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Stockholder's Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020 | May 31, 2015
Class Of Stock [Line Items] |  |  |  |
Common stock, shares authorized | 190,000,000 |  | 190,000,000 |
Common stock, par value | $ 0.000004 |  | $ 0.000004 |
Stock issued on exercise of warrants | 67,713 |  |  |
Total unrecognized stock compensation expense related to unvested options and restricted stock granted under the Plans | $ 18.8 | $ 7.2 |  |
Unrecognized expense expected to be recognized period | 3 years |  |  |
Montrose Amended & Restated 2017 Stock Incentive Plan |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Number of restricted stock shares issued | 14,532 | 33,229 |  |
Restricted stock fair value market price per share | $ 30.96 | $ 31.60 |  |
Restricted shares became fully vested and released as common stock | 36,817 | 0 |  |
Restricted shares outstanding | 281,705 | 273,122 |  |
Restricted shares forfeited | 0 | 0 |  |
Montrose Amended & Restated 2017 Stock Incentive Plan | Restricted Stock |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Shares of vested over period | 1 year |  |  |
Montrose Amended & Restated 2017 Stock Incentive Plan | Stock Options | Board of Directors |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Shares of vested over period | 4 years |  |  |
Montrose Amended & Restated 2017 Stock Incentive Plan | Stock Options | Executive Officers |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Shares of vested over period | 3 years |  |  |
Vesting frequency of period | 1 year |  |  |
Montrose Amended & Restated 2017 Stock Incentive Plan | Stock Options | Second Anniversary | Board of Directors |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Award vesting percentage | 50.00% |  |  |
Montrose Amended & Restated 2017 Stock Incentive Plan | Stock Options | Fourth Anniversary | Board of Directors |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Award vesting percentage | 50.00% |  |  |
Montrose Amended and Restated 2013 Stock Option Plan |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Shares outstanding from exercised options | 579,260 | 201,600 |  |
Private Offering |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Warrants to purchase common stock |  |  |  | 116,350
Warrant exercise price per share |  |  |  | $ 17.19

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