Fair Value (Assets Measured on a Non-recurring Basis) (Details) - Fair Value, Measurements, Nonrecurring $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Measurement Input, Cap Rate | Discounted cash flow analysis | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment property, measurement input	0.065
Real estate investment property, discount rate	9.50%
Real estate investment property, restaurant multiple	8.3
Measurement Input, Cap Rate | Discounted cash flow analysis | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate investment property, measurement input	0.0675
Real estate investment property, discount rate	13.30%
Real estate investment property, restaurant multiple	11.8
Seaport Net investment in real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	$ 321,180
Seaport Net investment in real estate | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	0
Seaport Net investment in real estate | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	0
Seaport Net investment in real estate | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	321,180
Seaport Investments in unconsolidated ventures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	40,225
Seaport Investments in unconsolidated ventures | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	0
Seaport Investments in unconsolidated ventures | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	0
Seaport Investments in unconsolidated ventures | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value on non-recurring basis	$ 40,225