Segments - Schedule of NOI for Each Reportable Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Property-related revenues	$ 191,158	$ 188,517	$ 561,321	$ 555,333
Property-related operating expenses	(71,648)	(69,811)	(207,601)	(206,435)
NOI from unconsolidated joint ventures	4,973	4,448	14,569	13,757
NOI	124,483	123,154	368,289	362,655
New York [Member]
Segment Reporting Information [Line Items]
Property-related revenues	122,365	118,539	362,202	347,720
Property-related operating expenses	(49,825)	(48,257)	(144,432)	(140,710)
NOI from unconsolidated joint ventures	2,776	4,356	10,319	13,514
NOI	75,316	74,638	228,089	220,524
San Francisco [Member]
Segment Reporting Information [Line Items]
Property-related revenues	61,999	57,568	177,614	164,811
Property-related operating expenses	(18,068)	(15,206)	(51,893)	(44,370)
NOI from unconsolidated joint ventures	2,106		4,019
NOI	46,037	42,362	129,740	120,441
Washington, D.C. [Member]
Segment Reporting Information [Line Items]
Property-related revenues	7,064	12,685	21,707	43,569
Property-related operating expenses	(2,802)	(4,782)	(8,558)	(16,363)
NOI	4,262	7,903	13,149	27,206
Other [Member]
Segment Reporting Information [Line Items]
Property-related revenues	(270)	(275)	(202)	(767)
Property-related operating expenses	(953)	(1,566)	(2,718)	(4,992)
NOI from unconsolidated joint ventures	91	92	231	243
NOI	$ (1,132)	$ (1,749)	$ (2,689)	$ (5,516)