CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES
Net income	$ 157,638,000	$ 108,391,000	$ 123,340,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	127,099,000	116,359,000	104,724,000
Stock-based compensation expense	7,511,000	6,579,000	6,838,000
Gain on sales of real estate investments	(38,859,000)	(13,145,000)	(41,068,000)
Gain on casualties and involuntary conversion on real estate assets	0	(161,000)	(180,000)
Changes in operating assets and liabilities:
Accrued income and other assets	(11,572,000)	(4,615,000)	(5,558,000)
Accounts payable, accrued expenses and prepaid rent	13,298,000	(18,851,000)	6,514,000
Other	1,377,000	1,728,000	1,302,000
NET CASH PROVIDED BY OPERATING ACTIVITIES	256,492,000	196,285,000	195,912,000
INVESTING ACTIVITIES
Development and value-add properties	(418,855,000)	(195,446,000)	(318,288,000)
Purchases of real estate	(108,149,000)	(49,199,000)	(142,712,000)
Real estate improvements	(36,665,000)	(33,131,000)	(37,775,000)
Net proceeds from sales of real estate investments and non-operating real estate	44,260,000	21,565,000	66,737,000
Leasing commissions	(33,301,000)	(17,516,000)	(19,194,000)
Proceeds from casualties and involuntary conversion on real estate assets	0	242,000	723,000
Repayments on mortgage loans receivable	0	1,679,000	915,000
Changes in accrued development costs	21,678,000	(5,339,000)	(3,644,000)
Changes in other assets and other liabilities	1,769,000	(11,111,000)	9,901,000
NET CASH USED IN INVESTING ACTIVITIES	(529,263,000)	(288,256,000)	(443,337,000)
FINANCING ACTIVITIES
Proceeds from unsecured bank credit facilities	625,520,000	625,387,000	932,658,000
Repayments on unsecured bank credit facilities	(541,310,000)	(613,097,000)	(1,015,678,000)
Proceeds from unsecured debt	175,000,000	275,000,000	290,000,000
Repayments on unsecured debt	(40,000,000)	(105,000,000)	(75,000,000)
Repayments on secured debt	(76,920,000)	(54,306,000)	(55,593,000)
Debt issuance costs	(2,678,000)	(1,090,000)	(893,000)
Distributions paid to stockholders (not including dividends accrued)	(131,759,000)	(119,765,000)	(108,795,000)
Proceeds from common stock offerings	273,097,000	90,721,000	284,710,000
Proceeds from dividend reinvestment plan	0	0	212,000
Other	(3,807,000)	(6,082,000)	(4,346,000)
NET CASH PROVIDED BY FINANCING ACTIVITIES	277,143,000	91,768,000	247,275,000
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	4,372,000	(203,000)	(150,000)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	21,000	224,000	374,000
CASH AND CASH EQUIVALENTS AT END OF YEAR	4,393,000	21,000	224,000
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid for interest, net of amount capitalized of $9,028, $9,651, and $8,453 for 2021, 2020, and 2019, respectively	31,658,000	32,362,000	30,839,000
Cash paid for interest, net of amount capitalized	9,028,000	9,651,000	8,453,000
Cash paid for operating lease liabilities	1,707,000	1,476,000	1,314,000
NON-CASH OPERATING ACTIVITY
Operating lease liabilities arising from obtaining right of use assets	$ 13,056,000	$ 495,000	$ 15,435,000