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Nature of Operations, Basis of Presentation, and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) | Sep. 30, 2020 | Feb. 07, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Stifel Credit Facility [Member] |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |
Credit facility | $ 300,000,000.0 |  |
North Shore Aviation Holdings LLC [Member] |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Parent |  |  | 27.50%
North Shore Aviation Holdings LLC [Member] | Stifel Credit Facility [Member] |  |  |
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items] |  |  |
Credit facility |  | $ 120,000,000.0 |

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