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Revenue - Narratives (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disaggregation of Revenue |  |  |  |  |  |  |  |  |  |  |
Total net sales | $ 115,576 | $ 118,365 | $ 141,563 | $ 121,907 | $ 141,331 | $ 144,848 | $ 190,701 | $ 139,548 | $ 497,411 | $ 616,428 | $ 581,064
Contract with customer, assets | 37,843 |  |  |  | 37,032 |  |  |  | 37,843 | 37,032 |
Contract assets transferred to receivables |  |  |  |  |  |  |  |  | 27,126 | 24,487 |
Cash proceeds from liability contract |  |  |  |  |  |  |  |  | 803 | 4,358 |
Revenue recognized from contract liability |  |  |  |  |  |  |  |  | 3,784 | 1,462 | $ 1,141
Deferred revenue (Note 4) | 7,144 |  |  |  | 8,446 |  |  |  | 7,144 | 8,446 |
Contract liabilities | $ 1,324 |  |  |  | $ 4,472 |  |  |  | $ 1,324 | $ 4,472 |
Over time |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue |  |  |  |  |  |  |  |  |  |  |
Customer revenue transferred (percentage) |  |  |  |  |  |  |  |  | 29.40% | 30.30% | 28.10%
Total net sales |  |  |  |  |  |  |  |  | $ 146,020 | $ 186,775 | $ 163,253
Over time | Performance Based |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue |  |  |  |  |  |  |  |  |  |  |
Total net sales |  |  |  |  |  |  |  |  | 101,160 | 136,014 | 121,919
Over time | Delivery Based |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue |  |  |  |  |  |  |  |  |  |  |
Total net sales |  |  |  |  |  |  |  |  | $ 44,860 | $ 50,761 | $ 41,334
Point in time |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue |  |  |  |  |  |  |  |  |  |  |
Customer revenue transferred (percentage) |  |  |  |  |  |  |  |  | 70.60% | 69.70% | 71.90%
Total net sales |  |  |  |  |  |  |  |  | $ 351,391 | $ 429,653 | $ 417,811

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