Schedule III—Real Estate And Accumulated Depreciation - Real Estate And Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate And Accumulated Depreciation
Encumbrances	$ 750,000
Initial Cost
Land	1,700,062
Building & Improvements	4,604,432
Cost Capitalized Subsequent To Acquisition
Land	4,080
Building & Improvements	720,881
Gross Amount at Which Carried at Close of Period
Land	1,704,142
Building & Improvements	5,325,313
Total	7,029,455	$ 7,508,870	$ 7,428,243	$ 7,203,216
Accumulated Depreciation	1,492,603	$ 1,437,222	$ 1,267,598	$ 1,123,412
810 Seventh Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	114,077
Building & Improvements	476,386
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	71,735
Gross Amount at Which Carried at Close of Period
Land	114,077
Building & Improvements	548,121
Total	662,198
Accumulated Depreciation	162,606
461 Fifth Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	62,695
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	16,185
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	78,880
Total	78,880
Accumulated Depreciation	28,378
750 Third Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	51,093
Building & Improvements	205,972
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	42,543
Gross Amount at Which Carried at Close of Period
Land	51,093
Building & Improvements	248,515
Total	299,608
Accumulated Depreciation	93,469
919 Third Avenue
Real Estate And Accumulated Depreciation
Encumbrances	500,000
Initial Cost
Land	223,529
Building & Improvements	1,033,198
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	65,089
Gross Amount at Which Carried at Close of Period
Land	223,529
Building & Improvements	1,098,287
Total	1,321,816
Accumulated Depreciation	$ 303,424
Interest in property (as a percent)	51.00%
555 W. 57th Street
Real Estate And Accumulated Depreciation
Encumbrances	$ 0
Initial Cost
Land	18,846
Building & Improvements	78,704
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	61,424
Gross Amount at Which Carried at Close of Period
Land	18,846
Building & Improvements	140,128
Total	158,974
Accumulated Depreciation	64,281
1185 Avenue of the Americas
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	728,213
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	47,793
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	776,006
Total	776,006
Accumulated Depreciation	242,681
1350 Avenue of the Americas
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	91,038
Building & Improvements	380,744
Cost Capitalized Subsequent To Acquisition
Land	(97)
Building & Improvements	41,911
Gross Amount at Which Carried at Close of Period
Land	90,941
Building & Improvements	422,655
Total	513,596
Accumulated Depreciation	124,638
100 Summit Lake Drive
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	10,526
Building & Improvements	43,109
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	11,215
Gross Amount at Which Carried at Close of Period
Land	10,526
Building & Improvements	54,324
Total	64,850
Accumulated Depreciation	16,963
200 Summit Lake Drive
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	11,183
Building & Improvements	47,906
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	11,177
Gross Amount at Which Carried at Close of Period
Land	11,183
Building & Improvements	59,083
Total	70,266
Accumulated Depreciation	18,818
500 Summit Lake Drive
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	9,777
Building & Improvements	39,048
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,358
Gross Amount at Which Carried at Close of Period
Land	9,777
Building & Improvements	45,406
Total	55,183
Accumulated Depreciation	13,074
360 Hamilton Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	29,497
Building & Improvements	118,250
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	15,392
Gross Amount at Which Carried at Close of Period
Land	29,497
Building & Improvements	133,642
Total	163,139
Accumulated Depreciation	39,811
1010 Washington Boulevard
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	7,747
Building & Improvements	30,423
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	7,378
Gross Amount at Which Carried at Close of Period
Land	7,747
Building & Improvements	37,801
Total	45,548
Accumulated Depreciation	11,044
1055 Washington Boulevard
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	13,516
Building & Improvements	53,228
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	8,390
Gross Amount at Which Carried at Close of Period
Land	13,516
Building & Improvements	61,618
Total	75,134
Accumulated Depreciation	18,075
400 Summit Lake Drive
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	38,889
Building & Improvements	1
Cost Capitalized Subsequent To Acquisition
Land	285
Building & Improvements	3
Gross Amount at Which Carried at Close of Period
Land	39,174
Building & Improvements	4
Total	39,178
Accumulated Depreciation	0
609 Fifth Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	36,677
Building & Improvements	145,954
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	10,435
Gross Amount at Which Carried at Close of Period
Land	36,677
Building & Improvements	156,389
Total	193,066
Accumulated Depreciation	46,059
110 East 42nd Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	34,000
Building & Improvements	46,411
Cost Capitalized Subsequent To Acquisition
Land	(138)
Building & Improvements	23,984
Gross Amount at Which Carried at Close of Period
Land	33,862
Building & Improvements	70,395
Total	104,257
Accumulated Depreciation	17,244
304 Park Avenue South
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	54,189
Building & Improvements	75,619
Cost Capitalized Subsequent To Acquisition
Land	300
Building & Improvements	14,550
Gross Amount at Which Carried at Close of Period
Land	54,489
Building & Improvements	90,169
Total	144,658
Accumulated Depreciation	16,445
635 Sixth Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	24,180
Building & Improvements	37,158
Cost Capitalized Subsequent To Acquisition
Land	163
Building & Improvements	51,805
Gross Amount at Which Carried at Close of Period
Land	24,343
Building & Improvements	88,963
Total	113,306
Accumulated Depreciation	7,854
641 Sixth Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	45,668
Building & Improvements	67,316
Cost Capitalized Subsequent To Acquisition
Land	308
Building & Improvements	6,029
Gross Amount at Which Carried at Close of Period
Land	45,976
Building & Improvements	73,345
Total	119,321
Accumulated Depreciation	12,097
315 West 33rd Street
Real Estate And Accumulated Depreciation
Encumbrances	250,000
Initial Cost
Land	195,834
Building & Improvements	164,429
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	11,583
Gross Amount at Which Carried at Close of Period
Land	195,834
Building & Improvements	176,012
Total	371,846
Accumulated Depreciation	19,966
Williamsburg
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	3,677
Building & Improvements	14,708
Cost Capitalized Subsequent To Acquisition
Land	2,523
Building & Improvements	(4,550)
Gross Amount at Which Carried at Close of Period
Land	6,200
Building & Improvements	10,158
Total	16,358
Accumulated Depreciation	1,865
115 Spring Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	11,078
Building & Improvements	44,799
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	1,759
Gross Amount at Which Carried at Close of Period
Land	11,078
Building & Improvements	46,558
Total	57,636
Accumulated Depreciation	4,083
635 Madison Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	205,632
Building & Improvements	15,805
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	205,632
Building & Improvements	15,805
Total	221,437
Accumulated Depreciation	1,306
125 Park Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	120,900
Building & Improvements	189,714
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	74,660
Gross Amount at Which Carried at Close of Period
Land	120,900
Building & Improvements	264,374
Total	385,274
Accumulated Depreciation	65,529
625 Madison Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	246,673
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	43,175
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	289,848
Total	289,848
Accumulated Depreciation	107,791
711 Third Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	19,844
Building & Improvements	42,499
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	66,553
Gross Amount at Which Carried at Close of Period
Land	19,844
Building & Improvements	109,052
Total	128,896
Accumulated Depreciation	$ 39,396
Interest in property (as a percent)	50.00%
752 Madison Avenue
Real Estate And Accumulated Depreciation
Encumbrances	$ 0
Initial Cost
Land	282,415
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	1,871
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	284,286
Building & Improvements	0
Total	284,286
Accumulated Depreciation	12
110 Greene Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	45,120
Building & Improvements	215,470
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	9,611
Gross Amount at Which Carried at Close of Period
Land	45,120
Building & Improvements	225,081
Total	270,201
Accumulated Depreciation	$ 15,693
Interest in property (as a percent)	90.00%
Other
Real Estate And Accumulated Depreciation
Encumbrances	$ 0
Initial Cost
Land	1,130
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	(1,135)
Building & Improvements	4,694
Gross Amount at Which Carried at Close of Period
Land	(5)
Building & Improvements	4,694
Total	4,689
Accumulated Depreciation	$ 1

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