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Basis of Presentation and Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2019 | Dec. 31, 2018 | Mar. 31, 2018
Revenue from External Customer [Line Items] |  |  |
Revenue | $ 17,991 |  | $ 14,718
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 | $ 2,700 |  |
Minimum |  |  |
Revenue from External Customer [Line Items] |  |  |
Amortization period of capitalized contract costs | 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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