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Real Estate - Allocation of Purchase Prices to Acquired Assets and Liabilities (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | --- | ---
Real Estate Properties [Line Items] |  |  |  |
Land | $ 511,482 |  |  |
Buildings | 1,543,837 |  |  |
Total Purchase Price | $ 2,124,796 | $ 2,081,597 | $ 1,948,165 | $ 1,803,200
Ashbrook Marketplace |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Land |  |  | 8,776 |
Buildings |  |  | 0 |
Total Purchase Price |  |  | 8,776 |
Ashbrook Marketplace | In-place Leases |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | 0 |
Ashbrook Marketplace | Above Market Rent |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | 0 |
Ashbrook Marketplace | Below Market Rent |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | 0 |
Hampden House (formerly 7316 Wisconsin Avenue) |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Land |  |  | 38,662 |
Buildings |  |  | 979 |
Total Purchase Price |  |  | 40,674 |
Hampden House (formerly 7316 Wisconsin Avenue) | In-place Leases |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | (886) |
Hampden House (formerly 7316 Wisconsin Avenue) | Above Market Rent |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | (168) |
Hampden House (formerly 7316 Wisconsin Avenue) | Below Market Rent |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | (21) |
2018 Acquisitions |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Land |  |  | 47,438 |
Buildings |  |  | 979 |
Total Purchase Price |  |  | 49,450 |
2018 Acquisitions | In-place Leases |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | (886) |
2018 Acquisitions | Above Market Rent |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | (168) |
2018 Acquisitions | Below Market Rent |  |  |  |
Real Estate Properties [Line Items] |  |  |  |
Intangible assets |  |  | $ (21) |

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- Definition Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 4 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6812-107765 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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- Definition Amount before accumulated deprecation and depletion of real estate held for productive use and additions or improvements to real estate held for productive use, examples include, but are not limited to, walkways, driveways, fences, and parking lots. Excludes land held for sale. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6812-107765 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(13)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(d)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition Amount of real estate owned for income production and capital accretion potential, not otherwise specified in the existing taxonomy. Such real estate excludes that which is occupied or used in the business, for entertainment purposes, or held in inventory for specific purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(d)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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