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Basis of Presentation and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Revenue from External Customer [Line Items] |  |  |  |  |
Revenue | $ 19,895 |  | $ 18,204 | $ 37,886 | $ 32,922
Additions to tax positions of prior years |  | $ 547 |  |  |
Income tax penalties and interest accrued |  | 55 |  |  |
Bill and Hold Arrangement |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |
Revenue |  |  |  | $ 6,100 |
Minimum |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |
Amortization period of capitalized contract costs | 1 year |  |  | 1 year |
Tax Year 2017 |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |
Additions to tax positions of prior years |  | 168 |  |  |
Tax Year 2016 |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |
Additions to tax positions of prior years |  | 149 |  |  |
Tax Year 2015 |  |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |  |
Additions to tax positions of prior years |  | $ 230 |  |  |

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