Fair Value Disclosures (Measurements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities, unrealized gain			$ (300)			$ 100
Impairment of real estate	$ 5,962	$ 6,186	10,560	$ 9,298
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Terminal capitalization rates	8.00%
Minimum | Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	8.00%
30th Street Plaza
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value	$ 6,100		6,100
Chamberlain Plaza
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value	2,200		2,200
Spring Mall
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value	4,900		4,900
Brice Park
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value						9,700
Mohawk Acres Plaza
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value						9,100
Lincoln Plaza
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value						3,400
Lakes Crossing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value						1,300
Fair Value, Measurements, Recurring | Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	20,765		20,765			18,054
Fair Value, Measurements, Recurring | Interest Rate Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset						3,795
Derivative liability	(34,367)		(34,367)			(13,449)
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	4,683		4,683			1,459
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest Rate Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset						0
Derivative liability	0		0			0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	16,082		16,082			16,595
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest Rate Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset						3,795
Derivative liability	34,367		34,367			(13,449)
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Marketable Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0		0			0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Interest Rate Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset						0
Derivative liability	0		0			0
Fair Value, Measurements, Nonrecurring | Properties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	13,155		13,155			23,533
Impairment of real estate			10,546		$ 7,983
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Properties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0		0			0
Fair Value, Measurements, Nonrecurring | Significant Other Observable Inputs (Level 2) | Properties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0		0			0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | Properties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	$ 13,155		$ 13,155			$ 23,533