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Income Taxes (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Operating Loss Carryforwards [Line Items] |  |  |
U.S federal corporate tax rate | 21.00% | 21.00% |
Valuation allowance increase (decrease) | $ (1,300) |  |
Unrecognized tax benefits | 4,500 | $ 4,400 | $ 4,400
Write Down Of Share-Based Compensation [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Valuation allowance increase (decrease) | (2,400) |  |
Book Losses [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Valuation allowance increase (decrease) | 1,100 | $ 900 |
Federal [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Pre-tax net operating loss carryforwards | 87,300 |  |
Federal [Member] | Expires Between 2029 And 2039 [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Pre-tax net operating loss carryforwards | 74,100 |  |
Federal [Member] | Indefinitely [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Pre-tax net operating loss carryforwards | 13,200 |  |
Federal [Member] | Expires Between 2023 And 2039 [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Federal research and development tax credits | $ 11,100 |  |
Federal [Member] | Minimum [Member] | Expires Between 2029 And 2039 [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Expiration date of pre-tax net operating loss carryforwards | Jan. 01, 2029 |  |
Federal [Member] | Minimum [Member] | Expires Between 2023 And 2039 [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Expiration date of federal research and development tax credits | Jan. 01, 2023 |  |
Federal [Member] | Maximum [Member] | Expires Between 2029 And 2039 [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Expiration date of pre-tax net operating loss carryforwards | Dec. 31, 2039 |  |
Federal [Member] | Maximum [Member] | Expires Between 2023 And 2039 [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Expiration date of federal research and development tax credits | Dec. 31, 2040 |  |

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