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Significant Accounting Policies - Acquired Unfavorable Real Estate Leases and Amortization (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) item | Dec. 31, 2015 USD ($) item
Acquired Unfavorable Real Estate Leases and Amortization |  |  |
Number of acquisitions of properties with leases | item |  | 3 | 1
Acquired unfavorable real estate leases |  |  |
Acquired Unfavorable Real Estate Leases and Amortization |  |  |
Amortization | $ 3,117,000 | $ 3,292,000 | $ 3,242,000
Estimated annual amortization for succeeding five years |  |  |
2018 | 2,039,000 |  |
2019 | 1,319,000 |  |
2020 | 950,000 |  |
2021 | 620,000 |  |
2022 | 346,000 |  |
2023 and thereafter | $ 532,000 |  |
Acquired unfavorable real estate leases | Minimum |  |  |
Acquired Unfavorable Real Estate Leases and Amortization |  |  |
Term of lease | 7 months |  |
Acquired unfavorable real estate leases | Maximum |  |  |
Acquired Unfavorable Real Estate Leases and Amortization |  |  |
Term of lease | 176 months |  |

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- Definition Amount of amortization income for leases with a finite life acquired as part of a real property acquisition at below market lease rate expected to be recognized after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References No definition available. + Details
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- Definition Amount of amortization income for leases with a finite life acquired as part of a real property acquisition at below market lease rate expected to be recognized during the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References No definition available. + Details
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- Definition Amount of amortization income for leases with a finite life acquired as part of a real property acquisition at below market lease rate expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References No definition available. + Details
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- Definition Amount of amortization income for leases with a finite life acquired as part of a real property acquisition at below market lease rate expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References No definition available. + Details
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