Debt - Summary of Outstanding Interest Rate Swaps (Details) - USD ($)	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Interest rate swap liabilities	$ 160,473,000	$ 194,196,000
Interest Rate Swap [Member]
Derivative [Line Items]
Interest rate swap liabilities	160,473,000	194,196,000
1633 Broadway [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount	$ 772,100,000
Maturity Date	2016-12
Strike Rate	4.92%
Interest rate swap liabilities	$ 46,929,000	60,191,000
1633 Broadway [Member] | Minimum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2006-12
1633 Broadway [Member] | Maximum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2008-06
900 Third Avenue [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount	$ 255,000,000
Strike Rate	4.15%
Interest rate swap liabilities	$ 15,884,000	19,158,000
900 Third Avenue [Member] | Minimum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2007-11
Maturity Date	2015-11
900 Third Avenue [Member] | Maximum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2012-11
Maturity Date	2017-11
31 West 52nd Street [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount	$ 337,500,000
Strike Rate	4.49%
Interest rate swap liabilities	$ 24,013,000	28,748,000
31 West 52nd Street [Member] | Minimum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2007-12
Maturity Date	2015-12
31 West 52nd Street [Member] | Maximum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2012-12
Maturity Date	2017-12
One Market Plaza [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Notional Amount	$ 840,000,000
Maturity Date	2017-07
Strike Rate	5.02%
Interest rate swap liabilities	$ 73,647,000	$ 86,099,000
One Market Plaza [Member] | Minimum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2007-08
One Market Plaza [Member] | Maximum [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective Dates	2012-08