Stockholder's Equity - Additional Information (Details) - USD ($)		3 Months Ended		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2021	Dec. 31, 2023
Class Of Stock [Line Items]
Common stock, shares authorized		190,000,000			190,000,000
Common stock, par value		$ 0.000004			$ 0.000004
Total unrecognized stock-based compensation expense related to unvested options, restricted stock and stock appreciation rights granted under the Plans		$ 113,800,000	$ 146,600,000
Unrecognized expense expected to be recognized period		3 years
Stock compensation expenses		$ 11,272,000	$ 13,035,000
Shares, granted	[1]	144,251	90,116
Restricted shares outstanding		3,090,801	2,528,383
Montrose 2017 Stock Incentive Plan | Restricted Stock
Class Of Stock [Line Items]
Shares, granted		0	0
Montrose 2017 Stock Incentive Plan | Stock Options | Board of Directors
Class Of Stock [Line Items]
Shares of vested over period		4 years
Montrose 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 2017 Stock Incentive Plan | Stock Options | On the two-year anniversary of the grant | Board of Directors
Class Of Stock [Line Items]
Shares, vesting rights, percentage		50.00%
Montrose 2017 Stock Incentive Plan | Stock Options | Fourth Anniversary | Board of Directors
Class Of Stock [Line Items]
Shares, vesting rights, percentage		50.00%
Montrose Amended and Restated 2013 Stock Option Plan
Class Of Stock [Line Items]
Shares outstanding from exercised options		1,577,184	1,434,885
Two Thousand Seventeen Plan | Restricted Stock
Class Of Stock [Line Items]
Stock compensation expenses		$ 7,919,000	$ 8,697,000
Two Thousand Seventeen Plan | Stock Options
Class Of Stock [Line Items]
Stock compensation expenses		1,063,000	2,073,000
Two Thousand Seventeen Plan | Stock Appreciation Rights (SARs)
Class Of Stock [Line Items]
Stock compensation expenses		$ 2,290,000	2,265,000
Shares, granted		3,000,000
Exercise price				$ 66.79
Shares of vested over period				5 years
Remaining contractual terms		10 years
Fair value vested in period		$ 46,000,000
Weighted average remaining contract life		7 years 8 months 15 days
2013 Plan
Class Of Stock [Line Items]
Stock compensation expenses		$ 0	$ 0
Supplemental Incentive Plans
Class Of Stock [Line Items]
Shares, granted		0	246,417
Supplemental Incentive Plans | RSUs
Class Of Stock [Line Items]
Shares of vested over period		4 years
Supplemental Incentive Plans | RSUs | First Quater
Class Of Stock [Line Items]
Shares, vesting rights, percentage		33.33%
Supplemental Incentive Plans | RSUs | First Anniversary
Class Of Stock [Line Items]
Shares, vesting rights, percentage		33.33%
Supplemental Incentive Plans | RSUs | Second Anniversary
Class Of Stock [Line Items]
Shares, vesting rights, percentage		33.33%

[1] Represents the non-cash release of common shares due to the vesting of restricted stock.