Debt Schedule of Long term Debt (Details) (USD $)																																																																																							12 Months Ended						12 Months Ended				12 Months Ended			12 Months Ended			12 Months Ended										12 Months Ended				12 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Mortgages [Member]	Dec. 31, 2012 Mortgages [Member]	Dec. 31, 2013 Mortgages [Member] 501 Seventh Avenue - Note 1 [Member]		Dec. 31, 2012 Mortgages [Member] 501 Seventh Avenue - Note 1 [Member]	Dec. 31, 2013 Mortgages [Member] 501 Seventh Avenue - Note 2 - Tranche 1 [Member] tranche		Dec. 31, 2012 Mortgages [Member] 501 Seventh Avenue - Note 2 - Tranche 1 [Member]		Dec. 31, 2013 Mortgages [Member] 501 Seventh Avenue - Note 2 - Tranche 2 [Member]		Dec. 31, 2012 Mortgages [Member] 501 Seventh Avenue - Note 2 - Tranche 2 [Member]		Dec. 31, 2013 Mortgages [Member] 1359 Broadway - First Lien [Member]		Dec. 31, 2012 Mortgages [Member] 1359 Broadway - First Lien [Member]	Dec. 31, 2013 Mortgages [Member] 1359 Broadway - Second Lien - Tranche 1 [Member]		Dec. 31, 2012 Mortgages [Member] 1359 Broadway - Second Lien - Tranche 1 [Member]		Dec. 31, 2013 Mortgages [Member] 1359 Broadway - Second Lien - Tranche 2 [Member] tranche		Dec. 31, 2012 Mortgages [Member] 1359 Broadway - Second Lien - Tranche 2 [Member]		Dec. 31, 2013 Mortgages [Member] 1359 Broadway - Second Lien - Tranche 3 [Member]		Dec. 31, 2012 Mortgages [Member] 1359 Broadway - Second Lien - Tranche 3 [Member]		Dec. 31, 2013 Mortgages [Member] One Grand Central Place - First Lien [Member]		Dec. 31, 2012 Mortgages [Member] One Grand Central Place - First Lien [Member]	Dec. 31, 2013 Mortgages [Member] One Grand Central Place - Second Lien [Member]		Dec. 31, 2012 Mortgages [Member] One Grand Central Place - Second Lien [Member]		Dec. 31, 2013 Mortgages [Member] 500 Mamaroneck Avenue [Member]		Dec. 31, 2012 Mortgages [Member] 500 Mamaroneck Avenue [Member]	Dec. 31, 2013 Mortgages [Member] 250 West 57th Street - First Lien [Member]		Dec. 31, 2012 Mortgages [Member] 250 West 57th Street - First Lien [Member]	Dec. 31, 2013 Mortgages [Member] 250 West 57th Street - Second Lien [Member]		Dec. 31, 2012 Mortgages [Member] 250 West 57th Street - Second Lien [Member]	Dec. 31, 2013 Mortgages [Member] Metro Center [Member]		Dec. 31, 2012 Mortgages [Member] Metro Center [Member]	Dec. 31, 2013 Mortgages [Member] Metro Center - Note 1 [Member]		Dec. 31, 2012 Mortgages [Member] Metro Center - Note 1 [Member]		Dec. 31, 2013 Mortgages [Member] Metro Center - Note 2 [Member]		Dec. 31, 2012 Mortgages [Member] Metro Center - Note 2 [Member]		Dec. 31, 2013 Mortgages [Member] 10 Union Square [Member]		Dec. 31, 2012 Mortgages [Member] 10 Union Square [Member]	Dec. 31, 2013 Mortgages [Member] 10 Bank Street [Member]		Dec. 31, 2012 Mortgages [Member] 10 Bank Street [Member]	Dec. 31, 2013 Mortgages [Member] 1542 Third Avenue [Member]		Dec. 31, 2012 Mortgages [Member] 1542 Third Avenue [Member]	Dec. 31, 2013 Mortgages [Member] First Stamford Place [Member]		Dec. 31, 2012 Mortgages [Member] First Stamford Place [Member]	Dec. 31, 2013 Mortgages [Member] 1010 Third Avenue and 77 West 55th Street [Member]		Dec. 31, 2012 Mortgages [Member] 1010 Third Avenue and 77 West 55th Street [Member]	Dec. 31, 2013 Mortgages [Member] 383 Main Avenue [Member]		Dec. 31, 2012 Mortgages [Member] 383 Main Avenue [Member]	Dec. 31, 2013 Mortgages [Member] 1333 Broadway [Member]		Dec. 31, 2012 Mortgages [Member] 1333 Broadway [Member]	Dec. 31, 2013 Mortgages [Member] 1350 Broadway - First Lien Mortgage Loan [Member]		Dec. 31, 2012 Mortgages [Member] 1350 Broadway - First Lien Mortgage Loan [Member]	Dec. 31, 2013 Mortgages [Member] 69 - 97 Main Street - Fixed Rate [Member]		Apr. 30, 2013 Mortgages [Member] 69 - 97 Main Street - Fixed Rate [Member]		Dec. 31, 2012 Mortgages [Member] 69 - 97 Main Street - Fixed Rate [Member]		Dec. 31, 2013 Mortgages [Member] 501 Seventh Avenue - Third Lien [Member] LIBOR [Member]		Dec. 31, 2012 Mortgages [Member] 501 Seventh Avenue - Third Lien [Member] LIBOR [Member]	Dec. 31, 2013 Mortgages [Member] 1350 Broadway - 2nd Lien Mortgage Loan [Member]		Dec. 31, 2012 Mortgages [Member] 1350 Broadway - 2nd Lien Mortgage Loan [Member]	Dec. 31, 2013 Mortgages [Member] 1350 Broadway - 2nd Lien Mortgage Loan [Member] Prime Rate [Member]		Dec. 31, 2012 Mortgages [Member] 1350 Broadway - 2nd Lien Mortgage Loan [Member] Prime Rate [Member]		Dec. 31, 2013 Mortgages [Member] The Empire State Building [Member] LIBOR [Member]		Dec. 31, 2012 Mortgages [Member] The Empire State Building [Member] LIBOR [Member]	Dec. 31, 2013 Mortgages [Member] One Grand Central Place - Third Lien [Member] Prime Rate [Member]		Dec. 31, 2012 Mortgages [Member] One Grand Central Place - Third Lien [Member] Prime Rate [Member]	Dec. 31, 2013 Mortgages [Member] 250 West 57th Street - Third lien [Member]		Dec. 31, 2013 Mortgages [Member] 250 West 57th Street - Third lien [Member] Interest Rate Fix Option 1 [Member]		Dec. 31, 2013 Mortgages [Member] 250 West 57th Street - Third lien [Member] Interest Rate Fix Option 2 [Member]		Dec. 31, 2013 Mortgages [Member] 250 West 57th Street - Third lien [Member] Prime Rate [Member]	Dec. 31, 2012 Mortgages [Member] 250 West 57th Street - Third lien [Member] Prime Rate [Member]	Dec. 31, 2013 Mortgages [Member] Secured Revolving Credit Facility [Member]	Dec. 31, 2012 Mortgages [Member] Secured Revolving Credit Facility [Member]	Dec. 31, 2013 Mortgages [Member] Secured Revolving Credit Facility [Member] LIBOR [Member]		Dec. 31, 2013 Mortgages [Member] Secured Term Credit Facility [Member]	Dec. 31, 2012 Mortgages [Member] Secured Term Credit Facility [Member]	Dec. 31, 2013 Mortgages [Member] Secured Term Credit Facility [Member] LIBOR [Member]
Debt Instrument [Line Items]
Fixed rate debt		$ 835,647,000	$ 737,675,000	$ 1,037,000		$ 1,075,000	$ 31,459,000	[1]	$ 32,589,000	[1]	$ 6,889,000	[1]	$ 7,107,000	[1]	$ 9,579,000		$ 9,922,000	$ 5,561,000	[2]	$ 5,761,000	[2]	$ 11,311,000	[2]	$ 11,689,000	[2]	$ 18,572,000	[2]	$ 19,068,000	[2]	$ 71,723,000		$ 73,922,000	$ 14,884,000	[3]	$ 15,187,000	[3]	$ 32,620,000		$ 33,256,000	$ 25,621,000		$ 26,442,000	$ 11,252,000		$ 11,524,000	$ 96,158,000		$ 0	$ 0	[4]	$ 59,937,000	[4]	$ 0	[4]	$ 38,151,000	[4]	$ 20,972,000		$ 21,284,000	$ 33,444,000		$ 33,963,000	$ 19,011,000		$ 19,370,000	$ 245,629,000		$ 248,716,000	$ 28,096,000		$ 28,570,000	$ 30,403,000		$ 30,924,000	$ 78,121,000	[5]	$ 0	$ 43,305,000	[6]	$ 0	$ 0	[7]			$ 9,218,000	[7]
Floating rate debt		372,465,000	240,475,000																																																																																				6,540,000		6,540,000	13,543,000	[8]	0					0		219,000,000	6,382,000		0							21,000,000	14,935,000	25,000,000	0			300,000,000	0
Total	883,112,000	1,208,112,000	978,150,000
Stated Rate				5.75%			5.75%	[1]			6.04%	[1]			5.75%			5.75%	[2]			5.87%	[2]			6.40%	[2]			5.34%			7.00%	[3]			5.41%			5.33%			6.13%			5.89%			5.80%	[4]			6.02%	[4]			6.00%			5.72%			5.90%			5.65%			5.69%			5.59%			6.32%			5.87%			5.64%	[7]													4.25%	[9]				3.75%	[10]		4.25%	[11]	4.75%	[11]	5.00%	[11]
Effective Rate				6.28%	[12]		6.28%	[1],[12]			6.55%	[1],[12]			6.24%	[12]		6.25%	[12],[2]			6.36%	[12],[2]			6.86%	[12],[2]			6.38%	[12]		6.72%	[12],[3]			6.70%	[12]		6.92%	[12]		7.81%	[12]		6.15%	[12]		0.00%	[12],[4]			0.00%	[12],[4]			6.48%	[12]		5.94%	[12]		6.31%	[12]		5.82%	[12]		6.12%	[12]		5.72%	[12]		6.68%	[12]		6.02%	[12]		0.00%	[12],[7]
Number of tranches							2															3
Proceeds from long term debt																																																																		250,000,000.0																	9,500,000	[7]
Basis spread on variable rate																																																																																							2.00%	[13]					1.00%	[9]			2.50%	[14]		0.50%	[10]		1.00%	[11]	3.00%	[11]	3.00%	[11]					1.20%	[15]			1.35%	[16]
Interest rate at end of period																																																																																							2.17%	[13]							4.25%	[9]	2.67%	[14]		3.75%	[10]		4.25%	[11]									1.37%	[15]			1.52%	[16]
Principal outstanding minimum increments																																																																																																							5,000,000	[11]
Number of days prior to the Effective date to fix the interest rate																																																																																																									2 days	[11]	30 days	[11]
Unamortized premium																																																																											$ 7,674,000			$ 3,885,000												$ 134,000

[1] Represents the two tranches of the second lien mortgage loan.

[2] Represents three tranches of the second lien mortgage loan.

[3] Represents a second lien mortgage loan.

[4] Notes 1 and 2 were pari passu.

[5] Includes unamortized premium of $7,674.

[6] Includes unamortized premium of $3,885.

[7] This loan was paid off with the proceeds of a new $9.5 million floating rate loan which we closed on during April 2013 and which was subsequently repaid during December 2013.

[8] Includes unamortized premium of $134.

[9] Interest at the greater of 4.25% and Prime plus 1%. The rate at December 31, 2013 was 4.25%.

[10] Interest at the greater of Prime plus 0.50% and 3.75%. The rate as of December 31, 2013 was 3.75%.

[11] Interest at the greater of 4.25% and prime plus 1%. Prior to January 5, 2015, we have the option to fix the interest rate on all or any portion of the principal then outstanding, up to three times and in minimum increments of $5,000 to an annual rate equal to either (i) the greater of (a) 4.75% or (b) 300 basis points in excess of the weekly average yield on United States Treasury Securities adjusted to a maturity closest to January 5, 2015 as most recently made available by the Federal Reserve Board as of two days prior to the effective date of the fixing of the interest rate, and (ii) the greater of (a) 5.00% or (b) 300 basis points in excess of the weekly average yield on United States Treasury Securities adjusted to a maturity closest to January 5, 2015 as most recently made available by the Federal Reserve Board as of 30 days prior to the effective date of the fixing of the interest rate. If option (i) is selected, we will be subject to the payment of pre‑payment fees, and if option (ii) is selected, we may prepay the loan without any pre‑payment fees. The rate as of December 31, 2013 was 4.25%.

[12] The effective rate is the yield as of December 31, 2013, including the effects of debt issuance costs.

[13] Floating at 30 day LIBOR plus 2.0%. The rate as of December 31, 2013 was 2.17%.

[14] Floating at 30 day LIBOR plus 2.5%. The rate as of December 31, 2013 was 2.67%. This loan was paid off with the proceeds of our secured revolving and term credit facility on October 7, 2013.

[15] Floating at 30 day LIBOR plus 1.20%. The rate as of December 31, 2013 was 1.37%.

[16] Floating at 30 day LIBOR plus 1.35%. The rate at December 31, 2013 was 1.52%.