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Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | $ 315,437 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 443,949 |  |  |
Buildings and Improvements | 2,886,455 |  |  |
Net Improvements (Retirements) Since Acquisition | 676,055 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 489,702 |  |  |
Buildings and Improvements | 3,516,757 |  |  |
Total | 4,006,459 | $ 3,951,719 | $ 3,830,824 | $ 3,658,438
Accumulated Depreciation at December 31, 2019 | 973,318 | 885,407 | $ 913,297 | $ 885,392
Pennsylvania | 400 Berwyn Park |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,657 |  |
Buildings and Improvements |  | 4,462 |  |
Net Improvements (Retirements) Since Acquisition |  | 12,841 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,657 |  |
Buildings and Improvements |  | 17,303 |  |
Total |  | 19,960 |  |
Accumulated Depreciation at December 31, 2019 |  | 7,583 |  |
Pennsylvania | 300 Berwyn Park |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,206 |  |
Buildings and Improvements |  | 13,422 |  |
Net Improvements (Retirements) Since Acquisition |  | 4,145 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,206 |  |
Buildings and Improvements |  | 17,567 |  |
Total |  | 19,773 |  |
Accumulated Depreciation at December 31, 2019 |  | 10,516 |  |
Pennsylvania | 1050 Westlakes Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,611 |  |
Buildings and Improvements |  | 10,445 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,210 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,611 |  |
Buildings and Improvements |  | 12,655 |  |
Total |  | 15,266 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,238 |  |
Pennsylvania | 1200 Swedesford Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,595 |  |
Buildings and Improvements |  | 11,809 |  |
Net Improvements (Retirements) Since Acquisition |  | 490 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,595 |  |
Buildings and Improvements |  | 12,299 |  |
Total |  | 14,894 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,848 |  |
Pennsylvania | 200 Berwyn Park |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,533 |  |
Buildings and Improvements |  | 9,460 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,574 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,533 |  |
Buildings and Improvements |  | 11,034 |  |
Total |  | 12,567 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,569 |  |
Pennsylvania | 1180 Swedesford Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,086 |  |
Buildings and Improvements |  | 8,342 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,865 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,086 |  |
Buildings and Improvements |  | 11,207 |  |
Total |  | 13,293 |  |
Accumulated Depreciation at December 31, 2019 |  | 5,802 |  |
Pennsylvania | 100 Berwyn Park |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,180 |  |
Buildings and Improvements |  | 7,290 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,419 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,180 |  |
Buildings and Improvements |  | 8,709 |  |
Total |  | 9,889 |  |
Accumulated Depreciation at December 31, 2019 |  | 5,252 |  |
Pennsylvania | 1160 Swedesford Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,781 |  |
Buildings and Improvements |  | 7,124 |  |
Net Improvements (Retirements) Since Acquisition |  | 6,810 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,045 |  |
Buildings and Improvements |  | 13,670 |  |
Total |  | 15,715 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,698 |  |
Pennsylvania | 1100 Cassett Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,695 |  |
Buildings and Improvements |  | 6,779 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,730 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,695 |  |
Buildings and Improvements |  | 8,509 |  |
Total |  | 10,204 |  |
Accumulated Depreciation at December 31, 2019 |  | 4,044 |  |
Pennsylvania | Six Tower Bridge (181 Washington Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 6,927 |  |
Buildings and Improvements |  | 14,722 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,511 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 6,237 |  |
Buildings and Improvements |  | 17,923 |  |
Total |  | 24,160 |  |
Accumulated Depreciation at December 31, 2019 |  | 3,803 |  |
Pennsylvania | 52 Swedesford Square |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 4,241 |  |
Buildings and Improvements |  | 16,579 |  |
Net Improvements (Retirements) Since Acquisition |  | 5,193 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 4,241 |  |
Buildings and Improvements |  | 21,772 |  |
Total |  | 26,013 |  |
Accumulated Depreciation at December 31, 2019 |  | 11,511 |  |
Pennsylvania | 640 Freedom Business Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,015 |  |
Buildings and Improvements |  | 20,098 |  |
Net Improvements (Retirements) Since Acquisition |  | 4,832 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 414 |  |
Buildings and Improvements |  | 25,531 |  |
Total |  | 25,945 |  |
Accumulated Depreciation at December 31, 2019 |  | 14,251 |  |
Pennsylvania | 620 Freedom Business Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 666 |  |
Buildings and Improvements |  | 13,118 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,826 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 270 |  |
Buildings and Improvements |  | 15,340 |  |
Total |  | 15,610 |  |
Accumulated Depreciation at December 31, 2019 |  | 8,836 |  |
Pennsylvania | 1000 First Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 13,708 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,211 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 16,919 |  |
Total |  | 16,919 |  |
Accumulated Depreciation at December 31, 2019 |  | 10,766 |  |
Pennsylvania | 1060 First Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 13,665 |  |
Net Improvements (Retirements) Since Acquisition |  | 4,169 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 17,834 |  |
Total |  | 17,834 |  |
Accumulated Depreciation at December 31, 2019 |  | 11,055 |  |
Pennsylvania | 630 Freedom Business Center Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 666 |  |
Buildings and Improvements |  | 13,251 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,259 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 273 |  |
Buildings and Improvements |  | 16,903 |  |
Total |  | 17,176 |  |
Accumulated Depreciation at December 31, 2019 |  | 9,861 |  |
Pennsylvania | 1020 First Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 10,744 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,931 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 14,675 |  |
Total |  | 14,675 |  |
Accumulated Depreciation at December 31, 2019 |  | 9,089 |  |
Pennsylvania | 1040 First Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 14,142 |  |
Net Improvements (Retirements) Since Acquisition |  | 5,080 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 0 |  |
Buildings and Improvements |  | 19,222 |  |
Total |  | 19,222 |  |
Accumulated Depreciation at December 31, 2019 |  | 12,076 |  |
Pennsylvania | 610 Freedom Business Center Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 485 |  |
Buildings and Improvements |  | 9,602 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,676 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 198 |  |
Buildings and Improvements |  | 12,565 |  |
Total |  | 12,763 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,976 |  |
Pennsylvania | 650 Park Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,916 |  |
Buildings and Improvements |  | 4,378 |  |
Net Improvements (Retirements) Since Acquisition |  | (4,378) |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,916 |  |
Buildings and Improvements |  | 0 |  |
Total |  | 1,916 |  |
Accumulated Depreciation at December 31, 2019 |  | 0 |  |
Pennsylvania | 600 Park Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,012 |  |
Buildings and Improvements |  | 4,048 |  |
Net Improvements (Retirements) Since Acquisition |  | 385 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,012 |  |
Buildings and Improvements |  | 4,433 |  |
Total |  | 5,445 |  |
Accumulated Depreciation at December 31, 2019 |  | 2,647 |  |
Pennsylvania | 933 First Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,127 |  |
Buildings and Improvements |  | 20,794 |  |
Net Improvements (Retirements) Since Acquisition |  | (1,125) |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,127 |  |
Buildings and Improvements |  | 19,669 |  |
Total |  | 22,796 |  |
Accumulated Depreciation at December 31, 2019 |  | 2,216 |  |
Pennsylvania | 500 North Gulph Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,303 |  |
Buildings and Improvements |  | 5,201 |  |
Net Improvements (Retirements) Since Acquisition |  | 21,017 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,303 |  |
Buildings and Improvements |  | 26,218 |  |
Total |  | 27,521 |  |
Accumulated Depreciation at December 31, 2019 |  | 1,202 |  |
Pennsylvania | 401 Plymouth Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 6,199 |  |
Buildings and Improvements |  | 16,131 |  |
Net Improvements (Retirements) Since Acquisition |  | 15,831 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 6,199 |  |
Buildings and Improvements |  | 31,962 |  |
Total |  | 38,161 |  |
Accumulated Depreciation at December 31, 2019 |  | 15,355 |  |
Pennsylvania | Metroplex (4000 Chemical Road) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 4,373 |  |
Buildings and Improvements |  | 24,546 |  |
Net Improvements (Retirements) Since Acquisition |  | 399 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 4,373 |  |
Buildings and Improvements |  | 24,945 |  |
Total |  | 29,318 |  |
Accumulated Depreciation at December 31, 2019 |  | 7,701 |  |
Pennsylvania | 610 West Germantown Pike |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,651 |  |
Buildings and Improvements |  | 14,514 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,285 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,651 |  |
Buildings and Improvements |  | 17,799 |  |
Total |  | 21,450 |  |
Accumulated Depreciation at December 31, 2019 |  | 8,669 |  |
Pennsylvania | 600 West Germantown Pike |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,652 |  |
Buildings and Improvements |  | 15,288 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,717 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,652 |  |
Buildings and Improvements |  | 18,005 |  |
Total |  | 21,657 |  |
Accumulated Depreciation at December 31, 2019 |  | 8,124 |  |
Pennsylvania | 630 West Germantown Pike |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,558 |  |
Buildings and Improvements |  | 14,743 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,714 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,558 |  |
Buildings and Improvements |  | 17,457 |  |
Total |  | 21,015 |  |
Accumulated Depreciation at December 31, 2019 |  | 7,906 |  |
Pennsylvania | 620 West Germantown Pike |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,572 |  |
Buildings and Improvements |  | 14,435 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,498 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,572 |  |
Buildings and Improvements |  | 15,933 |  |
Total |  | 19,505 |  |
Accumulated Depreciation at December 31, 2019 |  | 7,042 |  |
Pennsylvania | 660 West Germantown Pike |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,694 |  |
Buildings and Improvements |  | 5,487 |  |
Net Improvements (Retirements) Since Acquisition |  | 20,715 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 5,405 |  |
Buildings and Improvements |  | 24,491 |  |
Total |  | 29,896 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,850 |  |
Pennsylvania | 351 Plymouth Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 1,043 |  |
Buildings and Improvements |  | 555 |  |
Net Improvements (Retirements) Since Acquisition |  | 0 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 1,043 |  |
Buildings and Improvements |  | 555 |  |
Total |  | 1,598 |  |
Accumulated Depreciation at December 31, 2019 |  | 205 |  |
Pennsylvania | 150 Radnor Chester Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 11,925 |  |
Buildings and Improvements |  | 36,986 |  |
Net Improvements (Retirements) Since Acquisition |  | 10,142 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 11,897 |  |
Buildings and Improvements |  | 47,156 |  |
Total |  | 59,053 |  |
Accumulated Depreciation at December 31, 2019 |  | 22,504 |  |
Pennsylvania | One Radnor Corporate Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 7,323 |  |
Buildings and Improvements |  | 28,613 |  |
Net Improvements (Retirements) Since Acquisition |  | 22,885 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 7,323 |  |
Buildings and Improvements |  | 51,498 |  |
Total |  | 58,821 |  |
Accumulated Depreciation at December 31, 2019 |  | 30,974 |  |
Pennsylvania | 201 King of Prussia Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 8,956 |  |
Buildings and Improvements |  | 29,811 |  |
Net Improvements (Retirements) Since Acquisition |  | 2,871 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 8,949 |  |
Buildings and Improvements |  | 32,689 |  |
Total |  | 41,638 |  |
Accumulated Depreciation at December 31, 2019 |  | 19,061 |  |
Pennsylvania | 555 Lancaster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 8,014 |  |
Buildings and Improvements |  | 16,508 |  |
Net Improvements (Retirements) Since Acquisition |  | 20,204 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 8,609 |  |
Buildings and Improvements |  | 36,117 |  |
Total |  | 44,726 |  |
Accumulated Depreciation at December 31, 2019 |  | 18,535 |  |
Pennsylvania | Four Radnor Corporate Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 5,406 |  |
Buildings and Improvements |  | 21,390 |  |
Net Improvements (Retirements) Since Acquisition |  | 12,770 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 5,705 |  |
Buildings and Improvements |  | 33,861 |  |
Total |  | 39,566 |  |
Accumulated Depreciation at December 31, 2019 |  | 15,781 |  |
Pennsylvania | Five Radnor Corporate Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 6,506 |  |
Buildings and Improvements |  | 25,525 |  |
Net Improvements (Retirements) Since Acquisition |  | 8,209 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 6,578 |  |
Buildings and Improvements |  | 33,662 |  |
Total |  | 40,240 |  |
Accumulated Depreciation at December 31, 2019 |  | 12,120 |  |
Pennsylvania | Three Radnor Corporate Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 4,773 |  |
Buildings and Improvements |  | 17,961 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,273 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 4,791 |  |
Buildings and Improvements |  | 19,216 |  |
Total |  | 24,007 |  |
Accumulated Depreciation at December 31, 2019 |  | 9,598 |  |
Pennsylvania | Two Radnor Corporate Center |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,937 |  |
Buildings and Improvements |  | 15,484 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,163 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,942 |  |
Buildings and Improvements |  | 18,642 |  |
Total |  | 22,584 |  |
Accumulated Depreciation at December 31, 2019 |  | 9,853 |  |
Pennsylvania | 130 Radnor Chester Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,573 |  |
Buildings and Improvements |  | 8,338 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,188 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,567 |  |
Buildings and Improvements |  | 11,532 |  |
Total |  | 14,099 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,716 |  |
Pennsylvania | 170 Radnor Chester Road |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 2,514 |  |
Buildings and Improvements |  | 8,147 |  |
Net Improvements (Retirements) Since Acquisition |  | 1,751 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 2,509 |  |
Buildings and Improvements |  | 9,903 |  |
Total |  | 12,412 |  |
Accumulated Depreciation at December 31, 2019 |  | 4,375 |  |
Pennsylvania | 200 N. Radnor Chester Rd. |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,366 |  |
Buildings and Improvements |  | 0 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,653 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,366 |  |
Buildings and Improvements |  | 3,653 |  |
Total |  | 7,019 |  |
Accumulated Depreciation at December 31, 2019 |  | 772 |  |
Pennsylvania | 101 West Elm Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 6,251 |  |
Buildings and Improvements |  | 25,209 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,853 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 6,251 |  |
Buildings and Improvements |  | 29,062 |  |
Total |  | 35,313 |  |
Accumulated Depreciation at December 31, 2019 |  | 10,721 |  |
Pennsylvania | 1 West Elm Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 0 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 3,557 |  |
Buildings and Improvements |  | 14,249 |  |
Net Improvements (Retirements) Since Acquisition |  | 3,376 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 3,557 |  |
Buildings and Improvements |  | 17,625 |  |
Total |  | 21,182 |  |
Accumulated Depreciation at December 31, 2019 |  | 6,823 |  |
Pennsylvania | Four Tower Bridge (200 Barr Harbor Drive) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances |  | 9,291 |  |
Initial Cost [Abstract] |  |  |  |
Land |  | 6,000 |  |
Buildings and Improvements |  | 14,734 |  |
Net Improvements (Retirements) Since Acquisition |  | 336 |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land |  | 6,000 |  |
Buildings and Improvements |  | 15,070 |  |
Total |  | 21,070 |  |
Accumulated Depreciation at December 31, 2019 |  | $ 761 |  |
Philadelphia CBD | Cira Centre (2929 Arch Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 208,570 |  |  |
Net Improvements (Retirements) Since Acquisition | (17,837) |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 12,586 |  |  |
Buildings and Improvements | 178,147 |  |  |
Total | 190,733 |  |  |
Accumulated Depreciation at December 31, 2019 | 62,966 |  |  |
Philadelphia CBD | Three Logan Square (1717 Arch Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 98,188 |  |  |
Net Improvements (Retirements) Since Acquisition | 75,116 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 25,195 |  |  |
Buildings and Improvements | 148,109 |  |  |
Total | 173,304 |  |  |
Accumulated Depreciation at December 31, 2019 | 40,161 |  |  |
Philadelphia CBD | Two Commerce Square (2001 Market Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 108,472 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 15,323 |  |  |
Buildings and Improvements | 120,200 |  |  |
Net Improvements (Retirements) Since Acquisition | 33,693 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 15,323 |  |  |
Buildings and Improvements | 153,893 |  |  |
Total | 169,216 |  |  |
Accumulated Depreciation at December 31, 2019 | 27,952 |  |  |
Philadelphia CBD | One Logan Square (130 North 18th Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 14,496 |  |  |
Buildings and Improvements | 107,736 |  |  |
Net Improvements (Retirements) Since Acquisition | 30,019 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 14,473 |  |  |
Buildings and Improvements | 137,778 |  |  |
Total | 152,251 |  |  |
Accumulated Depreciation at December 31, 2019 | 62,425 |  |  |
Philadelphia CBD | Two Logan Square (100 North 18th Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 81,103 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 16,066 |  |  |
Buildings and Improvements | 100,255 |  |  |
Net Improvements (Retirements) Since Acquisition | 20,061 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 16,066 |  |  |
Buildings and Improvements | 120,316 |  |  |
Total | 136,382 |  |  |
Accumulated Depreciation at December 31, 2019 | 49,266 |  |  |
Philadelphia CBD | One Commerce Square (2005 Market Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 116,571 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 15,161 |  |  |
Buildings and Improvements | 105,021 |  |  |
Net Improvements (Retirements) Since Acquisition | 32,326 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 15,160 |  |  |
Buildings and Improvements | 137,348 |  |  |
Total | 152,508 |  |  |
Accumulated Depreciation at December 31, 2019 | 25,304 |  |  |
Philadelphia CBD | Cira Centre South Garage (129 South 30th Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 76,008 |  |  |
Net Improvements (Retirements) Since Acquisition | 26,832 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 6,905 |  |  |
Buildings and Improvements | 95,935 |  |  |
Total | 102,840 |  |  |
Accumulated Depreciation at December 31, 2019 | 19,682 |  |  |
Philadelphia CBD | 1900 Market Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 7,768 |  |  |
Buildings and Improvements | 17,263 |  |  |
Net Improvements (Retirements) Since Acquisition | 63,292 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 7,768 |  |  |
Buildings and Improvements | 80,555 |  |  |
Total | 88,323 |  |  |
Accumulated Depreciation at December 31, 2019 | 15,492 |  |  |
Philadelphia CBD | 3020 Market Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 21,417 |  |  |
Net Improvements (Retirements) Since Acquisition | 8,272 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 29,689 |  |  |
Total | 29,689 |  |  |
Accumulated Depreciation at December 31, 2019 | 10,492 |  |  |
Philadelphia CBD | 618-634 Market Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 13,365 |  |  |
Buildings and Improvements | 5,791 |  |  |
Net Improvements (Retirements) Since Acquisition | 2,176 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 13,365 |  |  |
Buildings and Improvements | 7,967 |  |  |
Total | 21,332 |  |  |
Accumulated Depreciation at December 31, 2019 | 5,975 |  |  |
Philadelphia CBD | FMC Tower at Cira Centre South (2929 Walnut Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 400,294 |  |  |
Net Improvements (Retirements) Since Acquisition | 13,296 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 413,590 |  |  |
Total | 413,590 |  |  |
Accumulated Depreciation at December 31, 2019 | 47,285 |  |  |
Philadelphia CBD | 2100 Market Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 18,827 |  |  |
Buildings and Improvements | 0 |  |  |
Net Improvements (Retirements) Since Acquisition | 6,433 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 18,854 |  |  |
Buildings and Improvements | 6,406 |  |  |
Total | 25,260 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,027 |  |  |
Philadelphia CBD | 3000 Market Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 18,924 |  |  |
Buildings and Improvements | 13,080 |  |  |
Net Improvements (Retirements) Since Acquisition | 1,039 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 18,924 |  |  |
Buildings and Improvements | 14,119 |  |  |
Total | 33,043 |  |  |
Accumulated Depreciation at December 31, 2019 | 2,979 |  |  |
Philadelphia CBD | The Bulletin Building (3025 Market Street) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 24,377 |  |  |
Net Improvements (Retirements) Since Acquisition | 13,353 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 37,730 |  |  |
Total | 37,730 |  |  |
Accumulated Depreciation at December 31, 2019 | 2,086 |  |  |
Philadelphia CBD | 3001-3003 JFK Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 0 |  |  |
Net Improvements (Retirements) Since Acquisition | 111 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 111 |  |  |
Total | 111 |  |  |
Accumulated Depreciation at December 31, 2019 | 10 |  |  |
Philadelphia CBD | 3025 JFK Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 0 |  |  |
Net Improvements (Retirements) Since Acquisition | 0 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 0 |  |  |
Total | 0 |  |  |
Accumulated Depreciation at December 31, 2019 | 0 |  |  |
Metropolitan DC | 6600 Rockledge Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 37,421 |  |  |
Net Improvements (Retirements) Since Acquisition | 9,270 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 46,691 |  |  |
Total | 46,691 |  |  |
Accumulated Depreciation at December 31, 2019 | 14,871 |  |  |
Metropolitan DC | 2340 Dulles Corner Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 16,345 |  |  |
Buildings and Improvements | 65,379 |  |  |
Net Improvements (Retirements) Since Acquisition | 524 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 16,129 |  |  |
Buildings and Improvements | 66,119 |  |  |
Total | 82,248 |  |  |
Accumulated Depreciation at December 31, 2019 | 22,150 |  |  |
Metropolitan DC | 1676 International Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 18,437 |  |  |
Buildings and Improvements | 97,538 |  |  |
Net Improvements (Retirements) Since Acquisition | (962) |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 18,785 |  |  |
Buildings and Improvements | 96,228 |  |  |
Total | 115,013 |  |  |
Accumulated Depreciation at December 31, 2019 | 25,451 |  |  |
Metropolitan DC | 8260 Greensboro Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 7,952 |  |  |
Buildings and Improvements | 33,964 |  |  |
Net Improvements (Retirements) Since Acquisition | 4,955 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 8,102 |  |  |
Buildings and Improvements | 38,769 |  |  |
Total | 46,871 |  |  |
Accumulated Depreciation at December 31, 2019 | 11,152 |  |  |
Metropolitan DC | 2273 Research Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 5,167 |  |  |
Buildings and Improvements | 31,110 |  |  |
Net Improvements (Retirements) Since Acquisition | 5,799 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 5,237 |  |  |
Buildings and Improvements | 36,839 |  |  |
Total | 42,076 |  |  |
Accumulated Depreciation at December 31, 2019 | 11,928 |  |  |
Metropolitan DC | 2275 Research Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 5,059 |  |  |
Buildings and Improvements | 29,668 |  |  |
Net Improvements (Retirements) Since Acquisition | 7,588 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 5,154 |  |  |
Buildings and Improvements | 37,161 |  |  |
Total | 42,315 |  |  |
Accumulated Depreciation at December 31, 2019 | 13,308 |  |  |
Metropolitan DC | 2277 Research Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 4,649 |  |  |
Buildings and Improvements | 26,952 |  |  |
Net Improvements (Retirements) Since Acquisition | 18,853 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 4,733 |  |  |
Buildings and Improvements | 45,721 |  |  |
Total | 50,454 |  |  |
Accumulated Depreciation at December 31, 2019 | 17,093 |  |  |
Metropolitan DC | 8521 Leesburg Pike |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 4,316 |  |  |
Buildings and Improvements | 30,885 |  |  |
Net Improvements (Retirements) Since Acquisition | 7,145 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 4,397 |  |  |
Buildings and Improvements | 37,949 |  |  |
Total | 42,346 |  |  |
Accumulated Depreciation at December 31, 2019 | 11,925 |  |  |
Austin, Texas | 11501 Burnet Road - Building 1 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 3,755 |  |  |
Buildings and Improvements | 22,702 |  |  |
Net Improvements (Retirements) Since Acquisition | 115 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 3,755 |  |  |
Buildings and Improvements | 22,817 |  |  |
Total | 26,572 |  |  |
Accumulated Depreciation at December 31, 2019 | 3,193 |  |  |
Austin, Texas | 11501 Burnet Road - Building 2 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 2,732 |  |  |
Buildings and Improvements | 16,305 |  |  |
Net Improvements (Retirements) Since Acquisition | 1,551 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 2,732 |  |  |
Buildings and Improvements | 17,856 |  |  |
Total | 20,588 |  |  |
Accumulated Depreciation at December 31, 2019 | 2,920 |  |  |
Austin, Texas | 11501 Burnet Road - Building 3 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 3,688 |  |  |
Buildings and Improvements | 22,348 |  |  |
Net Improvements (Retirements) Since Acquisition | 94 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 3,688 |  |  |
Buildings and Improvements | 22,442 |  |  |
Total | 26,130 |  |  |
Accumulated Depreciation at December 31, 2019 | 3,161 |  |  |
Austin, Texas | 11501 Burnet Road - Building 4 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 2,614 |  |  |
Buildings and Improvements | 15,740 |  |  |
Net Improvements (Retirements) Since Acquisition | 75 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 2,614 |  |  |
Buildings and Improvements | 15,815 |  |  |
Total | 18,429 |  |  |
Accumulated Depreciation at December 31, 2019 | 2,242 |  |  |
Austin, Texas | 11501 Burnet Road - Building 5 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 3,689 |  |  |
Buildings and Improvements | 22,354 |  |  |
Net Improvements (Retirements) Since Acquisition | 118 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 3,689 |  |  |
Buildings and Improvements | 22,472 |  |  |
Total | 26,161 |  |  |
Accumulated Depreciation at December 31, 2019 | 3,207 |  |  |
Austin, Texas | 11501 Burnet Road - Building 6 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 2,676 |  |  |
Buildings and Improvements | 15,972 |  |  |
Net Improvements (Retirements) Since Acquisition | 13,973 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 2,676 |  |  |
Buildings and Improvements | 29,945 |  |  |
Total | 32,621 |  |  |
Accumulated Depreciation at December 31, 2019 | 3,408 |  |  |
Austin, Texas | 11501 Burnet Road - Building 8 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 1,400 |  |  |
Buildings and Improvements | 7,422 |  |  |
Net Improvements (Retirements) Since Acquisition | 1,547 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 1,400 |  |  |
Buildings and Improvements | 8,969 |  |  |
Total | 10,369 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,172 |  |  |
Austin, Texas | 11501 Burnet Road - Parking Garage |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 19,826 |  |  |
Net Improvements (Retirements) Since Acquisition | 63 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 0 |  |  |
Buildings and Improvements | 19,889 |  |  |
Total | 19,889 |  |  |
Accumulated Depreciation at December 31, 2019 | 3,628 |  |  |
Austin, Texas | Four Points Centre 3, 11120 Four Points Drive |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 1,140 |  |  |
Buildings and Improvements | 0 |  |  |
Net Improvements (Retirements) Since Acquisition | 40,564 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 1,140 |  |  |
Buildings and Improvements | 40,564 |  |  |
Total | 41,704 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,511 |  |  |
Austin, Texas | One Barton Skyway (1501 South MoPac Expressway) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 10,496 |  |  |
Buildings and Improvements | 47,670 |  |  |
Net Improvements (Retirements) Since Acquisition | 113 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 10,495 |  |  |
Buildings and Improvements | 47,784 |  |  |
Total | 58,279 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,378 |  |  |
Austin, Texas | Two Barton Skyway (1601 South MoPac Expressway) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 10,849 |  |  |
Buildings and Improvements | 53,868 |  |  |
Net Improvements (Retirements) Since Acquisition | 2,828 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 10,848 |  |  |
Buildings and Improvements | 56,697 |  |  |
Total | 67,545 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,810 |  |  |
Austin, Texas | Three Barton Skyway (1221 South MoPac Expressway) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 10,374 |  |  |
Buildings and Improvements | 47,624 |  |  |
Net Improvements (Retirements) Since Acquisition | 184 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 10,373 |  |  |
Buildings and Improvements | 47,809 |  |  |
Total | 58,182 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,343 |  |  |
Austin, Texas | Four Barton Skyway (1301 South MoPac Expressway) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 13,301 |  |  |
Buildings and Improvements | 57,041 |  |  |
Net Improvements (Retirements) Since Acquisition | (40) |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 13,300 |  |  |
Buildings and Improvements | 57,002 |  |  |
Total | 70,302 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,583 |  |  |
Austin, Texas | Four Points Centre (11305 Four Points Drive) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 7,800 |  |  |
Buildings and Improvements | 43,581 |  |  |
Net Improvements (Retirements) Since Acquisition | 3,463 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 7,800 |  |  |
Buildings and Improvements | 47,044 |  |  |
Total | 54,844 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,427 |  |  |
Austin, Texas | River Place - Building 1 (6500 River Place Boulevard) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 2,004 |  |  |
Buildings and Improvements | 17,680 |  |  |
Net Improvements (Retirements) Since Acquisition | 476 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 2,004 |  |  |
Buildings and Improvements | 18,156 |  |  |
Total | 20,160 |  |  |
Accumulated Depreciation at December 31, 2019 | 547 |  |  |
Austin, Texas | River Place - Building 2 (6500 River Place Boulevard) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 3,137 |  |  |
Buildings and Improvements | 29,254 |  |  |
Net Improvements (Retirements) Since Acquisition | 191 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 3,137 |  |  |
Buildings and Improvements | 29,445 |  |  |
Total | 32,582 |  |  |
Accumulated Depreciation at December 31, 2019 | 816 |  |  |
Austin, Texas | River Place - Building 3 (6500 River Place Boulevard) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 3,064 |  |  |
Buildings and Improvements | 26,705 |  |  |
Net Improvements (Retirements) Since Acquisition | 12 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 3,064 |  |  |
Buildings and Improvements | 26,717 |  |  |
Total | 29,781 |  |  |
Accumulated Depreciation at December 31, 2019 | 735 |  |  |
Austin, Texas | River Place - Building 4 (6500 River Place Boulevard |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 2,273 |  |  |
Buildings and Improvements | 18,617 |  |  |
Net Improvements (Retirements) Since Acquisition | 1,001 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 2,273 |  |  |
Buildings and Improvements | 19,618 |  |  |
Total | 21,891 |  |  |
Accumulated Depreciation at December 31, 2019 | 674 |  |  |
Austin, Texas | River Place - Building 5 (6500 River Place Boulevard) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 1,752 |  |  |
Buildings and Improvements | 14,315 |  |  |
Net Improvements (Retirements) Since Acquisition | (24) |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 1,752 |  |  |
Buildings and Improvements | 14,291 |  |  |
Total | 16,043 |  |  |
Accumulated Depreciation at December 31, 2019 | 394 |  |  |
Austin, Texas | River Place - Building 6 (6500 River Place Boulevard) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 1,598 |  |  |
Buildings and Improvements | 12,945 |  |  |
Net Improvements (Retirements) Since Acquisition | (24) |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 1,598 |  |  |
Buildings and Improvements | 12,921 |  |  |
Total | 14,519 |  |  |
Accumulated Depreciation at December 31, 2019 | 356 |  |  |
Austin, Texas | River Place - Building 7 (6500 River Place Boulevard) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 1,801 |  |  |
Buildings and Improvements | 16,486 |  |  |
Net Improvements (Retirements) Since Acquisition | 1,051 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 1,801 |  |  |
Buildings and Improvements | 17,537 |  |  |
Total | 19,338 |  |  |
Accumulated Depreciation at December 31, 2019 | 586 |  |  |
Austin, Texas | Quarry Lake II (4516 Seton Center Parkway) |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 3,970 |  |  |
Buildings and Improvements | 30,546 |  |  |
Net Improvements (Retirements) Since Acquisition | 821 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 3,867 |  |  |
Buildings and Improvements | 31,470 |  |  |
Total | 35,337 |  |  |
Accumulated Depreciation at December 31, 2019 | 876 |  |  |
Other | 10 Foster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 244 |  |  |
Buildings and Improvements | 971 |  |  |
Net Improvements (Retirements) Since Acquisition | 69 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 244 |  |  |
Buildings and Improvements | 1,040 |  |  |
Total | 1,284 |  |  |
Accumulated Depreciation at December 31, 2019 | 624 |  |  |
Other | 7 Foster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 231 |  |  |
Buildings and Improvements | 921 |  |  |
Net Improvements (Retirements) Since Acquisition | 31 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 231 |  |  |
Buildings and Improvements | 952 |  |  |
Total | 1,183 |  |  |
Accumulated Depreciation at December 31, 2019 | 549 |  |  |
Other | 2 Foster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 185 |  |  |
Buildings and Improvements | 730 |  |  |
Net Improvements (Retirements) Since Acquisition | 11 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 185 |  |  |
Buildings and Improvements | 741 |  |  |
Total | 926 |  |  |
Accumulated Depreciation at December 31, 2019 | 741 |  |  |
Other | 4 Foster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 183 |  |  |
Buildings and Improvements | 726 |  |  |
Net Improvements (Retirements) Since Acquisition | 6 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 183 |  |  |
Buildings and Improvements | 732 |  |  |
Total | 915 |  |  |
Accumulated Depreciation at December 31, 2019 | 732 |  |  |
Other | 1 Foster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 93 |  |  |
Buildings and Improvements | 364 |  |  |
Net Improvements (Retirements) Since Acquisition | 8 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 93 |  |  |
Buildings and Improvements | 372 |  |  |
Total | 465 |  |  |
Accumulated Depreciation at December 31, 2019 | 372 |  |  |
Other | 5 U.S. Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 21 |  |  |
Buildings and Improvements | 81 |  |  |
Net Improvements (Retirements) Since Acquisition | 2 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 21 |  |  |
Buildings and Improvements | 83 |  |  |
Total | 104 |  |  |
Accumulated Depreciation at December 31, 2019 | 83 |  |  |
Other | 5 Foster Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 9 |  |  |
Buildings and Improvements | 32 |  |  |
Net Improvements (Retirements) Since Acquisition | 3 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 9 |  |  |
Buildings and Improvements | 35 |  |  |
Total | 44 |  |  |
Accumulated Depreciation at December 31, 2019 | 35 |  |  |
Other | Main Street-Plaza 1000 |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 2,732 |  |  |
Buildings and Improvements | 10,942 |  |  |
Net Improvements (Retirements) Since Acquisition | 296 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 2,732 |  |  |
Buildings and Improvements | 11,238 |  |  |
Total | 13,970 |  |  |
Accumulated Depreciation at December 31, 2019 | 11,008 |  |  |
Other | Main Street-Piazza |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 696 |  |  |
Buildings and Improvements | 2,802 |  |  |
Net Improvements (Retirements) Since Acquisition | 3,700 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 704 |  |  |
Buildings and Improvements | 6,494 |  |  |
Total | 7,198 |  |  |
Accumulated Depreciation at December 31, 2019 | 3,515 |  |  |
Other | Main Street-Promenade |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 532 |  |  |
Buildings and Improvements | 2,052 |  |  |
Net Improvements (Retirements) Since Acquisition | 312 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 532 |  |  |
Buildings and Improvements | 2,364 |  |  |
Total | 2,896 |  |  |
Accumulated Depreciation at December 31, 2019 | 1,350 |  |  |
Other | 920 North King Street |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 6,141 |  |  |
Buildings and Improvements | 21,140 |  |  |
Net Improvements (Retirements) Since Acquisition | 7,969 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 6,141 |  |  |
Buildings and Improvements | 29,109 |  |  |
Total | 35,250 |  |  |
Accumulated Depreciation at December 31, 2019 | 13,046 |  |  |
Other | 300 Delaware Avenue |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 |  |  |
Initial Cost [Abstract] |  |  |  |
Land | 6,369 |  |  |
Buildings and Improvements | 13,739 |  |  |
Net Improvements (Retirements) Since Acquisition | 2,638 |  |  |
Carrying Amount at Which Carried [Abstract] |  |  |  |
Land | 6,369 |  |  |
Buildings and Improvements | 16,377 |  |  |
Total | 22,746 |  |  |
Accumulated Depreciation at December 31, 2019 | $ 9,031 |  |  |

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