Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($)
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12 Months Ended |
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Jan. 01, 2018 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Jan. 01, 2019 |
Dec. 31, 2017 |
| Recently Adopted Accounting Pronouncements |
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| Additional paid-in capital |
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$ 621,946,000
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$ 586,798,000
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$ 17,277,000
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| Accumulated deficit |
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(480,471,000)
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(312,740,000)
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$ (150,082,000)
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(60,979,000)
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| Change in fair value of the unvested awards |
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$ 141,560,000
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274,213,000
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393,008,000
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(43,687,000)
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| Lease, Practical Expedients, Package [true false] |
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true
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| Financial impact on the Company's condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment |
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| Operating lease, right-of-use-asset |
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$ 40,447,000
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46,559,000
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| Property, plant and equipment, net |
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53,952,000
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56,924,000
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62,796,000
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| Deferred rent |
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143,000
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| Accrued expenses and other current liabilities |
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12,118,000
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| Accrued expenses and other current liabilities |
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13,417,000
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16,042,000
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| Lease financing obligation |
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41,441,000
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| Operating lease liabilities, current portion |
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8,945,000
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10,540,000
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| Operating lease liabilities, net of current portion |
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32,762,000
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36,867,000
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| Accumulated deficit |
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(480,471,000)
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(312,740,000)
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(150,082,000)
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(60,979,000)
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| Accumulated deficit |
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| Recently Adopted Accounting Pronouncements |
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| Change in fair value of the unvested awards |
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$ (480,471,000)
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(312,740,000)
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(150,082,000)
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$ (60,979,000)
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| Adjustments |
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| Recently Adopted Accounting Pronouncements |
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| Change in fair value of the unvested awards |
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800,000
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| Adjustments | Accumulated deficit |
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| Recently Adopted Accounting Pronouncements |
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| Change in fair value of the unvested awards |
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$ 800,000
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$ 92,000
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| Adjustments | ASU 2016-02 |
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| Recently Adopted Accounting Pronouncements |
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| Accumulated deficit |
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$ 800,000
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| Financial impact on the Company's condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment |
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| Operating lease, right-of-use-asset |
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1,751,000
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| Property, plant and equipment, net |
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(45,142,000)
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| Deferred rent |
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(143,000)
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| Accrued expenses and other current liabilities |
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(4,451,000)
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| Lease financing obligation |
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(41,441,000)
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| Operating lease liabilities, current portion |
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616,000
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| Operating lease liabilities, net of current portion |
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1,226,000
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| Accumulated deficit |
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800,000
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| Adjustments | ASU 2018-07 |
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| Recently Adopted Accounting Pronouncements |
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| Additional paid-in capital |
$ (92,000)
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| Accumulated deficit |
92,000
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| Change in fair value of the unvested awards |
100,000
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| Financial impact on the Company's condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment |
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| Accumulated deficit |
92,000
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| Balance as adjusted | ASU 2016-02 |
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| Recently Adopted Accounting Pronouncements |
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| Accumulated deficit |
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(149,282,000)
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| Financial impact on the Company's condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment |
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| Operating lease, right-of-use-asset |
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1,751,000
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| Property, plant and equipment, net |
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17,654,000
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| Accrued expenses and other current liabilities |
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7,667,000
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| Operating lease liabilities, current portion |
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616,000
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| Operating lease liabilities, net of current portion |
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1,226,000
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| Accumulated deficit |
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$ (149,282,000)
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| Balance as adjusted | ASU 2018-07 |
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| Recently Adopted Accounting Pronouncements |
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| Additional paid-in capital |
17,185,000
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| Accumulated deficit |
(60,887,000)
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| Financial impact on the Company's condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment |
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| Accumulated deficit |
$ (60,887,000)
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| Non-employees |
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| Assumptions used to determine the fair value of outstanding awards granted |
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| Risk-free interest rate |
2.30%
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1.10%
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2.07%
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2.71%
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| Expected volatility |
74.00%
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69.40%
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76.90%
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74.00%
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| Expected term (in years) |
6 years 1 month 6 days
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6 years 18 days
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6 years 21 days
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6 years 2 months 15 days
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| Common stock value |
$ 6.28
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| Non-employees | Unvested restricted common stock |
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| Assumptions used to determine the fair value of outstanding awards granted |
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| Number of outstanding options |
4,767,014
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| Weighted average grant-date fair value (per share) |
$ 5.88
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| Non-employees | Stock options to purchase common stock |
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| Assumptions used to determine the fair value of outstanding awards granted |
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| Number of outstanding options |
330,917
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