Fair Value Disclosures (Measurements) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jun. 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	$ 4,598	$ 3,112
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%
Spring Mall
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment, fair value	$ 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	17,550			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	(33,532)			(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	1,054			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
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	16,496			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	33,532			(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
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
Fair Value, Measurements, Nonrecurring | Properties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	4,889			23,533
Impairment of real estate	4,584		$ 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
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
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	$ 4,889			$ 23,533