Real Estate and Intangible Assets - Components of Investments in Real Estate (Detail) - USD ($) $ in Thousands  | 
Sep. 30, 2020  | 
Dec. 31, 2019  | 
|---|---|---|
| Real estate: | ||
| Land | $ 140,465 | $ 137,532 | 
| Building and improvements | 886,138 | 851,245 | 
| Tenant improvements | 68,251 | 68,201 | 
| Accumulated depreciation | (221,849) | (207,523) | 
| Total real estate, net | 873,005 | $ 849,455 | 
| Land value subject to land lease agreements | $ 4,436 | 
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- Definition Land Subject to Land Lease Agreements, Value No definition available. 
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- Definition Aggregate of the carrying amounts as of the balance sheet date of investments in building and building improvements. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Amount before accumulated depletion of real estate held for productive use, excluding land held for sale. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition The cumulative amount of depreciation for real estate property held for investment purposes. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- References No definition available. 
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- Definition Amount of real estate investment property, net of accumulated depreciation, 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. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Carrying amount as of the balance sheet date of improvements having a life longer than one year that were made for the benefit of one or more tenants. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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