SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 25,433
Initial Cost to Company
Land	85,627
Buildings and Improvements	475,715
Costs Capitalized Subsequent to Acquisition, Net	107,657
Impairment/Write Downs	(6,878)
Cost Amount Carried at Close of Period
Land	85,627
Buildings and Improvements	576,494
Total	662,121
Accumulated Depreciation	202,700	$ 375,968	$ 450,718	$ 755,255
1225 Seventeenth Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company
Land	22,400
Buildings and Improvements	110,090
Costs Capitalized Subsequent to Acquisition, Net	35,357
Impairment/Write Downs	(2,751)
Cost Amount Carried at Close of Period
Land	22,400
Buildings and Improvements	142,696
Total	165,096
Accumulated Depreciation	40,542
1250 H Street, NW
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company
Land	5,975
Buildings and Improvements	53,778
Costs Capitalized Subsequent to Acquisition, Net	16,646
Impairment/Write Downs	(719)
Cost Amount Carried at Close of Period
Land	5,975
Buildings and Improvements	69,705
Total	75,680
Accumulated Depreciation	35,902
Georgetown-Green and Harris Buildings
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company
Land	24,000
Buildings and Improvements	35,979
Costs Capitalized Subsequent to Acquisition, Net	2,319
Impairment/Write Downs	0
Cost Amount Carried at Close of Period
Land	24,000
Buildings and Improvements	38,298
Total	62,298
Accumulated Depreciation	9,408
109 Brookline Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company
Land	3,168
Buildings and Improvements	30,397
Costs Capitalized Subsequent to Acquisition, Net	19,149
Impairment/Write Downs	(1,397)
Cost Amount Carried at Close of Period
Land	3,168
Buildings and Improvements	48,149
Total	51,317
Accumulated Depreciation	23,248
206 East 9th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	25,433
Initial Cost to Company
Land	7,900
Buildings and Improvements	38,533
Costs Capitalized Subsequent to Acquisition, Net	5,996
Impairment/Write Downs	(655)
Cost Amount Carried at Close of Period
Land	7,900
Buildings and Improvements	43,874
Total	51,774
Accumulated Depreciation	8,560
Bridgepoint Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company
Land	7,784
Buildings and Improvements	70,526
Costs Capitalized Subsequent to Acquisition, Net	25,382
Impairment/Write Downs	(1,323)
Cost Amount Carried at Close of Period
Land	7,784
Buildings and Improvements	94,585
Total	102,369
Accumulated Depreciation	48,381
333 108th Avenue NE
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost to Company
Land	14,400
Buildings and Improvements	136,412
Costs Capitalized Subsequent to Acquisition, Net	2,808
Impairment/Write Downs	(33)
Cost Amount Carried at Close of Period
Land	14,400
Buildings and Improvements	139,187
Total	153,587
Accumulated Depreciation	$ 36,659