Segments Disclosure - Schedule of NOI for Each Reportable Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Property-related revenues	$ 169,501	$ 159,691
Property-related operating expenses	(62,945)	(61,884)
NOI from unconsolidated joint ventures and funds	4,428	3,781
NOI	110,984	101,588
New York [Member]
Segment Reporting Information [Line Items]
Property-related revenues	119,303	113,953
Property-related operating expenses	(44,137)	(44,784)
NOI from unconsolidated joint ventures and funds	4,347	3,736
NOI	79,513	72,905
Washington, D.C. [Member]
Segment Reporting Information [Line Items]
Property-related revenues	19,982	19,151
Property-related operating expenses	(8,275)	(7,777)
NOI	11,707	11,374
San Francisco [Member]
Segment Reporting Information [Line Items]
Property-related revenues	29,619	25,816
Property-related operating expenses	(7,173)	(6,777)
NOI	22,446	19,039
Other [Member]
Segment Reporting Information [Line Items]
Property-related revenues	597	771
Property-related operating expenses	(3,360)	(2,546)
NOI from unconsolidated joint ventures and funds	81	45
NOI	$ (2,682)	$ (1,730)