Debt - Summary of Outstanding Debt (Details) - USD ($) $ in Thousands			12 Months Ended
	Jan. 10, 2018	Jan. 09, 2018	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate			3.72%
Notes and mortgages payable			$ 3,599,800	$ 3,583,100
Credit Facility			0	0
Less: deferred financing costs			(32,883)	(41,800)
Total notes and mortgages payable, net			$ 3,566,917	3,541,300
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity date of debt	2022-01	2018-11
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Fixed/Variable Rate	1.15%	1.25%
Credit Facility With Variable Rate [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maturity date of debt			2022-01
Credit Facility With Variable Rate [Member] | London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Fixed/Variable Rate			1.15%
1633 Broadway [Member]
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate			3.56%
Notes and mortgages payable			$ 1,046,800	1,030,100
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			4.10%
Notes and mortgages payable			$ 46,800	30,100
1633 Broadway [Member] | Mortgages and Notes Payable with Variable Rate [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Fixed/Variable Rate			1.75%
One Market Plaza [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt			2024-02
Notes and mortgages payable, Interest Rate			4.03%
Notes and mortgages payable			$ 975,000	975,000
1301 Avenue of Americas [Member]
Debt Instrument [Line Items]
Notes and mortgages payable, Interest Rate			3.51%
Notes and mortgages payable			$ 850,000	850,000
1301 Avenue of Americas [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt			2021-11
Notes and mortgages payable, Interest Rate			3.05%
Notes and mortgages payable			$ 500,000	500,000
1301 Avenue of Americas [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt			2021-11
Notes and mortgages payable, Interest Rate			4.18%
Notes and mortgages payable			$ 350,000	350,000
1301 Avenue of Americas [Member] | Mortgages and Notes Payable with Variable Rate [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Fixed/Variable Rate			1.80%
50 Beale Street [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Maturity date of debt			2021-10
Notes and mortgages payable, Interest Rate			3.65%
Notes and mortgages payable			$ 228,000	228,000
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%
Notes and mortgages payable			$ 500,000	$ 500,000