Fair Value Measurements - Financial Instruments at Fair Value (Details) - Mortgages - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value | Samsonite | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	$ 22,103	$ 22,440
Fair Value | Highway 94 loan | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	15,101	15,601
Fair Value | AIG Loan II | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	122,258	0
Fair Value | BOA/KeyBank Loan | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	264,101	0
Fair Value | AIG Loan | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	101,663	108,032
Carrying Value | Samsonite
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	21,154	22,085
Carrying Value | Highway 94 loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	15,610	16,497
Carrying Value | AIG Loan II
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	126,970	0
Carrying Value | BOA/KeyBank Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	250,000	0
Carrying Value | AIG Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	$ 105,762	$ 107,562