Stockholder's Equity (Deficit) (Tables)

6 Months Ended

Jun. 30, 2021

Summary of Issued Shares of Common Stock

The Company issued the following shares of common stock:

	Three Months Ended June 30,
	2021						2020
	Shares		Average Price per Share		Total Consideration (in thousands)		Shares		Average Price per Share		Total Consideration (in thousands)
Acquisitions		9,322	$	50.95	$	475		791,139	$	31.60	$	25,000
Exercise of options		94,090		9.58		901		3,500		6.03		21
Restricted shares, net		2,112		56.31		—		—		—		—
Payment of earn-out liability		539,607		46.33		25,000		—		—		—
Payment of purchase price true up		24,200		44.81		1,084		—		—		—
Total		669,331	$	41.20	$	27,460		794,639	$	31.49	$	25,021
	Six Months Ended June 30,
	2021						2020
	Shares		Average Price per Share		Total Consideration (in thousands)		Shares		Average Price per Share		Total Consideration (in thousands)
Acquisitions		81,062	$	33.88	$	2,746		791,139	$	31.60	$	25,000
Exercise of warrants		67,713		17.19		—		—		—		—
Exercise of options		424,150		7.28		3,086		3,500		6.03		21
Restricted shares, net		38,929		31.31		—		—		—		—
Payment of earn-out liability		539,607		46.33		25,000		—		—		—
Payment of purchase price true up		24,200		44.81		1,084		—		—		—
Total		1,175,661	$	29.17	$	31,916		794,639	$	31.49	$	25,021

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:

	June 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		1,609,687		—		1,609,687
	June 30, 2020
	2017 Plan		2013 Plan		Total
Shares authorized to be issued		1,066,160		2,050,244		3,116,404
Shares available for grant		20,817		—		20,817

Schedule of Stock Compensation Expense

Total stock compensation expense for the Plans was as follows:

	Three Months Ended June 30,
	2021								2020
	2017 plan				2013 plan				2017 plan				2013 plan
	Options		Restricted Stock		Options		Total		Options		Restricted Stock		Options		Total
Cost of revenue	$	290	$	—	$	—	$	290	$	342	$	—	$	61	$	403
Selling, general and    administrative expense		1,790		330		6		2,126		299		370		68		737
Total	$	2,080	$	330	$	6	$	2,416	$	641	$	370	$	129	$	1,140
	Six Months Ended June 30,
	2021								2020
	2017 plan				2013 plan				2017 plan				2013 plan
	Options		Restricted Stock		Options		Total		Options		Restricted Stock		Options		Total
Cost of revenue	$	896	$	—	$	10	$	906	$	697	$	—	$	131	$	828
Selling, general and    administrative expense		2,794		512		9		3,315		586		740		136		1,462
Total	$	3,690	$	512	$	19	$	4,221	$	1,283	$	740	$	267	$	2,290

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:

	June 30,			June 30,
	2021			2020
Common stock value (per share)	$	38.23		$ 31.60
Expected volatility		58.22	%		45.26	%
Risk-free interest rate		0.73	%		0.49	%
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:

	June 30,
	2021		2020
Warrants		—		2,002,550
Montrose 2013 Stock Incentive Plan		2,047,269		2,050,244
Montrose 2017 Stock Incentive Plan		3,944,750		1,066,160
Common stock reserved for future issuance		5,992,019		5,118,954

Montrose Amended & Restated 2017 Stock Incentive Plan

Schedule of Restricted Stock Activity

Restricted stock activity was as follows:

	Three Months Ended June 30,
	2021						2020
	Shares		Average Price per Share		Total (in thousands)		Shares		Average Price per Share		Total (in thousands)
Shares granted		4,534	$	56.31	$	255		—	$	—	$	—
	Six Months Ended June 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	$	4,696
Granted		160,712			32		12		—		—
Forfeited/ cancelled		(5,500	)		20		—		—		—
Outstanding at June 30, 2020		773,064			26		12		8.03		4,651
Outstanding at January 1, 2021		1,840,229			23		12		9.09		15,598
Granted		232,470			38		21		—		—
Forfeited/ cancelled		(13,425	)		27		—		—		—
Expired		(1,250	)		18		—		—		—
Exercised		(33,918	)		20		—		—		1,014
Outstanding at June 30, 2021		2,024,106			25		13		8.74		58,785
Exercisable at June 30, 2021		293,299			25		—		7.65		8,396
Options vested and expected to vest		2,024,106			25		—		8.74		58,785

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		(1,250	)		6
Expired		(8,550	)		6		—		—		—
Exercised		(3,500	)		6
Outstanding at June 30, 2020		1,842,169			6		1		5.91		46,276
Outstanding at January 1, 2021		1,787,869			6		1		5.40		43,867
Exercised		(389,232	)		6		—		—		15,922
Outstanding at June 30, 2021		1,398,637			6		1		4.88		65,982
Exercisable at June 30, 2021		1,390,812			6		—		4.88		65,651
Options vested and expected to vest		1,398,637			6		—		4.88		65,982