Stock-based Compensation (Summary of Unrecognized Compensation Expense) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 42,587
Weighted-Average Remaining Contractual Term	1 year 10 months 24 days
OP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 36,390
Weighted-Average Remaining Contractual Term	2 years
AO LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 2,029
Weighted-Average Remaining Contractual Term	1 year 6 months
OPPs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 1,783
Weighted-Average Remaining Contractual Term	1 year 7 months 6 days
Vornado restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 833
Weighted-Average Remaining Contractual Term	1 year 8 months 12 days
Vornado stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 832
Weighted-Average Remaining Contractual Term	1 year 8 months 12 days
Performance Conditioned AO LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 720
Weighted-Average Remaining Contractual Term	1 year 7 months 6 days