Schedule III - Real Estate And Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Real Estate And Accumulated Depreciation
Encumbrances	$ 500,000
Initial Cost
Land	1,869,857
Building & Improvements	4,946,855
Cost Capitalized Subsequent To Acquisition
Land	7,635
Building & Improvements	603,896
Gross Amount at Which Carried at Close of Period
Land	1,877,492
Building & Improvements	5,550,751
Total	7,428,243	$ 7,203,216	$ 6,670,210	$ 6,289,687
Accumulated Depreciation	1,267,598	$ 1,123,412	$ 983,273	$ 848,077
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	65,604
Gross Amount at Which Carried at Close of Period
Land	114,077
Building & Improvements	541,990
Total	656,067
Accumulated Depreciation	131,946
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	11,527
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	74,222
Total	74,222
Accumulated Depreciation	24,449
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	37,283
Gross Amount at Which Carried at Close of Period
Land	51,093
Building & Improvements	243,255
Total	294,348
Accumulated Depreciation	78,460
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	24,315
Gross Amount at Which Carried at Close of Period
Land	223,529
Building & Improvements	1,057,513
Total	1,281,042
Accumulated Depreciation	$ 245,932
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	50,261
Gross Amount at Which Carried at Close of Period
Land	18,846
Building & Improvements	128,965
Total	147,811
Accumulated Depreciation	53,036
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	36,857
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	765,070
Total	765,070
Accumulated Depreciation	198,483
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	0
Building & Improvements	32,612
Gross Amount at Which Carried at Close of Period
Land	91,038
Building & Improvements	413,356
Total	504,394
Accumulated Depreciation	102,335
1100 King Street - 1-6 International Drive
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	49,392
Building & Improvements	104,376
Cost Capitalized Subsequent To Acquisition
Land	2,473
Building & Improvements	17,612
Gross Amount at Which Carried at Close of Period
Land	51,865
Building & Improvements	121,988
Total	173,853
Accumulated Depreciation	31,007
520 White Plains Road
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	6,324
Building & Improvements	26,096
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,720
Gross Amount at Which Carried at Close of Period
Land	6,324
Building & Improvements	32,816
Total	39,140
Accumulated Depreciation	8,617
115-117 Stevens Avenue
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	5,933
Building & Improvements	23,826
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	5,797
Gross Amount at Which Carried at Close of Period
Land	5,933
Building & Improvements	29,623
Total	35,556
Accumulated Depreciation	7,916
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	7,402
Gross Amount at Which Carried at Close of Period
Land	10,526
Building & Improvements	50,511
Total	61,037
Accumulated Depreciation	13,567
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	8,223
Gross Amount at Which Carried at Close of Period
Land	11,183
Building & Improvements	56,129
Total	67,312
Accumulated Depreciation	14,714
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	5,456
Gross Amount at Which Carried at Close of Period
Land	9,777
Building & Improvements	44,504
Total	54,281
Accumulated Depreciation	10,557
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	12,515
Gross Amount at Which Carried at Close of Period
Land	29,497
Building & Improvements	130,765
Total	160,262
Accumulated Depreciation	31,927
7 Landmark Square
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	2,088
Building & Improvements	7,748
Cost Capitalized Subsequent To Acquisition
Land	(367)
Building & Improvements	84
Gross Amount at Which Carried at Close of Period
Land	1,721
Building & Improvements	7,832
Total	9,553
Accumulated Depreciation	799
680 Washington Boulevard
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	11,696
Building & Improvements	45,364
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	5,818
Gross Amount at Which Carried at Close of Period
Land	11,696
Building & Improvements	51,182
Total	62,878
Accumulated Depreciation	$ 12,783
Interest in property (as a percent)	51.00%
750 Washington Boulevard
Real Estate And Accumulated Depreciation
Encumbrances	$ 0
Initial Cost
Land	16,916
Building & Improvements	68,849
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,459
Gross Amount at Which Carried at Close of Period
Land	16,916
Building & Improvements	75,308
Total	92,224
Accumulated Depreciation	$ 17,391
Interest in property (as a percent)	51.00%
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	5,223
Gross Amount at Which Carried at Close of Period
Land	7,747
Building & Improvements	35,646
Total	43,393
Accumulated Depreciation	8,732
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	5,297
Gross Amount at Which Carried at Close of Period
Land	13,516
Building & Improvements	58,525
Total	72,041
Accumulated Depreciation	13,747
400 Summit Lake Drive
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	38,889
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	285
Building & Improvements	1
Gross Amount at Which Carried at Close of Period
Land	39,174
Building & Improvements	1
Total	39,175
Accumulated Depreciation	1
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	8,157
Gross Amount at Which Carried at Close of Period
Land	36,677
Building & Improvements	154,111
Total	190,788
Accumulated Depreciation	37,473
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	0
Building & Improvements	15,868
Gross Amount at Which Carried at Close of Period
Land	34,000
Building & Improvements	62,279
Total	96,279
Accumulated Depreciation	12,203
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	8,122
Gross Amount at Which Carried at Close of Period
Land	54,489
Building & Improvements	83,741
Total	138,230
Accumulated Depreciation	10,341
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	49,534
Gross Amount at Which Carried at Close of Period
Land	24,343
Building & Improvements	86,692
Total	111,035
Accumulated Depreciation	1,462
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	1,888
Gross Amount at Which Carried at Close of Period
Land	45,976
Building & Improvements	69,204
Total	115,180
Accumulated Depreciation	7,308
315 West 33rd Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	195,834
Building & Improvements	164,429
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,173
Gross Amount at Which Carried at Close of Period
Land	195,834
Building & Improvements	170,602
Total	366,436
Accumulated Depreciation	10,246
16 Court Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	19,217
Building & Improvements	63,210
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	10,854
Gross Amount at Which Carried at Close of Period
Land	19,217
Building & Improvements	74,064
Total	93,281
Accumulated Depreciation	7,393
125 Chubb Way
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	5,884
Building & Improvements	25,958
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	24,482
Gross Amount at Which Carried at Close of Period
Land	5,884
Building & Improvements	50,440
Total	56,324
Accumulated Depreciation	7,200
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	1,343
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	247
Gross Amount at Which Carried at Close of Period
Land	11,078
Building & Improvements	45,046
Total	56,124
Accumulated Depreciation	1,788
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	515
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	55,365
Gross Amount at Which Carried at Close of Period
Land	120,900
Building & Improvements	245,079
Total	365,979
Accumulated Depreciation	43,887
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	38,779
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	285,452
Total	285,452
Accumulated Depreciation	87,625
102 Greene Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	8,215
Building & Improvements	26,717
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	277
Gross Amount at Which Carried at Close of Period
Land	8,215
Building & Improvements	26,994
Total	35,209
Accumulated Depreciation	847
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	38,618
Gross Amount at Which Carried at Close of Period
Land	19,844
Building & Improvements	81,117
Total	100,961
Accumulated Depreciation	$ 29,741
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	0
110 Greene Street
Real Estate And Accumulated Depreciation
Encumbrances	0
Initial Cost
Land	89,250
Building & Improvements	165,750
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	324
Gross Amount at Which Carried at Close of Period
Land	89,250
Building & Improvements	166,074
Total	255,324
Accumulated Depreciation	$ 1,827
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	79
Building & Improvements	4,692
Gross Amount at Which Carried at Close of Period
Land	1,209
Building & Improvements	4,692
Total	5,901
Accumulated Depreciation	$ 0