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Significant Accounting Policies Update - Additional Information (Detail) | 9 Months Ended | 12 Months Ended
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Sep. 30, 2018 | Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items] |  |
U.S. corporate tax rate | 21.00% | 35.00%
Wholly Owned Property [Member] |  |
Summary Of Significant Accounting Policies [Line Items] |  |
Ownership interest in property | 100.00% |
Commercial Real Estate [Member] |  |
Summary Of Significant Accounting Policies [Line Items] |  |
Ownership interest in property | 0.00% |

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