Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of unrealized gain (loss) on investment in debt and equity securities.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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The charge against earnings in the period to reduce the carrying amount of real property to fair value.

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Fair value as of the balance sheet date of all interest rate derivative liabilities designated as cash flow hedging instruments.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Fair value portion of notes payable.

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Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable	$ 3,650,307		$ 3,650,307		$ 3,658,405
Unsecured credit facilities					264,679
Trading Securities, Change in Unrealized Holding Gain (Loss)	1,400	$ (4,300)	1,800	$ (1,100)
Impairment of Real Estate	(135)	(230)	(135)	(1,014)
Provision for impairment of real estate	135	$ 230	135	$ 1,014
Real Estate Partnership
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Real Estate			(9,700)
Provision for impairment of real estate			9,700
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	47,734		47,734		44,986
Available-for-sale Securities	15,922		15,922		15,706
Total	63,656		63,656		60,692
Interest Rate Cash Flow Hedge Liability at Fair Value	(4,729)		(4,729)		(9,291)
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating properties	27,657		27,657		25,000
Impairment of Real Estate			(9,741)		(17,532)
Provision for impairment of real estate			9,741		17,532
Fair Value Inputs Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable, Fair Value	4,066,737		4,066,737		4,102,382
Fair Value Inputs Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	15,922		15,922		15,706
Total	15,922		15,922		15,706
Interest Rate Cash Flow Hedge Liability at Fair Value	(4,729)		(4,729)		(9,291)
Fair Value Inputs Level 2 [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating properties	27,657		27,657		25,000
Fair Value Inputs Level 2 [Member] \| Unsecured Credit Facilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unsecured credit facilities, Fair Value					265,226
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	47,734		47,734		44,986
Total	$ 47,734		$ 47,734		$ 44,986