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Real Estate and Accumulated Depreciation Activity of Real Estate and Accumulated Depreciation (BPLP) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward] |  |  |
Real Estate, Balance at the beginning of the year | $ 20,114,576 | $ 19,451,683 | $ 19,208,417
Real Estate, Additions to / improvements of real estate | 1,099,286 | 977,287 | 700,792
Real Estate, Assets sold / written off | (155,148) | (314,394) | (457,526)
Real Estate, Balance at the end of the year | 21,058,714 | 20,114,576 | 19,451,683
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] |  |  |
Accumulated depreciation, Balance at beginning of the year | 4,201,891 | 3,905,940 | 3,529,978
Accumulated depreciation, Depreciation expense | 497,059 | 560,024 | 486,450
Accumulated depreciation, Assets sold / written off | (132,380) | (264,073) | (110,488)
Accumulated depreciation, Balance at end of the year | 4,566,570 | 4,201,891 | 3,905,940
Boston Properties Limited Partnership |  |  |
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward] |  |  |
Real Estate, Balance at the beginning of the year | 19,701,185 | 19,031,289 | 18,786,572
Real Estate, Additions to / improvements of real estate | 1,099,286 | 977,287 | 700,792
Real Estate, Assets sold / written off | (153,235) | (307,391) | (456,075)
Real Estate, Balance at the end of the year | 20,647,236 | 19,701,185 | 19,031,289
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] |  |  |
Accumulated depreciation, Balance at beginning of the year | 4,116,020 | 3,826,862 | 3,458,640
Accumulated depreciation, Depreciation expense | 488,919 | 548,397 | 478,457
Accumulated depreciation, Assets sold / written off | (131,044) | (259,239) | (110,235)
Accumulated depreciation, Balance at end of the year | $ 4,473,895 | $ 4,116,020 | $ 3,826,862

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