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, 2017	$ 751,130,000	$ 3,000	$ 1,061,153,000	$ (317,032,000)	$ 5,348,000	$ 1,658,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	88,636,000	0	0	88,506,000	0	130,000
Net unrealized change in fair value of interest rate swaps - cash flow hedges	1,353,000	0	0	0	1,353,000	0
Common dividends declared - $2.72, $2.94, and $3.08 per share in 2018, 2019, and 2020 respectively	(97,667,000)	0	0	(97,667,000)	0	0
Stock-based compensation, net of forfeitures	6,103,000	0	6,103,000	0	0	0
Issuance of 1,706,474, 2,388,342, and 709,924 shares of common stock, common stock offering, net of expenses in 2018, 2019, and 2020, respectively	157,319,000	1,000	157,318,000	0	0	0
Issuance of 1,844, 1,893, and zero shares of common stock, dividend reinvestment plan in 2018, 2019, and 2020 respectively	164,000	0	164,000	0	0	0
Withheld 23,824, 28,955, and 36,445 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2018, 2019, and 2020 respectively	(2,055,000)	0	(2,055,000)	0	0	0
Purchase of noncontrolling interest in joint venture	(136,000)	0	(136,000)	0	0	0
Contributions from noncontrolling interest	50,000	0	0	0	0	50,000
Distributions to Noncontrolling Interest Holders	(194,000)	0	0	0	0	(194,000)
BALANCE at Dec. 31, 2018	904,703,000	4,000	1,222,547,000	(326,193,000)	6,701,000	1,644,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	123,340,000	0	0	121,662,000	0	1,678,000
Net unrealized change in fair value of interest rate swaps - cash flow hedges	(3,894,000)	0	0	0	(3,894,000)	0
Common dividends declared - $2.72, $2.94, and $3.08 per share in 2018, 2019, and 2020 respectively	(111,771,000)	0	0	(111,771,000)	0	0
Stock-based compensation, net of forfeitures	9,374,000	0	9,374,000	0	0	0
Issuance of 1,706,474, 2,388,342, and 709,924 shares of common stock, common stock offering, net of expenses in 2018, 2019, and 2020, respectively	284,710,000	0	284,710,000	0	0	0
Issuance of 1,844, 1,893, and zero shares of common stock, dividend reinvestment plan in 2018, 2019, and 2020 respectively	212,000	0	212,000	0	0	0
Withheld 23,824, 28,955, and 36,445 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2018, 2019, and 2020 respectively	(2,788,000)	0	(2,788,000)	0	0	0
Contributions from noncontrolling interest	821,000	0	0	0	0	821,000
Distributions to Noncontrolling Interest Holders	(2,378,000)	0	0	0	0	(2,378,000)
BALANCE at Dec. 31, 2019	1,202,329,000	4,000	1,514,055,000	(316,302,000)	2,807,000	1,765,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	108,391,000	0	0	108,363,000	0	28,000
Net unrealized change in fair value of interest rate swaps - cash flow hedges	(13,559,000)	0	0	0	(13,559,000)	0
Common dividends declared - $2.72, $2.94, and $3.08 per share in 2018, 2019, and 2020 respectively	(121,728,000)	0	0	(121,728,000)	0	0
Stock-based compensation, net of forfeitures	8,502,000	0	8,502,000	0	0	0
Issuance of 1,706,474, 2,388,342, and 709,924 shares of common stock, common stock offering, net of expenses in 2018, 2019, and 2020, respectively	92,663,000	0	92,663,000	0	0	0
Withheld 23,824, 28,955, and 36,445 shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock in 2018, 2019, and 2020 respectively	(4,939,000)	0	(4,939,000)	0	0	0
Contributions from noncontrolling interest	20,000	0	0	0	0	20,000
Distributions to Noncontrolling Interest Holders	(115,000)	0	0	0	0	(115,000)
Sale of noncontrolling interest in joint venture	(1,046,000)	0	(228,000)	0	0	(818,000)
BALANCE at Dec. 31, 2020	$ 1,270,518,000	$ 4,000	$ 1,610,053,000	$ (329,667,000)	$ (10,752,000)	$ 880,000