Segments Disclosure - Schedule of NOI for Each Reportable Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Property-related revenues	$ 173,256	$ 168,128	$ 344,936	$ 337,629
Property-related operating expenses	(63,461)	(59,994)	(129,432)	(122,939)
NOI from unconsolidated joint ventures	4,958	4,536	9,781	8,964
NOI	114,753	112,670	225,285	223,654
New York [Member]
Segment Reporting Information [Line Items]
Property-related revenues	106,602	114,351	211,926	233,654
Property-related operating expenses	(43,289)	(42,543)	(88,048)	(86,680)
NOI from unconsolidated joint ventures	4,838	4,456	9,591	8,803
NOI	68,151	76,264	133,469	155,777
Washington, D.C. [Member]
Segment Reporting Information [Line Items]
Property-related revenues	18,138	21,478	41,925	41,460
Property-related operating expenses	(6,565)	(8,094)	(15,489)	(16,369)
NOI	11,573	13,384	26,436	25,091
San Francisco [Member]
Segment Reporting Information [Line Items]
Property-related revenues	48,201	31,702	90,140	61,321
Property-related operating expenses	(11,120)	(7,259)	(21,725)	(14,432)
NOI	37,081	24,443	68,415	46,889
Other [Member]
Segment Reporting Information [Line Items]
Property-related revenues	315	597	945	1,194
Property-related operating expenses	(2,487)	(2,098)	(4,170)	(5,458)
NOI from unconsolidated joint ventures	120	80	190	161
NOI	$ (2,052)	$ (1,421)	$ (3,035)	$ (4,103)