Organization and Basis of Presentation - Schedule of Commercial Office Properties (Details) $ in Billions	6 Months Ended
	Jun. 30, 2020 USD ($) ft² building shares
Real estate properties
Number of Properties | building	72
Approximate Square Feet unaudited (sqft) | ft²	29,843,409
Weighted Average Occupancy unaudited (as a percent)	93.20%
Debt and preferred equity investments including investments held by unconsolidated joint ventures | $	$ 1.3
Debt and preferred equity investments and other financing receivables included in other balance sheet items | $	$ 0.1
Number of shares to be received on redemption of one unit of limited partnership interests (shares) | shares	1
Commercial properties
Real estate properties
Number of Properties | building	62
Approximate Square Feet unaudited (sqft) | ft²	27,957,385
Weighted Average Occupancy unaudited (as a percent)	93.40%
Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet unaudited (sqft) | ft²	1,886,024
Weighted Average Occupancy unaudited (as a percent)	90.00%
Managed office properties
Real estate properties
Number of Properties | building	2
Approximate Square Feet unaudited (sqft) | ft²	2,100,000
Consolidated properties
Real estate properties
Number of Properties | building	44
Approximate Square Feet unaudited (sqft) | ft²	15,017,204
Consolidated properties | Commercial properties
Real estate properties
Number of Properties | building	42
Approximate Square Feet unaudited (sqft) | ft²	14,794,954
Consolidated properties | Residential
Real estate properties
Number of Properties | building	2
Approximate Square Feet unaudited (sqft) | ft²	222,250
Unconsolidated properties
Real estate properties
Number of Properties | building	28
Approximate Square Feet unaudited (sqft) | ft²	14,826,205
Unconsolidated properties | Commercial properties
Real estate properties
Number of Properties | building	20
Approximate Square Feet unaudited (sqft) | ft²	13,162,431
Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	8
Approximate Square Feet unaudited (sqft) | ft²	1,663,774
Manhattan
Real estate properties
Number of Properties | building	53
Approximate Square Feet unaudited (sqft) | ft²	26,860,585
Weighted Average Occupancy unaudited (as a percent)	93.70%
Manhattan | Office
Real estate properties
Number of Properties | building	28
Approximate Square Feet unaudited (sqft) | ft²	21,863,374
Weighted Average Occupancy unaudited (as a percent)	93.70%
Manhattan | Retail
Real estate properties
Number of Properties | building	12
Approximate Square Feet unaudited (sqft) | ft²	333,239
Weighted Average Occupancy unaudited (as a percent)	94.00%
Manhattan | Development/Redevelopment
Real estate properties
Number of Properties | building	12
Approximate Square Feet unaudited (sqft) | ft²	4,663,972
Manhattan | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft) | ft²	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Manhattan | Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet unaudited (sqft) | ft²	1,886,024
Weighted Average Occupancy unaudited (as a percent)	90.00%
Manhattan | Consolidated properties
Real estate properties
Number of Properties | building	33
Approximate Square Feet unaudited (sqft) | ft²	13,698,154
Manhattan | Consolidated properties | Office
Real estate properties
Number of Properties | building	18
Approximate Square Feet unaudited (sqft) | ft²	10,647,191
Manhattan | Consolidated properties | Retail
Real estate properties
Number of Properties | building	4
Approximate Square Feet unaudited (sqft) | ft²	44,189
Manhattan | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	11
Approximate Square Feet unaudited (sqft) | ft²	3,006,774
Manhattan | Consolidated properties | Fee Interest
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft) | ft²	0
Manhattan | Consolidated properties | Residential
Real estate properties
Number of Properties | building	2
Approximate Square Feet unaudited (sqft) | ft²	222,250
Manhattan | Unconsolidated properties
Real estate properties
Number of Properties | building	20
Approximate Square Feet unaudited (sqft) | ft²	13,162,431
Manhattan | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	10
Approximate Square Feet unaudited (sqft) | ft²	11,216,183
Manhattan | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	8
Approximate Square Feet unaudited (sqft) | ft²	289,050
Manhattan | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft) | ft²	1,657,198
Manhattan | Unconsolidated properties | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft) | ft²	0
Manhattan | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	8
Approximate Square Feet unaudited (sqft) | ft²	1,663,774
Suburban
Real estate properties
Number of Properties | building	9
Approximate Square Feet unaudited (sqft) | ft²	1,096,800
Weighted Average Occupancy unaudited (as a percent)	86.20%
Suburban | Office
Real estate properties
Number of Properties | building	8
Approximate Square Feet unaudited (sqft) | ft²	1,044,800
Weighted Average Occupancy unaudited (as a percent)	86.30%
Suburban | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft) | ft²	52,000
Weighted Average Occupancy unaudited (as a percent)	100.00%
Suburban | Consolidated properties
Real estate properties
Number of Properties | building	9
Approximate Square Feet unaudited (sqft) | ft²	1,096,800
Suburban | Consolidated properties | Office
Real estate properties
Number of Properties | building	8
Approximate Square Feet unaudited (sqft) | ft²	1,044,800
Suburban | Consolidated properties | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft) | ft²	52,000
Suburban | Unconsolidated properties
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft) | ft²	0
Suburban | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft) | ft²	0
Suburban | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft) | ft²	0