, 2015 and 2016, 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 1,246,400, 106,751 and 875,052 shares of common stock, common stock offering, net of expenses in 2014, 2015 and 2016, respectively	6,233,000	0	6,233,000	0	0	0
Issuance of 3,626, 4,536 and 3,326 shares of common stock, dividend reinvestment plan in 2014, 2015 and 2016, respectively	257,000	0	257,000	0	0	0
Withheld 31,673, 32,409 and 57,316 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2014, 2015 and 2016, 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
Comprehensive income
Net income	96,094,000	0	0	95,509,000	0	585,000
Net unrealized change in fair value of interest rate swaps	5,451,000	0	0	0	5,451,000	0
Common dividends declared - $2.22, $2.34 and $2.44 per share in 2014, 2015 and 2016, respectively	(80,272,000)	0	0	(80,272,000)	0	0
Stock-based compensation, net of forfeitures	5,831,000	0	5,831,000	0	0	0
Issuance of 1,246,400, 106,751 and 875,052 shares of common stock, common stock offering, net of expenses in 2014, 2015 and 2016, respectively	59,283,000	0	59,283,000	0	0	0
Issuance of 3,626, 4,536 and 3,326 shares of common stock, dividend reinvestment plan in 2014, 2015 and 2016, respectively	228,000	0	228,000	0	0	0
Withheld 31,673, 32,409 and 57,316 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2014, 2015 and 2016, respectively	(3,231,000)	0	(3,231,000)	0	0	0
Distributions to noncontrolling interest	(719,000)	0	0	0	0	(719,000)
BALANCE at Dec. 31, 2016	$ 641,866,000	$ 3,000	$ 949,318,000	$ (313,655,000)	$ 1,995,000	$ 4,205,000