Stockholder's Equity (Deficit) (Tables)

9 Months Ended

Sep. 30, 2021

Summary of Issued Shares of Common Stock

The Company issued the following shares of common stock:

	Three Months Ended September 30,
	2021						2020
	Shares		Average Price per Share		Total Consideration (in thousands)		Shares			Average Price per Share		Total Consideration (in thousands)
Common stock issued in    connection initial public    offering		—	$	—	$	—		11,500,000		$	15.00	$	172,500
Acquisitions		62,738	$	52.18		3,274		—			—		—
Redemption of series A-1    preferred stock		—		—		—		1,786,739			15.00		26,801
Exercise of warrant options		—		—		—		2,534,239			0.01		25
Exercise of options		354,918		8.30		2,946		16,850			8.92		150
Restricted shares, net		—		—		—		8,333			24.00		—
Cancellation of shares		—		—		—		(117,785	)		17.15		—
Total		417,656	$	14.89	$	6,220		15,728,376		$	12.82	$	199,476
	Nine Months Ended September 30,
	2021						2020
	Shares		Average Price per Share		Total Consideration (in thousands)		Shares			Average Price per Share		Total Consideration (in thousands)
Common stock issued in    connection initial public    offering		—	$	—	$	—		11,500,000		$	15.00	$	172,500
Acquisitions		143,800		41.86		6,020		791,139			31.60		25,000
Redemption of series A-1    preferred stock		—		—		—		1,786,739			15.00		26,801
Exercise of warrant options		67,713		17.19		—		2,534,239			0.01		25
Exercise of options		779,068		7.74		6,032		20,350			9.27		189
Restricted shares, net		38,929		31.31		—		8,333			24.00		—
Payment of earn-out liability		539,607		46.33		25,000		—			—		—
Payment of purchase price    true up		24,200		44.81		1,084		—			—		—
Cancellation of shares		—		—		—		(117,785	)		17.15		—
Total		1,593,317	$	25.43	$	38,136		16,523,015		$	13.72	$	224,515

Schedule of Share Authorized to be Issue and Available for Grant

The following number of shares were authorized to be issued and available for grant:

	September 30, 2021
	2017 Plan		2013 Plan		Total
Shares authorized to be issued		3,944,750		2,047,269		5,992,019
Shares available for grant		1,593,287		—		1,593,287
	September 30, 2020
	2017 Plan		2013 Plan		Total
Shares authorized to be issued		2,945,443		2,047,269		4,992,712
Shares available for grant		1,233,266		—		1,233,266

Schedule of Stock Compensation Expense

Total stock compensation expense for the Plans was as follows:

	Three Months Ended September 30,
	2021								2020
	2017 plan				2013 plan				2017 plan				2013 plan
	Options		Restricted Stock		Options		Total		Options		Restricted Stock		Options			Total
Cost of revenue	$	282	$	—	$	—	$	282	$	276	$	—	$	(5	)	$	271
Selling, general and    administrative expense		1,844		237		2		2,083		592		233		53			878
Total	$	2,126	$	237	$	2	$	2,365	$	868	$	233	$	48		$	1,149
	Nine Months Ended September 30,
	2021								2020
	2017 plan				2013 plan				2017 plan				2013 plan
	Options		Restricted Stock		Options		Total		Options		Restricted Stock		Options			Total
Cost of revenue	$	1,178	$	—	$	10	$	1,188	$	973	$	—	$	126		$	1,099
Selling, general and    administrative expense		4,638		749		11		5,399		1,178		973		189			2,340
Total	$	5,816	$	749	$	21	$	6,587	$	2,151	$	973	$	315		$	3,439

Summary of Weighted Average Assumptions Used in Black-Sholes Option-pricing Model

The following weighted-average assumptions were used in the Black-Sholes option-pricing model calculation:

	September 30,		September 30,
	2021		2020
Common stock value (per share)	$	39.83	$	16.36
Expected volatility		58.34		46.14
Risk-free interest rate		0.77		0.41
Expected life (years)	5.5-7.0		7.0
Forfeiture rate	None		None
Dividend rate	None		None

Schedule of Common Stock Reserved for Future Issuance

Common Stock Reserved for Future Issuances—The Company has reserved certain stock of its authorized but unissued common stock for possible future issuance in connection with the following:

	September 30,
	2021		2020
Warrants		—		116,350
Montrose 2013 Stock Incentive Plan		2,047,269		2,047,269
Montrose 2017 Stock Incentive Plan		3,944,750		2,945,443
Common stock reserved for future issuance		5,992,019		5,109,062

Montrose Amended & Restated 2017 Stock Incentive Plan

Schedule of Restricted Stock Activity

Restricted stock activity was as follows:

	Nine Months Ended September 30,
	2021						2020
	Shares		Average Price per Share		Total (in thousands)		Shares		Average Price per Share		Total (in thousands)
Shares granted		19,066	$	36.99	$	705		33,229	$	31.60	$	1,050

Summary of Stock Option Activity

The following summarizes the options activity of the 2017 Plan:

	Options to Purchase Common Stock			Weighted- Average Exercise Price per Share		Weighted Average Grant Date Fair Value per Share		Weighted Average Remaining Contract Life (in Years)		Aggregate Intrinsic Value of In-The- Money Options (in Thousands)
Outstanding at January 1, 2020		617,852		$	24	$	12		7.82	$	4,693
Granted		851,877			32		12		—		—
Forfeited/ cancelled		(14,375	)		22		—		—		—
Exercised		(925	)		14		—		—		7,918
Outstanding at September 30, 2020		1,454,429			21		12		7.59		7,649
Outstanding at January 1, 2021		1,840,229			23		12		9.09		15,598
Granted		264,470			40		22		—		—
Forfeited/ cancelled		(29,025	)		28		—		—		—
Expired		(1,250	)		18		—		—		—
Exercised		(66,875	)		22		—		—		2,078
Outstanding at September 30, 2021		2,007,549			25		14		8.53		73,724
Exercisable at September 30, 2021		320,861			28		—		7.68		10,755
Options vested and expected to vest		2,007,549			25		—		8.53		73,724

Montrose Amended and Restated 2013 Stock Option Plan

Summary of Stock Option Activity

The following summarizes the activity of the 2013 Plan:

	Options to Purchase Common Stock			Weighted- Average Exercise Price per Share		Weighted Average Grant Date Fair Value per Share		Weighted Average Remaining Contract Life (in Years)		Aggregate Intrinsic Value of In-The- Money Options (in Thousands)
Outstanding at January 1, 2020		1,855,469		$	6	$	1		6.40		46,617
Forfeited/ cancelled		(7,500	)		10		—		—		—
Expired		(11,300	)		6		—		—		—
Exercised		(19,175	)		8		—		—		354
Outstanding at September 30, 2020		1,817,494			6		1		5.63		33,772
Outstanding at January 1, 2021		1,787,869			6		1		5.40		43,867
Expired		(625	)		6		—		—		—
Exercised		(710,568	)		6		—		—		33,480
Outstanding at September 30, 2021		1,076,676			6		2		4.65		59,532
Exercisable at September 30, 2021		1,076,676			6		—		4.65		59,532
Options vested and expected to vest		1,076,676			6		—		4.65		59,532