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Stock-Based Compensation - Additional Information (Detail) |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Apr. 17, 2018 Installment shares | Nov. 29, 2017 shares | Oct. 11, 2017 shares | Dec. 31, 2019 USD ($) $ / shares shares | May 31, 2018 $ / shares shares | Mar. 31, 2020 USD ($) shares | Mar. 31, 2019 USD ($) shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2017 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares available for issuance |  |  |  | 4,162,361 |  | 5,983,578 |  | 4,162,361 | 2,773,249 |
Recognized stock-based compensation expense | $ |  |  |  |  |  | $ 975,000 | $ 663,000 | $ 3,694,000 | $ 2,793,000 | $ 470,000
Options Issued and Outstanding |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares available for issuance |  |  |  | 2,562,800 |  | 2,302,435 |  | 2,562,800 | 1,122,677 |
Aggregate intrinsic value of options exercised | $ |  |  |  |  |  |  |  | $ 67,000 | $ 78,000 |
Options granted |  |  |  |  |  |  |  | 1,896,527 |  |
Number of options exercised |  |  |  |  |  | 0 |  | 7,029 |  |
Options Issued and Outstanding | Employees and Directors |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Option granted |  |  |  |  |  | 0 |  | 1,886,687 |  |
Weighted-average grant date fair value of options granted | $ / shares |  |  |  |  |  |  |  | $ 4.83 |  |
Expense related to options granted | $ |  |  |  |  |  | $ 900,000 | 600,000 |  |  |
Options Issued and Outstanding | Employees |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Option granted |  |  |  |  |  |  |  |  | 926,838 |
Weighted-average grant date fair value of options granted | $ / shares |  |  |  |  |  |  |  |  | $ 9.23 |
Unrecognized compensation expense | $ |  |  |  | $ 9,400,000 |  | $ 7,300,000 |  | $ 9,400,000 |  |
Unrecognized compensation expense, estimated weighted-average period for recognition |  |  |  |  |  | 2 years 7 months 6 days |  | 2 years 9 months 18 days |  |
Options Issued and Outstanding | Non-employees |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Options granted |  |  |  |  |  |  |  | 9,840 | 7,200 |
Weighted-average grant date fair value of options granted | $ / shares |  |  |  |  |  |  |  | $ 7.61 | $ 12.51 |
Unrecognized compensation expense | $ |  |  |  | 26,000.0 |  | $ 15,000.0 |  | $ 26,000.0 |  |
Unrecognized compensation expense, estimated weighted-average period for recognition |  |  |  |  |  | 1 year 10 months 24 days |  | 2 years 1 month 20 days |  |
Expense related to options granted | $ |  |  |  |  |  | $ 1,000 | 7,000 |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares granted | 2,000 |  |  |  |  |  |  |  |  |
Number of quarterly installment in which restriction lapse | Installment | 4 |  |  |  |  |  |  |  |  |
Recognized stock-based compensation expense | $ |  |  |  |  |  |  |  | $ 4,000.0 | $ 900,000 | $ 400,000
Unrecognized stock-based compensation expense | $ |  |  |  | $ 0 |  |  |  | $ 0 |  |
Restricted stock units |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares available for issuance |  |  |  | 828,935 |  | 753,863 |  | 828,935 | 24,960 |
Unrecognized compensation expense, estimated weighted-average period for recognition |  |  |  |  |  | 3 years 6 months |  | 3 years 9 months |  |
Shares granted |  |  |  |  |  |  |  | 813,335 |  |
Recognized stock-based compensation expense | $ |  |  |  |  |  | $ 71,000 | $ 14,000 | $ 74,000 | $ 35,000 |
Unrecognized stock-based compensation expense | $ |  |  |  | $ 1,100,000 |  | $ 1,000,000 |  | $ 1,100,000 |  |
Restricted stock units | Employees |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares granted |  |  |  | 813,335 | 24,960 |  |  |  |  |
Weighted-average grant date fair value | $ / shares |  |  |  | $ 1.27 | $ 9.03 |  |  |  |  |
2017 Stock Incentive Plan |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares reserved for issuance |  | 630,662 | 537,914 | 537,914 |  | 537,914 |  | 537,914 |  |
Number of additional shares reserved for issuance |  | 1,866,009 | 630,662 |  |  |  |  |  |  |
2017 Stock Incentive Plan | Maximum |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Terms of stock based options granted |  |  |  |  |  | 10 years |  | 10 years |  |
2018 Stock Incentive Plan |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Percentage of additional shares added on outstanding shares |  |  |  |  |  |  | 4.00% | 4.00% |  |
Shares available for issuance |  |  |  | 0 |  | 0 |  | 0 |  |
2018 Stock Incentive Plan | Minimum |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares reserved for issuance |  |  |  | 2,200,260 |  | 3,322,473 | 2,200,260 | 2,200,260 |  |
2018 Stock Incentive Plan | Maximum |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares reserved for issuance |  |  |  | 3,322,473 |  | 4,780,262 | 3,322,473 | 3,322,473 |  |
2018 Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares reserved for issuance |  |  |  |  |  |  |  |  | 275,030 |
Percentage of additional shares added on outstanding shares |  |  |  |  |  |  |  |  | 1.00% |
Number of shares available for sale |  |  |  |  |  | 0 | 0 | 0 | 0 |
2018 Employee Stock Purchase Plan | Minimum |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of additional shares reserved for issuance |  |  |  |  |  | 543,926 |  |  | 543,926 |
2018 Employee Stock Purchase Plan | Maximum |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of additional shares reserved for issuance |  |  |  |  |  | 920,030 |  | 555,583 | 555,583 |

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