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Real Estate and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Real Estate Properties [Line Items]
Initial Basis	$ 984,390
Cost capitalized subsequent to acquisition	1,140,406
Land	511,482
Buildings	1,543,837
Construction in progress	69,477	$ 335,644
Total Purchase Price	2,124,796	2,081,597	$ 1,948,165	$ 1,803,200
Accumulated Depreciation	607,706	563,474	$ 525,518	$ 488,166
Book Value	1,517,090	1,518,123
Fixed rate mortgages	827,603	821,503
Development land, related debt	144,607	$ 108,623
Total, related debt	980,751
Shopping Centers
Real Estate Properties [Line Items]
Initial Basis	841,335
Cost capitalized subsequent to acquisition	461,349
Land	421,698
Buildings	873,788
Construction in progress	7,198
Total Purchase Price	1,302,684
Accumulated Depreciation	407,918
Book Value	894,766
Fixed rate mortgages	592,914
Shopping Centers | Ashbrook Marketplace, Ashburn, VA
Real Estate Properties [Line Items]
Initial Basis	8,938
Cost capitalized subsequent to acquisition	19,897
Land	8,938
Buildings	19,744
Construction in progress	153
Total Purchase Price	28,835
Accumulated Depreciation	453
Book Value	28,382
Fixed rate mortgages	$ 21,922
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Ashburn Village, Ashburn, VA
Real Estate Properties [Line Items]
Initial Basis	$ 11,431
Cost capitalized subsequent to acquisition	20,493
Land	6,764
Buildings	25,138
Construction in progress	22
Total Purchase Price	31,924
Accumulated Depreciation	14,989
Book Value	16,935
Fixed rate mortgages	$ 25,253
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Ashland Square Phase I, Dumfries, VA
Real Estate Properties [Line Items]
Initial Basis	$ 1,178
Cost capitalized subsequent to acquisition	5,298
Land	1,178
Buildings	5,298
Construction in progress	0
Total Purchase Price	6,476
Accumulated Depreciation	2,438
Book Value	4,038
Fixed rate mortgages	$ 0
Shopping Centers | Ashland Square Phase I, Dumfries, VA | Minimum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	20 years
Shopping Centers | Ashland Square Phase I, Dumfries, VA | Maximum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Beacon Center, Alexandria, VA
Real Estate Properties [Line Items]
Initial Basis	$ 24,161
Cost capitalized subsequent to acquisition	18,485
Land	22,691
Buildings	19,955
Construction in progress	0
Total Purchase Price	42,646
Accumulated Depreciation	15,823
Book Value	26,823
Fixed rate mortgages	$ 34,223
Shopping Centers | Beacon Center, Alexandria, VA | Minimum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Beacon Center, Alexandria, VA | Maximum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | BJ’s Wholesale Club, Alexandria, VA
Real Estate Properties [Line Items]
Initial Basis	$ 22,623
Cost capitalized subsequent to acquisition	0
Land	22,623
Buildings	0
Construction in progress	0
Total Purchase Price	22,623
Accumulated Depreciation	0
Book Value	22,623
Fixed rate mortgages	$ 10,018
Buildings and Improvements Depreciable Lives in Years	0 years
Shopping Centers | Boca Valley Plaza, Boca Raton, FL
Real Estate Properties [Line Items]
Initial Basis	$ 16,720
Cost capitalized subsequent to acquisition	2,614
Land	5,735
Buildings	13,599
Construction in progress	0
Total Purchase Price	19,334
Accumulated Depreciation	5,681
Book Value	13,653
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Boulevard, Fairfax, VA
Real Estate Properties [Line Items]
Initial Basis	$ 4,883
Cost capitalized subsequent to acquisition	4,709
Land	3,687
Buildings	5,905
Construction in progress	0
Total Purchase Price	9,592
Accumulated Depreciation	3,466
Book Value	6,126
Fixed rate mortgages	$ 15,191
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Briggs Chaney MarketPlace, Silver Spring, MD
Real Estate Properties [Line Items]
Initial Basis	$ 27,037
Cost capitalized subsequent to acquisition	4,711
Land	9,789
Buildings	21,959
Construction in progress	0
Total Purchase Price	31,748
Accumulated Depreciation	9,966
Book Value	21,782
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Broadlands Village, Ashburn, VA
Real Estate Properties [Line Items]
Initial Basis	$ 5,316
Cost capitalized subsequent to acquisition	35,823
Land	5,300
Buildings	35,826
Construction in progress	13
Total Purchase Price	41,139
Accumulated Depreciation	13,811
Book Value	27,328
Fixed rate mortgages	$ 30,467
Shopping Centers | Broadlands Village, Ashburn, VA | Minimum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Broadlands Village, Ashburn, VA | Maximum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Burtonsville Town Square, Burtonsville, MD
Real Estate Properties [Line Items]
Initial Basis	$ 74,212
Cost capitalized subsequent to acquisition	6,261
Land	28,401
Buildings	51,821
Construction in progress	251
Total Purchase Price	80,473
Accumulated Depreciation	5,184
Book Value	75,289
Fixed rate mortgages	$ 35,836
Shopping Centers | Burtonsville Town Square, Burtonsville, MD | Minimum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	20 years
Shopping Centers | Burtonsville Town Square, Burtonsville, MD | Maximum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	45 years
Shopping Centers | Countryside Marketplace, Sterling, VA
Real Estate Properties [Line Items]
Initial Basis	$ 28,912
Cost capitalized subsequent to acquisition	4,156
Land	7,666
Buildings	25,402
Construction in progress	0
Total Purchase Price	33,068
Accumulated Depreciation	11,364
Book Value	21,704
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Cranberry Square, Westminster, MD
Real Estate Properties [Line Items]
Initial Basis	$ 31,578
Cost capitalized subsequent to acquisition	692
Land	6,700
Buildings	25,570
Construction in progress	0
Total Purchase Price	32,270
Accumulated Depreciation	6,166
Book Value	26,104
Fixed rate mortgages	$ 15,290
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Cruse MarketPlace, Cumming, GA
Real Estate Properties [Line Items]
Initial Basis	$ 12,226
Cost capitalized subsequent to acquisition	688
Land	3,901
Buildings	9,013
Construction in progress	0
Total Purchase Price	12,914
Accumulated Depreciation	3,914
Book Value	9,000
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Flagship Center, Rockville, MD
Real Estate Properties [Line Items]
Initial Basis	$ 160
Cost capitalized subsequent to acquisition	9
Land	169
Buildings	0
Construction in progress	0
Total Purchase Price	169
Accumulated Depreciation	0
Book Value	169
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	0 years
Shopping Centers | French Market, Oklahoma City, OK
Real Estate Properties [Line Items]
Initial Basis	$ 5,781
Cost capitalized subsequent to acquisition	15,984
Land	1,118
Buildings	20,647
Construction in progress	0
Total Purchase Price	21,765
Accumulated Depreciation	13,133
Book Value	8,632
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Germantown, Germantown, MD
Real Estate Properties [Line Items]
Initial Basis	$ 2,034
Cost capitalized subsequent to acquisition	566
Land	2,034
Buildings	566
Construction in progress	0
Total Purchase Price	2,600
Accumulated Depreciation	455
Book Value	2,145
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | The Glen, Woodbridge, VA
Real Estate Properties [Line Items]
Initial Basis	$ 12,918
Cost capitalized subsequent to acquisition	8,466
Land	5,300
Buildings	16,084
Construction in progress	0
Total Purchase Price	21,384
Accumulated Depreciation	10,659
Book Value	10,725
Fixed rate mortgages	$ 21,933
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Great Falls Center, Great Falls, VA
Real Estate Properties [Line Items]
Initial Basis	$ 41,750
Cost capitalized subsequent to acquisition	3,203
Land	14,766
Buildings	30,187
Construction in progress	0
Total Purchase Price	44,953
Accumulated Depreciation	10,378
Book Value	34,575
Fixed rate mortgages	$ 9,788
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Hampshire Langley, Takoma, MD
Real Estate Properties [Line Items]
Initial Basis	$ 3,159
Cost capitalized subsequent to acquisition	3,368
Land	1,892
Buildings	4,635
Construction in progress	0
Total Purchase Price	6,527
Accumulated Depreciation	4,008
Book Value	2,519
Fixed rate mortgages	$ 13,480
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Hunt Club Corners, Apopka, FL
Real Estate Properties [Line Items]
Initial Basis	$ 12,584
Cost capitalized subsequent to acquisition	4,519
Land	4,822
Buildings	12,281
Construction in progress	0
Total Purchase Price	17,103
Accumulated Depreciation	5,250
Book Value	11,853
Fixed rate mortgages	$ 5,109
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Jamestown Place, Altamonte Springs, FL
Real Estate Properties [Line Items]
Initial Basis	$ 14,055
Cost capitalized subsequent to acquisition	2,245
Land	4,455
Buildings	11,845
Construction in progress	0
Total Purchase Price	16,300
Accumulated Depreciation	4,694
Book Value	11,606
Fixed rate mortgages	$ 6,110
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Kentlands Square I, Gaithersburg, MD
Real Estate Properties [Line Items]
Initial Basis	$ 14,379
Cost capitalized subsequent to acquisition	2,996
Land	5,006
Buildings	12,369
Construction in progress	0
Total Purchase Price	17,375
Accumulated Depreciation	4,474
Book Value	12,901
Fixed rate mortgages	$ 22,012
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Kentlands Square II, Gaithersburg, MD
Real Estate Properties [Line Items]
Initial Basis	$ 76,723
Cost capitalized subsequent to acquisition	2,774
Land	23,133
Buildings	56,364
Construction in progress	0
Total Purchase Price	79,497
Accumulated Depreciation	15,220
Book Value	64,277
Fixed rate mortgages	$ 32,585
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Kentlands Place, Gaithersburg, MD
Real Estate Properties [Line Items]
Initial Basis	$ 1,425
Cost capitalized subsequent to acquisition	7,404
Land	1,425
Buildings	7,404
Construction in progress	0
Total Purchase Price	8,829
Accumulated Depreciation	4,479
Book Value	4,350
Fixed rate mortgages	$ 7,734
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Lansdowne Town Center, Leesburg, VA
Real Estate Properties [Line Items]
Initial Basis	$ 6,545
Cost capitalized subsequent to acquisition	43,227
Land	6,546
Buildings	43,220
Construction in progress	6
Total Purchase Price	49,772
Accumulated Depreciation	17,708
Book Value	32,064
Fixed rate mortgages	$ 29,657
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Leesburg Pike Plaza, Baileys Crossroads, VA
Real Estate Properties [Line Items]
Initial Basis	$ 2,418
Cost capitalized subsequent to acquisition	6,294
Land	1,132
Buildings	7,580
Construction in progress	0
Total Purchase Price	8,712
Accumulated Depreciation	6,266
Book Value	2,446
Fixed rate mortgages	$ 13,836
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Lumberton Plaza, Lumberton, NJ
Real Estate Properties [Line Items]
Initial Basis	$ 4,400
Cost capitalized subsequent to acquisition	11,612
Land	950
Buildings	15,041
Construction in progress	21
Total Purchase Price	16,012
Accumulated Depreciation	13,709
Book Value	2,303
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Metro Pike Center, Rockville, MD
Real Estate Properties [Line Items]
Initial Basis	$ 33,123
Cost capitalized subsequent to acquisition	4,832
Land	26,064
Buildings	7,944
Construction in progress	3,947
Total Purchase Price	37,955
Accumulated Depreciation	2,046
Book Value	35,909
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Shops at Monocacy, Frederick, MD
Real Estate Properties [Line Items]
Initial Basis	$ 9,541
Cost capitalized subsequent to acquisition	14,385
Land	9,260
Buildings	14,666
Construction in progress	0
Total Purchase Price	23,926
Accumulated Depreciation	6,643
Book Value	17,283
Fixed rate mortgages	$ 27,836
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Northrock, Warrenton, VA
Real Estate Properties [Line Items]
Initial Basis	$ 12,686
Cost capitalized subsequent to acquisition	15,428
Land	12,686
Buildings	15,422
Construction in progress	6
Total Purchase Price	28,114
Accumulated Depreciation	5,386
Book Value	22,728
Fixed rate mortgages	$ 13,626
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Olde Forte Village, Ft. Washington, MD
Real Estate Properties [Line Items]
Initial Basis	$ 15,933
Cost capitalized subsequent to acquisition	6,795
Land	5,409
Buildings	17,319
Construction in progress	0
Total Purchase Price	22,728
Accumulated Depreciation	8,646
Book Value	14,082
Fixed rate mortgages	$ 21,204
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Olney, Olney, MD
Real Estate Properties [Line Items]
Initial Basis	$ 4,963
Cost capitalized subsequent to acquisition	2,623
Land	3,079
Buildings	4,507
Construction in progress	0
Total Purchase Price	7,586
Accumulated Depreciation	3,487
Book Value	4,099
Fixed rate mortgages	$ 12,125
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Orchard Park, Dunwoody, GA
Real Estate Properties [Line Items]
Initial Basis	$ 19,377
Cost capitalized subsequent to acquisition	1,553
Land	7,751
Buildings	13,179
Construction in progress	0
Total Purchase Price	20,930
Accumulated Depreciation	4,457
Book Value	16,473
Fixed rate mortgages	$ 9,136
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Palm Springs Center, Altamonte Springs, FL
Real Estate Properties [Line Items]
Initial Basis	$ 18,365
Cost capitalized subsequent to acquisition	2,029
Land	5,739
Buildings	14,655
Construction in progress	0
Total Purchase Price	20,394
Accumulated Depreciation	6,088
Book Value	14,306
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Ravenwood, Baltimore, MD
Real Estate Properties [Line Items]
Initial Basis	$ 1,245
Cost capitalized subsequent to acquisition	4,256
Land	703
Buildings	4,798
Construction in progress	0
Total Purchase Price	5,501
Accumulated Depreciation	3,435
Book Value	2,066
Fixed rate mortgages	$ 13,095
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | 11503 Rockville Pike/5541 Nicholson Lane, Rockville, MD
Real Estate Properties [Line Items]
Initial Basis	$ 26,561
Cost capitalized subsequent to acquisition	24
Land	22,113
Buildings	4,472
Construction in progress	0
Total Purchase Price	26,585
Accumulated Depreciation	1,146
Book Value	25,439
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | 1500/1580/1582/1584 Rockville Pike, Rockville, MD
Real Estate Properties [Line Items]
Initial Basis	$ 51,149
Cost capitalized subsequent to acquisition	2,750
Land	43,863
Buildings	7,490
Construction in progress	2,546
Total Purchase Price	53,899
Accumulated Depreciation	6,677
Book Value	47,222
Fixed rate mortgages	0
Shopping Centers | Seabreeze Plaza, Palm Harbor, FL
Real Estate Properties [Line Items]
Initial Basis	24,526
Cost capitalized subsequent to acquisition	2,502
Land	8,665
Buildings	18,363
Construction in progress	0
Total Purchase Price	27,028
Accumulated Depreciation	7,323
Book Value	19,705
Fixed rate mortgages	$ 14,469
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Market Place at Sea Colony, Bethany Beach, DE
Real Estate Properties [Line Items]
Initial Basis	$ 2,920
Cost capitalized subsequent to acquisition	261
Land	1,147
Buildings	2,034
Construction in progress	0
Total Purchase Price	3,181
Accumulated Depreciation	674
Book Value	2,507
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Seven Corners, Falls Church, VA
Real Estate Properties [Line Items]
Initial Basis	$ 4,848
Cost capitalized subsequent to acquisition	45,770
Land	4,929
Buildings	45,689
Construction in progress	0
Total Purchase Price	50,618
Accumulated Depreciation	32,078
Book Value	18,540
Fixed rate mortgages	$ 58,607
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Severna Park Marketplace, Severna Park, MD
Real Estate Properties [Line Items]
Initial Basis	$ 63,254
Cost capitalized subsequent to acquisition	526
Land	12,700
Buildings	51,080
Construction in progress	0
Total Purchase Price	63,780
Accumulated Depreciation	11,856
Book Value	51,924
Fixed rate mortgages	$ 28,480
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Shops at Fairfax, Fairfax, VA
Real Estate Properties [Line Items]
Initial Basis	$ 2,708
Cost capitalized subsequent to acquisition	11,062
Land	992
Buildings	12,778
Construction in progress	0
Total Purchase Price	13,770
Accumulated Depreciation	8,939
Book Value	4,831
Fixed rate mortgages	$ 10,127
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | Smallwood Village Center, Waldorf, MD
Real Estate Properties [Line Items]
Initial Basis	$ 17,819
Cost capitalized subsequent to acquisition	8,345
Land	6,402
Buildings	19,762
Construction in progress	0
Total Purchase Price	26,164
Accumulated Depreciation	9,655
Book Value	16,509
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Southdale, Glen Burnie, MD
Real Estate Properties [Line Items]
Initial Basis	$ 18,895
Cost capitalized subsequent to acquisition	25,098
Land	15,254
Buildings	28,739
Construction in progress	0
Total Purchase Price	43,993
Accumulated Depreciation	23,105
Book Value	20,888
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Southside Plaza, Richmond, VA
Real Estate Properties [Line Items]
Initial Basis	$ 6,728
Cost capitalized subsequent to acquisition	11,381
Land	1,878
Buildings	16,231
Construction in progress	0
Total Purchase Price	18,109
Accumulated Depreciation	13,105
Book Value	5,004
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | South Dekalb Plaza, Atlanta, GA
Real Estate Properties [Line Items]
Initial Basis	$ 2,474
Cost capitalized subsequent to acquisition	4,563
Land	703
Buildings	6,334
Construction in progress	0
Total Purchase Price	7,037
Accumulated Depreciation	5,228
Book Value	1,809
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Thruway, Winston-Salem, NC
Real Estate Properties [Line Items]
Initial Basis	$ 7,848
Cost capitalized subsequent to acquisition	26,569
Land	7,693
Buildings	26,693
Construction in progress	31
Total Purchase Price	34,417
Accumulated Depreciation	19,638
Book Value	14,779
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Village Center, Centreville, VA
Real Estate Properties [Line Items]
Initial Basis	$ 16,502
Cost capitalized subsequent to acquisition	2,636
Land	7,851
Buildings	11,287
Construction in progress	0
Total Purchase Price	19,138
Accumulated Depreciation	7,761
Book Value	11,377
Fixed rate mortgages	$ 12,061
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Westview Village, Frederick, MD
Real Estate Properties [Line Items]
Initial Basis	$ 6,047
Cost capitalized subsequent to acquisition	25,265
Land	6,047
Buildings	25,265
Construction in progress	0
Total Purchase Price	31,312
Accumulated Depreciation	10,448
Book Value	20,864
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	50 years
Shopping Centers | White Oak, Silver Spring, MD
Real Estate Properties [Line Items]
Initial Basis	$ 6,277
Cost capitalized subsequent to acquisition	6,020
Land	4,649
Buildings	7,446
Construction in progress	202
Total Purchase Price	12,297
Accumulated Depreciation	6,307
Book Value	5,990
Fixed rate mortgages	$ 21,704
Buildings and Improvements Depreciable Lives in Years	40 years
Shopping Centers | Other Buildings / Improvements
Real Estate Properties [Line Items]
Cost capitalized subsequent to acquisition	$ 182
Buildings	182
Construction in progress	0
Total Purchase Price	182
Accumulated Depreciation	102
Book Value	80
Fixed rate mortgages	0
Mixed-Use Properties
Real Estate Properties [Line Items]
Initial Basis	96,034
Cost capitalized subsequent to acquisition	663,187
Land	80,521
Buildings	670,049
Construction in progress	8,651
Total Purchase Price	759,221
Accumulated Depreciation	199,788
Book Value	559,433
Fixed rate mortgages	387,837
Mixed-Use Properties | Avenel Business Park, Gaithersburg, MD
Real Estate Properties [Line Items]
Initial Basis	21,459
Cost capitalized subsequent to acquisition	33,526
Land	3,756
Buildings	51,229
Construction in progress	0
Total Purchase Price	54,985
Accumulated Depreciation	40,108
Book Value	14,877
Fixed rate mortgages	$ 25,224
Mixed-Use Properties | Avenel Business Park, Gaithersburg, MD | Minimum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	35 years
Mixed-Use Properties | Avenel Business Park, Gaithersburg, MD | Maximum
Real Estate Properties [Line Items]
Buildings and Improvements Depreciable Lives in Years	40 years
Mixed-Use Properties | Clarendon Center, Arlington, VA (1)
Real Estate Properties [Line Items]
Initial Basis	$ 12,753
Cost capitalized subsequent to acquisition	186,314
Land	16,287
Buildings	182,780
Construction in progress	0
Total Purchase Price	199,067
Accumulated Depreciation	51,725
Book Value	147,342
Fixed rate mortgages	$ 94,712
Buildings and Improvements Depreciable Lives in Years	50 years
Mixed-Use Properties | Park Van Ness, Washington, DC
Real Estate Properties [Line Items]
Initial Basis	$ 2,242
Cost capitalized subsequent to acquisition	91,715
Land	2,242
Buildings	91,715
Construction in progress	0
Total Purchase Price	93,957
Accumulated Depreciation	13,739
Book Value	80,218
Fixed rate mortgages	$ 66,420
Buildings and Improvements Depreciable Lives in Years	50 years
Mixed-Use Properties | 601 Pennsylvania Ave., Washington, DC
Real Estate Properties [Line Items]
Initial Basis	$ 5,479
Cost capitalized subsequent to acquisition	69,328
Land	5,667
Buildings	69,140
Construction in progress	0
Total Purchase Price	74,807
Accumulated Depreciation	59,413
Book Value	15,394
Fixed rate mortgages	$ 0
Buildings and Improvements Depreciable Lives in Years	35 years
Mixed-Use Properties | The Waycroft, Arlington, VA
Real Estate Properties [Line Items]
Initial Basis	$ 52,067
Cost capitalized subsequent to acquisition	225,226
Land	52,025
Buildings	216,617
Construction in progress	8,651
Total Purchase Price	277,293
Accumulated Depreciation	4,722
Book Value	272,571
Fixed rate mortgages	$ 146,083
Buildings and Improvements Depreciable Lives in Years	50 years
Mixed-Use Properties | Washington Square, Alexandria, VA
Real Estate Properties [Line Items]
Initial Basis	$ 2,034
Cost capitalized subsequent to acquisition	57,078
Land	544
Buildings	58,568
Construction in progress	0
Total Purchase Price	59,112
Accumulated Depreciation	30,081
Book Value	29,031
Fixed rate mortgages	$ 55,398
Buildings and Improvements Depreciable Lives in Years	50 years
Development Land
Real Estate Properties [Line Items]
Initial Basis	$ 47,021
Cost capitalized subsequent to acquisition	15,870
Land	9,263
Buildings	0
Construction in progress	53,628
Total Purchase Price	62,891
Accumulated Depreciation	0
Book Value	62,891
Development land, related debt	0
Development Land | Ashland Square Phase II, Manassas, VA
Real Estate Properties [Line Items]
Initial Basis	5,292
Cost capitalized subsequent to acquisition	4,642
Land	7,029
Buildings	0
Construction in progress	2,905
Total Purchase Price	9,934
Accumulated Depreciation	0
Book Value	9,934
Development land, related debt	$ 0
Buildings and Improvements Depreciable Lives in Years
Development Land | New Market, New Market, MD
Real Estate Properties [Line Items]
Initial Basis	$ 2,088
Cost capitalized subsequent to acquisition	146
Land	2,234
Buildings	0
Construction in progress	0
Total Purchase Price	2,234
Accumulated Depreciation	0
Book Value	2,234
Development land, related debt	$ 0
Buildings and Improvements Depreciable Lives in Years
Development Land | Hampden House (formerly 7316 Wisconsin Avenue), Bethesda, MD
Real Estate Properties [Line Items]
Initial Basis	$ 39,641
Cost capitalized subsequent to acquisition	11,082
Land
Buildings	0
Construction in progress	50,723
Total Purchase Price	50,723
Accumulated Depreciation	0
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