Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 16, 2021	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
Treasury stock purchase price			$ 9.80
Commitments to repurchase capital stock			0
Total unrecognized stock compensation expense related to unvested options, restricted stock and stock appreciation rights granted under the Plans	$ 170,100
Unrecognized expense expected to be recognized period	5 years
Shares of vested over period	1 year	1 year
Shares, granted	42,263	20,488	12,132
Share based compensation expense	$ 10,321	$ 4,849	$ 4,345
Shares reserved for future issuance	8,968,866	5,109,062	3,706,994
Restricted shares became fully vested and released as common stock	42,263,000	22,155,000	12,132,000
Restricted shares outstanding	1,957,873,000	267,173,000	239,893,000
Restricted shares forfeited	0	1,667,000	0
Supplemental Incentive Plans
Class Of Stock [Line Items]
Shares, granted	0
Montrose Amended & Restated 2017 Stock Incentive Plan
Class Of Stock [Line Items]
Shares of vested over period	5 years
Shares, granted	1,671,391
Share based, description	These RSUs represent the right to receive one share of the Company’s common stock upon vesting. These incentives were designed by the Board, in coordination with the Company’s compensation advisors, to (i) retain selected employees of the Company for a minimum of 5 years, (ii) reward selected employees for the Company’s significant outperformance and stockholder value creation in 2021, and (iii) provide incentives to selected employees of the Company to accelerate value creation for stockholders and other stakeholders over the next five-year period.
Share based compensation expense	$ 90,000
Shares reserved for future issuance	6,921,597	2,945,443	997,785	135,517
Montrose Amended and Restated 2013 Stock Option Plan
Class Of Stock [Line Items]
Shares outstanding from exercised options	1,209,090,000	249,200,000	201,600,000
RSUs | Montrose Amended & Restated 2017 Stock Incentive Plan
Class Of Stock [Line Items]
Shares, granted	1,355,182
Shares, vesting rights, percentage	50.00%
Performance-Vested RSUs | Montrose Amended & Restated 2017 Stock Incentive Plan
Class Of Stock [Line Items]
Shares, granted	316,209
Shares, vesting rights, percentage	50.00%
Stock Appreciation Rights (SARs) | Two Thousand Seventeen Plan
Class Of Stock [Line Items]
Shares of vested over period	5 years
Shares, granted	3,000,000
Share based compensation expense	$ 307
Exercise price	$ 66.79
Remaining contractual terms	10 years
Fair value vested in period	$ 46,000
Stock Options | Montrose Amended & Restated 2017 Stock Incentive Plan | Board of Directors
Class Of Stock [Line Items]
Shares of vested over period	4 years
Stock Options | Montrose Amended & Restated 2017 Stock Incentive Plan | Executive Officers
Class Of Stock [Line Items]
Shares of vested over period	3 years
Stock Options | Two Thousand Seventeen Plan
Class Of Stock [Line Items]
Share based compensation expense	$ 8,034	$ 3,234	$ 1,615
Private Offering
Class Of Stock [Line Items]
Warrants to purchase common stock					116,350
Warrant exercise price per share					$ 17.19