Segments - Schedule of NOI for Each Reportable Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Property-related revenues	$ 186,010	$ 173,256	$ 366,816	$ 344,936
Property-related operating expenses	(67,646)	(63,461)	(136,624)	(129,432)
NOI from unconsolidated joint ventures	4,569	4,958	9,309	9,781
NOI	122,933	114,753	239,501	225,285
New York [Member]
Segment Reporting Information [Line Items]
Property-related revenues	115,536	106,602	229,181	211,926
Property-related operating expenses	(45,292)	(43,289)	(92,453)	(88,048)
NOI from unconsolidated joint ventures	4,493	4,838	9,158	9,591
NOI	74,737	68,151	145,886	133,469
Washington, D.C. [Member]
Segment Reporting Information [Line Items]
Property-related revenues	15,435	18,138	30,884	41,925
Property-related operating expenses	(5,736)	(6,565)	(11,581)	(15,489)
NOI	9,699	11,573	19,303	26,436
San Francisco [Member]
Segment Reporting Information [Line Items]
Property-related revenues	55,344	48,201	107,243	90,140
Property-related operating expenses	(15,048)	(11,120)	(29,164)	(21,725)
NOI	40,296	37,081	78,079	68,415
Other [Member]
Segment Reporting Information [Line Items]
Property-related revenues	(305)	315	(492)	945
Property-related operating expenses	(1,570)	(2,487)	(3,426)	(4,170)
NOI from unconsolidated joint ventures	76	120	151	190
NOI	$ (1,799)	$ (2,052)	$ (3,767)	$ (3,035)