CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES
Net income	$ 123,340,000	$ 88,636,000	$ 83,589,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	104,724,000	91,704,000	83,874,000
Stock-based compensation expense	6,838,000	5,283,000	5,521,000
Net gain on sales of real estate investments and non-operating real estate	(41,151,000)	(14,359,000)	(22,148,000)
Gain on casualties and involuntary conversion on real estate assets	(180,000)	(1,245,000)	0
Changes in operating assets and liabilities:
Accrued income and other assets	(5,558,000)	(4,091,000)	(5,034,000)
Accounts payable, accrued expenses and prepaid rent	6,514,000	(2,682,000)	8,333,000
Other	1,385,000	1,485,000	879,000
NET CASH PROVIDED BY OPERATING ACTIVITIES	195,912,000	164,731,000	155,014,000
INVESTING ACTIVITIES
Development and value-add properties	(318,288,000)	(167,667,000)	(124,938,000)
Purchases of real estate	(142,712,000)	(57,152,000)	(55,195,000)
Real estate improvements	(37,775,000)	(37,502,000)	(27,385,000)
Net proceeds from sales of real estate investments and non-operating real estate	66,737,000	24,508,000	42,710,000
Proceeds from casualties and involuntary conversion on real estate assets	723,000	1,635,000	0
Repayments on mortgage loans receivable	915,000	1,987,000	171,000
Changes in accrued development costs	(3,644,000)	5,711,000	(144,000)
Changes in other assets and other liabilities	(9,293,000)	(12,955,000)	(14,645,000)
NET CASH USED IN INVESTING ACTIVITIES	(443,337,000)	(241,435,000)	(179,426,000)
FINANCING ACTIVITIES
Proceeds from unsecured bank credit facilities	932,658,000	448,100,000	391,617,000
Repayments on unsecured bank credit facilities	(1,015,678,000)	(448,709,000)	(387,298,000)
Proceeds from unsecured debt	290,000,000	60,000,000	60,000,000
Repayments on unsecured debt	(75,000,000)	(50,000,000)	0
Repayments on secured debt	(55,593,000)	(11,289,000)	(58,209,000)
Debt issuance costs	(893,000)	(1,922,000)	(380,000)
Distributions paid to stockholders (not including dividends accrued)	(108,795,000)	(71,294,000)	(86,725,000)
Proceeds from common stock offerings	284,710,000	157,319,000	109,207,000
Proceeds from dividend reinvestment plan	212,000	221,000	228,000
Other	(4,346,000)	(5,364,000)	(4,534,000)
NET CASH PROVIDED BY FINANCING ACTIVITIES	247,275,000	77,062,000	23,906,000
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(150,000)	358,000	(506,000)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	374,000	16,000	522,000
CASH AND CASH EQUIVALENTS AT END OF YEAR	224,000	374,000	16,000
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid for interest, net of amount capitalized of $8,453, $6,334, and $5,765 for 2019, 2018 and 2017, respectively	30,839,000	33,458,000	33,634,000
Cash paid for operating lease liability	1,314,000	0	0
NON-CASH OPERATING ACTIVITY
Operating lease liabilities arising from obtaining right of use assets	$ 15,435,000	$ 0	$ 0