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Stock-based Compensation Expense - Summary of Restricted Stock Activity under 2019 Plan and 2016 Plan (Details) - 2019 Plan and 2016 Plan - Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Number of Shares, Unvested, Beginning balance 346,423 757,022
Number of Shares, Vested (233,563) (349,149)
Number of Shares, Repurchased (29,882) (61,450)
Number of Shares, Unvested, Ending balance 82,978 346,423
Weighted Average Grant Date Fair Value, Unvested, Beginning balance $ 3.05 $ 3.07
Weighted Average Grant Date Fair Value, Vested 3.00 3.10
Weighted Average Grant Date Fair Value, Repurchased 3.05 3.02
Weighted Average Grant Date Fair Value, Unvested, Ending balance $ 3.19 $ 3.05