Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income (loss)	$ 81,625	$ (24,783)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	77,259	89,295
Amortization of deferred loan costs and debt premiums	2,167	2,619
(Accretion) and amortization of above and below market lease intangibles, net	(5,576)	(12,460)
Stock-based compensation, net of capitalization	2,420	3,320
Equity in income of investments in real estate partnerships	(11,666)	(11,418)
Gain on sale of real estate, net of tax	(11,698)	(38,005)
Provision for impairment of real estate, net of tax		784	$ (17,500)
Goodwill impairment		132,128
Distribution of earnings from investments in real estate partnerships	16,491	16,440
Settlement of derivative instruments	(2,472)
Deferred compensation expense	1,139	(4,328)
Realized and unrealized (gain) loss on investments	(1,354)	4,923
Changes in assets and liabilities:
Tenant and other receivables	15,760	18,569
Deferred leasing costs	(1,907)	(1,352)
Other assets	(9,801)	(12,201)
Accounts payable and other liabilities	(14,716)	(27,498)
Tenants’ security, escrow deposits and prepaid rent	1,691	(10,355)
Net cash provided by operating activities	139,362	125,678
Cash flows from investing activities:
Acquisition of operating real estate		(16,867)
Advance deposits refunded on acquisition of operating real estate	500	100
Real estate development and capital improvements	(31,378)	(56,309)
Proceeds from sale of real estate investments	53,859	103,522
Issuance of notes receivable	(20)	(167)
Investments in real estate partnerships	(20,223)	(32,972)
Return of capital from investments in real estate partnerships	3,283
Dividends on investment securities	51	84
Acquisition of investment securities	(8,136)	(4,392)
Proceeds from sale of investment securities	8,834	4,448
Net cash provided by (used in) investing activities	6,770	(2,553)
Cash flows from financing activities:
Net proceeds from common stock issuance		125,773
Repurchase of common shares in conjunction with equity award plans	(3,996)	(5,298)
Proceeds from sale of treasury stock	96	49
Distributions to limited partners in consolidated partnerships, net	(785)	(1,064)
Distributions to exchangeable operating partnership unit holders	(453)	(455)
Dividends paid to common stockholders	(100,580)	(99,409)
Proceeds from unsecured credit facilities		610,000
Repayment of unsecured credit facilities	(265,000)	(125,000)
Repayment of notes payable	(3,962)	(3,891)
Scheduled principal payments	(3,114)	(2,547)
Payment of loan costs	(7,468)
Net cash (used in) provided by financing activities	(385,262)	498,158
Net (decrease) increase in cash and cash equivalents and restricted cash	(239,130)	621,283
Cash and cash equivalents and restricted cash at beginning of the period	378,450	115,562	115,562
Cash and cash equivalents and restricted cash at end of the period	139,320	736,845	378,450
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $849 and $1,175 in 2021 and 2020, respectively)	44,276	47,912
Cash (refunded) paid for income taxes, net	(101)	317
Supplemental disclosure of non-cash transactions:
Acquisition of real estate previously held within investments in real estate partnerships		5,986
Mortgage loan assumed with the acquisition of real estate		16,359
Issuance of exchangeable operating partnership units		1,275
Change in accrued capital expenditures	874	4,942
Common stock issued under dividend reinvestment plan	376	379
Stock-based compensation capitalized	196	554
Common stock and exchangeable operating partnership dividends declared but not paid	101,500
Common stock issued for dividend reinvestment in trust	274	265
Contribution of stock awards into trust	571	862
Distribution of stock held in trust	415	390
Change in fair value of securities	361	577
Partnership Interest [Member]
Cash flows from operating activities:
Net income (loss)	81,625	(24,783)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	77,259	89,295
Amortization of deferred loan costs and debt premiums	2,167	2,619
(Accretion) and amortization of above and below market lease intangibles, net	(5,576)	(12,460)
Stock-based compensation, net of capitalization	2,420	3,320
Equity in income of investments in real estate partnerships	(11,666)	(11,418)
Gain on sale of real estate, net of tax	(11,698)	(38,005)
Provision for impairment of real estate, net of tax		784
Goodwill impairment		132,128
Distribution of earnings from investments in real estate partnerships	16,491	16,440
Settlement of derivative instruments	(2,472)
Deferred compensation expense	1,139	(4,328)
Realized and unrealized (gain) loss on investments	(1,354)	4,923
Changes in assets and liabilities:
Tenant and other receivables	15,760	18,569
Deferred leasing costs	(1,907)	(1,352)
Other assets	(9,801)	(12,201)
Accounts payable and other liabilities	(14,716)	(27,498)
Tenants’ security, escrow deposits and prepaid rent	1,691	(10,355)
Net cash provided by operating activities	139,362	125,678
Cash flows from investing activities:
Acquisition of operating real estate		(16,867)
Advance deposits refunded on acquisition of operating real estate	500	100
Real estate development and capital improvements	(31,378)	(56,309)
Proceeds from sale of real estate investments	53,859	103,522
Issuance of notes receivable	(20)	(167)
Investments in real estate partnerships	(20,223)	(32,972)
Return of capital from investments in real estate partnerships	3,283
Dividends on investment securities	51	84
Acquisition of investment securities	(8,136)	(4,392)
Proceeds from sale of investment securities	8,834	4,448
Net cash provided by (used in) investing activities	6,770	(2,553)
Cash flows from financing activities:
Net proceeds from common stock issuance		125,773
Repurchase of common shares in conjunction with equity award plans	(3,996)	(5,298)
Proceeds from sale of treasury stock	96	49
Distributions to limited partners in consolidated partnerships, net	(785)	(1,064)
Dividends paid to common stockholders	(101,033)	(99,864)
Proceeds from unsecured credit facilities		610,000
Repayment of unsecured credit facilities	(265,000)	(125,000)
Repayment of notes payable	(3,962)	(3,891)
Scheduled principal payments	(3,114)	(2,547)
Payment of loan costs	(7,468)
Net cash (used in) provided by financing activities	(385,262)	498,158
Net (decrease) increase in cash and cash equivalents and restricted cash	(239,130)	621,283
Cash and cash equivalents and restricted cash at beginning of the period	378,450	115,562	115,562
Cash and cash equivalents and restricted cash at end of the period	139,320	736,845	$ 378,450
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $849 and $1,175 in 2021 and 2020, respectively)	44,276	47,912
Cash (refunded) paid for income taxes, net	(101)	317
Supplemental disclosure of non-cash transactions:
Acquisition of real estate previously held within investments in real estate partnerships		5,986
Mortgage loan assumed with the acquisition of real estate		16,359
Issuance of exchangeable operating partnership units		1,275
Change in accrued capital expenditures	874	4,942
Common stock issued under dividend reinvestment plan	376	379
Stock-based compensation capitalized	196	554
Common stock and exchangeable operating partnership dividends declared but not paid	101,500
Common stock issued for dividend reinvestment in trust	274	265
Contribution of stock awards into trust	571	862
Distribution of stock held in trust	415	390
Change in fair value of securities	$ 361	$ 577