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Selected Balance Sheet Information: Accounts Receivable (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020 | Dec. 31, 2019
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Selected Balance Sheet Information [Abstract] |  |  |  |
Accounts receivable, trade | $ 199,548 | $ 146,899 |  |
Unbilled revenue | 91,085 | 126,065 |  |
Less: Allowance for doubtful accounts | (8,251) | (7,003) | $ (5,162) | $ (2,444)
Accounts receivable, net | $ 282,382 | $ 265,961 |  |

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