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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 15, 2017 | Dec. 31, 2017 | Feb. 28, 2018 | Dec. 31, 2016
Property, Plant and Equipment [Line Items] |  |  |  |
Percentage holding required to account investments under non-marketable equity investments |  | 20.00% |  |
Percentage of dividend | 10.00% |  |  |
Retained earnings |  | $ 59,314 |  | $ 118,363
Subsequent Event [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Retained earnings |  |  | $ 2,286 |
Building [Member] | Maximum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives |  | 40 years |  |
Leasehold Improvements [Member] | Minimum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives |  | 10 years |  |
Software, Equipment, Furniture and Fixtures [Member] | Maximum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives |  | 7 years |  |
Software, Equipment, Furniture and Fixtures [Member] | Minimum [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Estimated useful lives |  | 3 years |  |

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