Debt - Summary of Outstanding Debt (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	May 03, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate	4.60%
Notes and mortgages payable	$ 3,039,149		$ 2,941,524
Credit Facility	50,000		20,000
Less: deferred financing costs	(22,552)		(18,914)
Total notes and mortgages payable, net	$ 3,016,597		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	1.77%
Credit Facility	$ 50,000		20,000
1633 Broadway [Member]
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate	3.52%
Notes and mortgages 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%
Notes and mortgages 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	2.27%
Notes and mortgages payable	$ 13,544		13,544
900 Third Avenue [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-11
Notes and mortgages payable, Interest Rate	4.26%
Notes and mortgages 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%
Notes and mortgages 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	1.79%
Notes and mortgages payable	$ 112,337		112,337
31 West 52nd Street [Member]
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate	3.80%
Notes and mortgages payable	$ 500,000		413,490
31 West 52nd Street [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2026-05
Notes and mortgages payable, Interest Rate	3.80%	3.80%
Notes and mortgages payable	$ 500,000		237,600
31 West 52nd Street [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Notes and mortgages payable			175,890
One Market Plaza [Member]
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate	6.12%
Notes and mortgages payable	$ 869,226		857,037
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	6.13%
Notes and mortgages payable	$ 859,648		857,037
One Market Plaza [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt	2019-12
Notes and mortgages payable, Interest Rate	4.73%
Notes and mortgages payable	$ 9,578
Waterview [Member]
Debt Instrument [Line Items]
Maturity date of debt	2017-06
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%
Notes and mortgages 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%
Notes and mortgages payable	$ 88,042		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%
Notes and mortgages payable	$ 84,000		$ 84,000