Significant Accounting Policies (Details 4)	6 Months Ended		3 Months Ended
	Jun. 30, 2012 option statement	Jun. 30, 2012 Customer concentration tenant	Jun. 30, 2012 Credit concentration	Jun. 30, 2012 Annualized rent 1185 Avenue of the Americas. Customer concentration	Jun. 30, 2012 Annualized rent One Madison Avenue Customer concentration	Jun. 30, 2012 Annualized rent 420 Lexington Avenue Customer concentration	Jun. 30, 2012 Annualized rent 1515 Broadway Customer concentration	Jun. 30, 2012 Annualized rent Three tenant Customer concentration	Jun. 30, 2012 Annualized rent Tenant 1 Customer concentration	Jun. 30, 2012 Annualized rent Tenant 2 Customer concentration	Jun. 30, 2012 Annualized rent Tenant 3 Customer concentration
Concentration of Credit Risk
Number of tenants		3
Maximum percentage of annualized rent for any one tenant not individually disclosed								1.90%
Percentage of concentration				6.00%	6.00%	5.00%	9.00%		7.40%	6.90%	6.00%
Minimum revenue on debt and preferred equity investments (as a percent)			10.00%
Number of options for presenting other comprehensive income (OCI)	2
Number of statements in which statement of total comprehensive income can be presented	2