Fair Value (Assets Measured on a Non-recurring Basis) (Details) - Fair Value, Measurements, Nonrecurring $ in Thousands	Jun. 30, 2021 USD ($)	Dec. 31, 2020	Jun. 30, 2020 USD ($)	Mar. 31, 2020
Measurement Input, Cap Rate | Discounted cash flow analysis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value capitalization rate		0.100		0.10
Century Park | Strategic Developments Segment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	$ 32,000
Century Park | Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) | Strategic Developments Segment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	0
Century Park | Fair Value Measurements Using Significant Other Observable Inputs (Level 2) | Strategic Developments Segment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	0
Century Park | Fair Value Measurements Using Significant Unobservable Inputs (Level 3) | Strategic Developments Segment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	$ 32,000
Outlet Collection At Riverwalk | Operating Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis			$ 46,794
Outlet Collection At Riverwalk | Fair Value Measurements Using Quoted Prices in Active Markets for Identical Assets (Level 1) | Operating Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis			0
Outlet Collection At Riverwalk | Fair Value Measurements Using Significant Other Observable Inputs (Level 2) | Operating Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis			0
Outlet Collection At Riverwalk | Fair Value Measurements Using Significant Unobservable Inputs (Level 3) | Operating Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis			$ 46,794