Stockholders' Equity - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options to Purchase Common Stock Exercised	(239,358)	(101,340)	(959,890)
Montrose 2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options to Purchase Common Stock Outstanding Beginning Balance	2,579,566	2,036,729	1,840,229
Options to Purchase Common Stock Granted	253,980	698,534	300,620
Options to Purchase Common Stock Forfeited/cancelled	(134,170)	(96,211)	(33,875)
Options to Purchase Common Stock Expired	(6,450)		(1,550)
Options to Purchase Common Stock Exercised	(176,654)	(59,486)	(68,695)
Options to Purchase Common Stock Outstanding Ending Balance	2,516,272	2,579,566	2,036,729	1,840,229
Options to Purchase Common Stock Exercisable	1,373,313
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price per Share Beginning Balance	$ 31	$ 26	$ 23
Weighted-Average Exercise Price per Share Granted	32	44	44
Weighted-Average Exercise Price per Share Forfeited/cancelled	36	32	28
Weighted-Average Exercise Price per Share Expired	32		19
Weighted-Average Exercise Price per Share Exercised	24	23	22
Weighted-Average Exercise Price per Share Ending Balance	31	31	26	$ 23
Weighted-Average Exercise Price per Share, Exercisable	30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value per Share Beginning Balance	15	14	12
Weighted Average Grant Date Fair Value per Share Granted	14	16	23
Weighted Average Grant Date Fair Value per Share Ending Balance	$ 16	$ 15	$ 14	$ 12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contract Life (in Years) Outstanding	7 years 10 days	7 years 9 months 3 days	8 years 3 months 18 days	9 years 1 month 2 days
Weighted Average Remaining Contract Life, Exercisable	6 years 5 months 8 days
Aggregate Intrinsic Value of In-The-Money Options Outstanding	$ 37,295	$ 91,030	$ 15,598
Aggregate Intrinsic Value of In-The-Money Options Exercised	3,726	1,398	2,169
Aggregate Intrinsic Value of In-The-Money Options Outstanding	13,825	$ 37,295	$ 91,030	$ 15,598
Aggregate Intrinsic Value of In-The-Money Options Exercisable	$ 8,198
Montrose Amended and Restated 2013 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options to Purchase Common Stock Outstanding Beginning Balance	855,695	897,674	1,787,869
Options to Purchase Common Stock Expired	(800)	(125)	(625)
Options to Purchase Common Stock Exercised	(62,704)	(41,854)	(889,570)
Options to Purchase Common Stock Outstanding Ending Balance	792,191	855,695	897,674	1,787,869
Options to Purchase Common Stock Exercisable	792,191
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price per Share Beginning Balance	$ 6	$ 6	$ 6
Weighted-Average Exercise Price per Share Expired	6	6	6
Weighted-Average Exercise Price per Share Exercised	7	6	6
Weighted-Average Exercise Price per Share Ending Balance	6	6	6	$ 6
Weighted-Average Exercise Price per Share, Exercisable	6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value per Share Beginning Balance	2	2	1
Weighted Average Grant Date Fair Value per Share Ending Balance	$ 2	$ 2	$ 2	$ 1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contract Life (in Years) Outstanding	2 years 4 months 17 days	3 years 3 months 21 days	4 years 4 months 13 days	5 years 4 months 24 days
Weighted Average Remaining Contract Life, Exercisable	2 years 4 months 17 days
Aggregate Intrinsic Value of In-The-Money Options Outstanding	$ 32,478	$ 57,529	$ 43,867
Aggregate Intrinsic Value of In-The-Money Options Exercised	1,950	1,626	45,161
Aggregate Intrinsic Value of In-The-Money Options Outstanding	20,380	$ 32,478	$ 57,529	$ 43,867
Aggregate Intrinsic Value of In-The-Money Options Exercisable	$ 20,380