Segments - Schedule of NOI for Each Reportable Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Property-related revenues	$ 173,936	$ 167,342	$ 518,872	$ 504,971
Property-related operating expenses	(68,264)	(64,025)	(197,696)	(186,964)
NOI from unconsolidated joint ventures	4,993	3,974	14,774	12,938
NOI	110,665	107,291	335,950	330,945
New York [Member]
Segment Reporting Information [Line Items]
Property-related revenues	109,493	113,029	321,419	346,683
Property-related operating expenses	(46,609)	(45,748)	(134,657)	(132,428)
NOI from unconsolidated joint ventures	4,815	3,893	14,406	12,696
NOI	67,699	71,174	201,168	226,951
Washington, D.C. [Member]
Segment Reporting Information [Line Items]
Property-related revenues	14,986	22,229	56,911	63,689
Property-related operating expenses	(5,887)	(8,322)	(21,376)	(24,691)
NOI	9,099	13,907	35,535	38,998
San Francisco [Member]
Segment Reporting Information [Line Items]
Property-related revenues	49,758	31,441	139,898	92,762
Property-related operating expenses	(14,164)	(7,994)	(35,889)	(22,426)
NOI	35,594	23,447	104,009	70,336
Other [Member]
Segment Reporting Information [Line Items]
Property-related revenues	(301)	643	644	1,837
Property-related operating expenses	(1,604)	(1,961)	(5,774)	(7,419)
NOI from unconsolidated joint ventures	178	81	368	242
NOI	$ (1,727)	$ (1,237)	$ (4,762)	$ (5,340)