Debt - Summary of Outstanding Debt (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Notes and Mortgages payable, Interest Rate	4.68%
Mortgages and notes payable	$ 2,942,026	$ 2,941,524
Credit Facility	40,000	20,000
Less: deferred financing costs	(18,192)	(18,914)
Total notes and mortgages payable, net	$ 2,923,834	2,922,610
Credit Facility With Variable Rate [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity date of debt	2018-11
Interest Rate	1.69%
Credit Facility	$ 40,000	20,000
1633 Broadway [Member]
Debt Instrument [Line Items]
Notes and Mortgages payable, Interest Rate	3.52%
Mortgages and notes payable	$ 1,013,544	1,013,544
1633 Broadway [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2022-12
Notes and Mortgages payable, Interest Rate	3.54%
Mortgages and notes payable	$ 1,000,000	1,000,000
1633 Broadway [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2022-12
Notes and Mortgages payable, Interest Rate	2.19%
Mortgages and notes payable	$ 13,544	13,544
900 Third Avenue [Member]
Debt Instrument [Line Items]
Notes and Mortgages payable, Interest Rate	4.23%
Mortgages and notes payable	$ 274,337	274,337
900 Third Avenue [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-11
Notes and Mortgages payable, Interest Rate	5.98%
Mortgages and notes payable	$ 162,000	162,000
900 Third Avenue [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-11
Notes and Mortgages payable, Interest Rate	1.70%
Mortgages and notes payable	$ 112,337	112,337
31 West 52nd Street [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-12
Notes and Mortgages payable, Interest Rate	4.23%
Mortgages and notes payable	$ 413,490	413,490
31 West 52nd Street [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-12
Notes and Mortgages payable, Interest Rate	6.04%
Mortgages and notes payable	$ 237,600	237,600
31 West 52nd Street [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-12
Notes and Mortgages payable, Interest Rate	1.78%
Mortgages and notes payable	$ 175,890	175,890
One Market Plaza [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2019-12
Notes and Mortgages payable, Interest Rate	6.14%
Mortgages and notes payable	$ 857,893	857,037
Waterview [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-06
Notes and Mortgages payable, Interest Rate	5.76%
Mortgages and notes payable	$ 210,000	210,000
1899 Pennsylvania Avenue [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2020-11
Notes and Mortgages payable, Interest Rate	4.88%
Mortgages and notes payable	$ 88,762	89,116
Liberty Place [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2018-06
Notes and Mortgages payable, Interest Rate	4.50%
Mortgages and notes payable	$ 84,000	$ 84,000