Schedule III - Real Estate and Accumulated Depreciation Schedule of Real Estate and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 903,985
Initial Cost to the Company
Land	199,287
Building & Improvements	918,018
Cost Capitalized Subsequent to Acquisition
Improvements	1,022,558
Gross Amount at which Carried
Land	201,196
Buildings & Improvements	1,938,667
Total	2,139,863	1,649,423	939,330	856,151
Accumulated Depreciation	(377,552)	(295,351)	(257,091)	(224,019)
112 West 34th Street [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	94,720
Initial Cost to the Company
Land	13,630
Building & Improvements	244,461
Cost Capitalized Subsequent to Acquisition
Improvements	4,936
Gross Amount at which Carried
Land	13,630
Buildings & Improvements	249,397
Total	263,027
Accumulated Depreciation	(4,092)
Location 1400 Broadway [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	85,256
Initial Cost to the Company
Land	0
Building & Improvements	96,338
Cost Capitalized Subsequent to Acquisition
Improvements	4,413
Gross Amount at which Carried
Land	0
Buildings & Improvements	100,750
Total	100,750
Accumulated Depreciation	(3,396)
1333 Broadway, New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	75,330
Initial Cost to the Company
Land	91,435
Building & Improvements	120,190
Cost Capitalized Subsequent to Acquisition
Improvements	2,582
Gross Amount at which Carried
Land	91,435
Buildings & Improvements	122,772
Total	214,207
Accumulated Depreciation	(5,243)
1350 Broadway, New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	41,831
Initial Cost to the Company
Land	0
Building & Improvements	102,518
Cost Capitalized Subsequent to Acquisition
Improvements	5,526
Gross Amount at which Carried
Land	0
Buildings & Improvements	108,044
Total	108,044
Accumulated Depreciation	(4,974)
250 West 57th Street, New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	2,117
Building & Improvements	5,041
Cost Capitalized Subsequent to Acquisition
Improvements	71,959
Gross Amount at which Carried
Land	2,117
Buildings & Improvements	77,000
Total	79,117
Accumulated Depreciation	(23,125)
501 Seventh Avenue, New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	1,100
Building & Improvements	2,600
Cost Capitalized Subsequent to Acquisition
Improvements	87,992
Gross Amount at which Carried
Land	1,100
Buildings & Improvements	90,592
Total	91,692
Accumulated Depreciation	(30,127)
1359 Broadway, New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	44,146
Initial Cost to the Company
Land	1,233
Building & Improvements	1,809
Cost Capitalized Subsequent to Acquisition
Improvements	45,398
Gross Amount at which Carried
Land	1,233
Buildings & Improvements	47,207
Total	48,440
Accumulated Depreciation	(17,187)
350 Fifth Avenue (Empire State Building), New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	21,551
Building & Improvements	38,934
Cost Capitalized Subsequent to Acquisition
Improvements	539,630
Gross Amount at which Carried
Land	21,551
Buildings & Improvements	578,564
Total	600,115
Accumulated Depreciation	(71,225)
One Grand Central Place, New York, NY [Member] | Office/Retail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	91,000
Initial Cost to the Company
Land	7,240
Building & Improvements	17,490
Cost Capitalized Subsequent to Acquisition
Improvements	161,039
Gross Amount at which Carried
Land	7,222
Buildings & Improvements	178,546
Total	185,768
Accumulated Depreciation	(66,999)
First Stamford Place, Stamford, CT [Member] | Office Building [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	242,294
Initial Cost to the Company
Land	22,952
Building & Improvements	122,739
Cost Capitalized Subsequent to Acquisition
Improvements	40,321
Gross Amount at which Carried
Land	24,861
Buildings & Improvements	161,150
Total	186,011
Accumulated Depreciation	(58,595)
One Station Place, Stamford, CT (Metro Center) [Member] | Office Building [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	99,845
Initial Cost to the Company
Land	5,313
Building & Improvements	28,602
Cost Capitalized Subsequent to Acquisition
Improvements	10,067
Gross Amount at which Carried
Land	5,313
Buildings & Improvements	38,669
Total	43,982
Accumulated Depreciation	(24,443)
383 Main Avenue, Norwalk, CT [Member] | Office Building [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	29,852
Initial Cost to the Company
Land	2,262
Building & Improvements	12,820
Cost Capitalized Subsequent to Acquisition
Improvements	11,145
Gross Amount at which Carried
Land	2,262
Buildings & Improvements	23,965
Total	26,227
Accumulated Depreciation	(9,125)
500 Mamaroneck Avenue, Harrison, NY [Member] | Office Building [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	4,571
Building & Improvements	25,915
Cost Capitalized Subsequent to Acquisition
Improvements	16,011
Gross Amount at which Carried
Land	4,571
Buildings & Improvements	41,925
Total	46,496
Accumulated Depreciation	(17,328)
10 Bank Street, White Plains, NY [Member] | Office Building [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	32,847
Initial Cost to the Company
Land	5,612
Building & Improvements	31,803
Cost Capitalized Subsequent to Acquisition
Improvements	10,813
Gross Amount at which Carried
Land	5,612
Buildings & Improvements	42,616
Total	48,228
Accumulated Depreciation	(16,032)
10 Union Square, New York, NY [Member] | Retail Site [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	20,641
Initial Cost to the Company
Land	5,003
Building & Improvements	12,866
Cost Capitalized Subsequent to Acquisition
Improvements	1,535
Gross Amount at which Carried
Land	5,003
Buildings & Improvements	14,401
Total	19,404
Accumulated Depreciation	(6,162)
1542 Third Avenue, New York, NY [Member] | Retail Site [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	18,628
Initial Cost to the Company
Land	2,239
Building & Improvements	15,266
Cost Capitalized Subsequent to Acquisition
Improvements	382
Gross Amount at which Carried
Land	2,239
Buildings & Improvements	15,648
Total	17,887
Accumulated Depreciation	(6,079)
1010 Third Avenue, New York, NY and 77 West 55th Street, New York, NY [Member] | Retail Site [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	27,595
Initial Cost to the Company
Land	4,462
Building & Improvements	15,817
Cost Capitalized Subsequent to Acquisition
Improvements	774
Gross Amount at which Carried
Land	4,462
Buildings & Improvements	16,593
Total	21,055
Accumulated Depreciation	(6,889)
69-97 Main Street, Westport, CT [Member] | Retail Site [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	2,782
Building & Improvements	15,766
Cost Capitalized Subsequent to Acquisition
Improvements	918
Gross Amount at which Carried
Land	2,782
Buildings & Improvements	16,684
Total	19,466
Accumulated Depreciation	(5,034)
103-107 Main Street, Westport, CT [Member] | Retail Site [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	1,243
Building & Improvements	7,043
Cost Capitalized Subsequent to Acquisition
Improvements	131
Gross Amount at which Carried
Land	1,260
Buildings & Improvements	7,157
Total	8,417
Accumulated Depreciation	(1,497)
Property for development at the Transportation Hub, Stamford, CT [Member] | Land [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to the Company
Land	4,542
Building & Improvements	0
Cost Capitalized Subsequent to Acquisition
Improvements	6,986
Gross Amount at which Carried
Land	4,542
Buildings & Improvements	6,986
Total	11,528
Accumulated Depreciation	$ 0