Segment Information - Financial Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Real estate rental revenue	$ 73,227	$ 80,259	$ 222,889	$ 228,513
Real estate expenses	28,672	30,692	84,196	84,969
Net operating income	44,555	49,567	138,693	143,544
Depreciation and amortization	(30,470)	(37,340)	(89,789)	(97,441)
General and administrative expenses	(6,330)	(6,461)	(17,963)	(19,803)
Interest expense	(8,711)	(14,198)	(28,307)	(41,946)
Loss on sale of real estate	0	0	(7,539)	(1,046)
Gain on extinguishment of debt	0	0	262	0
Real estate impairment	0	0	0	(8,374)
Income from operations of properties sold or held for sale	0	2,942	0	16,158
Gain on sale of real estate	0	339,024	0	339,024
Loss on extinguishment of debt	0	(764)	0	(764)
Net (loss) income	(956)	332,770	(4,643)	329,352
Less: Net income attributable to noncontrolling interests in subsidiaries	0	0	0	0
Net (loss) income attributable to the controlling interests	(956)	332,770	(4,643)	329,352
Capital expenditures	13,110	12,150	38,686	30,905
Total assets	2,532,272	2,675,076	2,532,272	2,675,076	$ 2,628,328
Office | Reportable Segments
Segment Reporting Information [Line Items]
Real estate rental revenue	32,579	39,810	101,163	124,164
Real estate expenses	12,342	15,148	37,176	45,937
Net operating income	20,237	24,662	63,987	78,227
Capital expenditures	6,201	6,039	21,120	16,347
Total assets	1,056,074	1,191,838	1,056,074	1,191,838
Multifamily | Reportable Segments
Segment Reporting Information [Line Items]
Real estate rental revenue	36,266	35,790	108,882	90,012
Real estate expenses	14,988	14,232	43,083	34,928
Net operating income	21,278	21,558	65,799	55,084
Capital expenditures	6,520	5,742	15,477	12,841
Total assets	1,338,812	1,333,146	1,338,812	1,333,146
Corporate and Other
Segment Reporting Information [Line Items]
Real estate rental revenue	4,382	4,659	12,844	14,337
Real estate expenses	1,342	1,312	3,937	4,104
Net operating income	3,040	3,347	8,907	10,233
Capital expenditures	389	369	2,089	1,717
Total assets	$ 137,386	$ 150,092	$ 137,386	$ 150,092