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Commitments and Contingencies - Narrative (Details) | May 25, 2017 USD ($) | Dec. 31, 2017 USD ($) Property | Dec. 31, 2016 USD ($) | Aug. 31, 2010 USD ($)
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Capital Lease |  |  |  |
Capital lease term | 99 years |  |  |
Purchase option | $ 1 |  |  |
Capital lease obligation | $ 16,100,000 | $ 15,853,000 | $ 0 |
Environmental Indemnity Agreement |  |  |  |
Number of lease properties which were provided environmental indemnifications | Property |  | 3 |  |
Maximum environmental indemnification to the tenant against consequential damages after acquisition of property |  | $ 19,000,000 |  |
Specialty Tax Guarantee [Member] |  |  |  |
Tax incremental financing obligation |  |  |  |
Liability recognized with regard to tax incremental financing obligation at end of current period |  | 981,000 |  |
New Development and Redevelopment Obligations [Member] |  |  |  |
Capital Lease |  |  |  |
Contractual obligation |  | 22,800,000 |  |
Capital Expenditures For Operating Properties [Member] |  |  |  |
Capital Lease |  |  |  |
Contractual obligation |  | 44,200,000 |  |
Third Party Construction and Development [Member] |  |  |  |
Capital Lease |  |  |  |
Contractual obligation |  | 35,800,000 |  |
Other Obligations [Member] |  |  |  |
Capital Lease |  |  |  |
Contractual obligation |  | $ 900,000 |  |
Tax Incremental Financing Bond [Member] | Anne Arundel County, Maryland [Member] | Specialty Tax Guarantee [Member] |  |  |  |
Commitments and Contingencies |  |  |  |
Loan amount |  |  |  | $ 30,000,000

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