Debt Schedule of Long term Debt (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Total	$ 873,863		$ 883,112
Mortgages [Member]
Debt Instrument [Line Items]
Fixed rate debt	826,230		835,647
Floating rate debt	402,633		372,465
Total	1,228,863		1,208,112
Mortgages [Member] | 501 Seventh Avenue [Member]
Debt Instrument [Line Items]
Fixed rate debt	39,026	[1]	0	[1]
Stated Rate	5.80%	[1]
Effective Rate	5.89%	[1],[2]
Mortgages [Member] | 501 Seventh Avenue - Note 1 [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	1,037	[1]
Mortgages [Member] | 501 Seventh Avenue - Note 2 - Tranche 1 [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	31,459	[1]
Mortgages [Member] | 501 Seventh Avenue - Note 2 - Tranche 2 [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	6,889	[1]
Mortgages [Member] | 1359 Broadway [Member]
Debt Instrument [Line Items]
Fixed rate debt	44,276	[1]	0	[1]
Stated Rate	6.04%
Effective Rate	6.45%	[2]
Mortgages [Member] | 1359 Broadway - First Lien [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	9,579	[1]
Mortgages [Member] | 1359 Broadway - Second Lien - Tranche 1 [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	5,561	[1]
Mortgages [Member] | 1359 Broadway - Second Lien - Tranche 2 [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	11,311	[1]
Mortgages [Member] | 1359 Broadway - Second Lien - Tranche 3 [Member]
Debt Instrument [Line Items]
Fixed rate debt	0	[1]	18,572	[1]
Mortgages [Member] | One Grand Central Place - First Lien [Member]
Debt Instrument [Line Items]
Fixed rate debt	70,578		71,723
Stated Rate	5.34%
Effective Rate	5.98%	[2]
Mortgages [Member] | One Grand Central Place - Second Lien [Member]
Debt Instrument [Line Items]
Fixed rate debt	14,724		14,884
Stated Rate	7.00%
Effective Rate	7.64%	[2]
Mortgages [Member] | 500 Mamaroneck Avenue [Member]
Debt Instrument [Line Items]
Fixed rate debt	32,260		32,620
Stated Rate	5.41%
Effective Rate	6.58%	[2]
Mortgages [Member] | 250 West 57th Street - First Lien [Member]
Debt Instrument [Line Items]
Fixed rate debt	25,194		25,621
Stated Rate	5.33%
Effective Rate	5.82%	[2]
Mortgages [Member] | 250 West 57th Street - Second Lien [Member]
Debt Instrument [Line Items]
Fixed rate debt	11,109		11,252
Stated Rate	6.13%
Effective Rate	6.62%	[2]
Mortgages [Member] | Metro Center [Member]
Debt Instrument [Line Items]
Fixed rate debt	95,062		96,158
Stated Rate	5.89%
Effective Rate	6.24%	[2]
Mortgages [Member] | 10 Union Square [Member]
Debt Instrument [Line Items]
Fixed rate debt	20,807		20,972
Stated Rate	6.00%
Effective Rate	6.65%	[2]
Mortgages [Member] | 10 Bank Street [Member]
Debt Instrument [Line Items]
Fixed rate debt	33,150		33,444
Stated Rate	5.72%
Effective Rate	6.15%	[2]
Mortgages [Member] | 1542 Third Avenue [Member]
Debt Instrument [Line Items]
Fixed rate debt	18,820		19,011
Stated Rate	5.90%
Effective Rate	6.49%	[2]
Mortgages [Member] | First Stamford Place [Member]
Debt Instrument [Line Items]
Fixed rate debt	243,966		245,629
Stated Rate	5.65%
Effective Rate	6.26%	[2]
Mortgages [Member] | 1010 Third Avenue and 77 West 55th Street [Member]
Debt Instrument [Line Items]
Fixed rate debt	27,849		28,096
Stated Rate	5.69%
Effective Rate	6.17%	[2]
Mortgages [Member] | 383 Main Avenue [Member]
Debt Instrument [Line Items]
Fixed rate debt	30,131		30,403
Stated Rate	5.59%
Effective Rate	5.95%	[2]
Mortgages [Member] | 1333 Broadway [Member]
Debt Instrument [Line Items]
Fixed rate debt	76,733	[3]	78,121
Stated Rate	6.32%
Effective Rate	6.54%	[2]
Unamortized premium	6,715
Mortgages [Member] | 1350 Broadway - First Lien Mortgage Loan [Member]
Debt Instrument [Line Items]
Fixed rate debt	42,545	[4]	43,305
Stated Rate	5.87%
Effective Rate	6.20%	[2]
Unamortized premium	3,381
Mortgages [Member] | 501 Seventh Avenue - Third Lien [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Floating rate debt	6,540		6,540
Basis spread on variable rate	2.00%	[5]
Interest rate at end of period	2.16%	[5]
Mortgages [Member] | 1350 Broadway - 2nd Lien Mortgage Loan [Member]
Debt Instrument [Line Items]
Floating rate debt	13,711	[6]	13,543
Unamortized premium	34
Mortgages [Member] | 1350 Broadway - 2nd Lien Mortgage Loan [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Stated Rate			4.25%	[7]
Basis spread on variable rate	1.00%	[7]
Interest rate at end of period	4.25%	[7]
Mortgages [Member] | One Grand Central Place - Third Lien [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Floating rate debt	6,382		6,382
Stated Rate	3.75%	[8]
Basis spread on variable rate	0.50%	[8]
Interest rate at end of period	3.75%	[8]
Mortgages [Member] | 250 West 57th Street - Third lien [Member]
Debt Instrument [Line Items]
Stated Rate	4.25%	[9]
Basis spread on variable rate	1.00%	[9]
Interest rate at end of period	4.25%	[9]
Principal outstanding minimum increments	5,000	[9]
Mortgages [Member] | 250 West 57th Street - Third lien [Member] | Interest Rate Fix Option 1 [Member]
Debt Instrument [Line Items]
Stated Rate	4.75%	[9]
Basis spread on variable rate	3.00%	[9]
Number of days prior to the Effective date to fix the interest rate	2 days	[9]
Mortgages [Member] | 250 West 57th Street - Third lien [Member] | Interest Rate Fix Option 2 [Member]
Debt Instrument [Line Items]
Stated Rate	5.00%	[9]
Basis spread on variable rate	3.00%	[9]
Number of days prior to the Effective date to fix the interest rate	30 days	[9]
Mortgages [Member] | 250 West 57th Street - Third lien [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Floating rate debt	21,000		21,000
Mortgages [Member] | Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Floating rate debt	55,000		25,000
Mortgages [Member] | Secured Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.20%	[10]
Interest rate at end of period	1.36%	[10]
Mortgages [Member] | Secured Term Credit Facility [Member]
Debt Instrument [Line Items]
Floating rate debt	$ 300,000		$ 300,000
Mortgages [Member] | Secured Term Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	1.35%	[11]
Interest rate at end of period	1.52%	[11]

[1] The loan was consolidated in February 2014.

[2] The effective rate is the yield as of June 30, 2014, including the effects of debt issuance costs.

[3] Includes unamortized premium of $6,715.

[4] Includes unamortized premium of $3,381.

[5] Floating at 30 day LIBOR plus 2.0%. The rate as of June 30, 2014 was 2.16%.

[6] ncludes unamortized premium of $34.

[7] Interest at the greater of 4.25% and Prime plus 1%. The rate at June 30, 2014 was 4.25%.

[8] Interest at the greater of Prime plus 0.50% and 3.75%. The rate as of June 30, 2014 was 3.75%.

[9] 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 June 30, 2014 was 4.25%.

[10] Floating at 30 day LIBOR plus 1.20%. The rate as of June 30, 2014 was 1.36%.

[11] Floating at 30 day LIBOR plus 1.35%. The rate at June 30, 2014 was 1.52%.