Fair Value Measurements (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable	$ 3,435,161	$ 3,006,478
Unsecured notes	484,383	708,734
Trading Securities, Change in Unrealized Holding Gain (Loss)	(3,800)	3,300	$ (1,100)
Impairment of Real Estate	54,174	38,437	$ 0
Impairment of Real Estate	50,500
Real Estate Sold [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Real Estate		31,800
Properties Held For Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Real Estate		6,600
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	39,599	33,354
Available-for-sale Securities	10,755	7,933
Interest Rate Derivative Assets, at Fair Value	2,987	17,482
Total	53,341	58,769
Interest Rate Cash Flow Hedge Liability at Fair Value	(1,515)	(5,491)
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating properties	71,131	42,760
Impairment of Real Estate	50,553	6,579
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes Payable, Fair Value	3,688,604	2,961,769
Fair Value, Inputs, Level 2 [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	0	0
Available-for-sale Securities	10,755	7,933
Interest Rate Derivative Assets, at Fair Value	2,987	17,482
Total	13,742	25,415
Interest Rate Cash Flow Hedge Liability at Fair Value	(1,515)	(5,491)
Impairment of Real Estate	10,200
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	28,131	42,760
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	489,496	710,902
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	39,599	33,354
Available-for-sale Securities	0	0
Interest Rate Derivative Assets, at Fair Value	0	0
Total	39,599	33,354
Interest Rate Cash Flow Hedge Liability at Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating properties	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Real Estate	$ 40,300
Fair Value, Inputs, Level 3 [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment Rate	8.58
Fair Value, Inputs, Level 3 [Member] | Terminal Capitalization Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment Rate	4.75
Fair Value, Inputs, Level 3 [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	$ 0	0
Available-for-sale Securities	0	0
Interest Rate Derivative Assets, at Fair Value	0	0
Total	0	0
Interest Rate Cash Flow Hedge Liability at Fair Value	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating properties	43,000	$ 0
Alternative Investment	$ 43,000