The following table summarizes the components of stock-based compensation expense recognized in the Company’s condensed consolidated statements of income for the periods indicated:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Cost of revenues (exclusive of depreciation and amortization)	$	12,174	$	10,854	$	34,552	$	23,796
Selling, general and administrative expenses	17,013		12,620		43,086		30,998
Total	$	29,187	$	23,474	$	77,638	$	54,794


	Number of Options	Weighted Average Exercise Price		Aggregate Intrinsic Value		Weighted Average Remaining Contractual Term (in years)
Options outstanding at January 1, 2021	2,772	$	61.71
Options granted	91	$	401.02
Options exercised	(418)	$	48.05
Options forfeited/cancelled	(12)	$	244.02
Options outstanding at September 30, 2021	2,433	$	75.85	$	1,203,190	3.8

Options vested and exercisable as of September 30, 2021	2,132	$	52.97	$	1,103,549	3.2
Options expected to vest as of September 30, 2021	280	$	236.20	$	93,728	8.4

As of September 30, 2021, $20.0 million of total remaining unrecognized stock-based compensation cost related to unvested stock options, net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 2.8 years.

The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the nine months ended September 30, 2021:


	Equity-Classified Restricted Stock			Equity-Classified Equity-Settled Restricted Stock Units			Liability-Classified Cash-Settled Restricted Stock Units
	Number of Shares	Weighted Average Grant Date Fair Value Per Share		Number of Shares	Weighted Average Grant Date Fair Value Per Share		Number of Shares	Weighted Average Grant Date Fair Value Per Share
Unvested service-based awards outstanding at January 1, 2021	9	$	167.18	686	$	162.15	175	$	141.16
Awards granted	—	$	—	221	$	411.89	27	$	392.93
Awards vested	—	$	—	(274)	$	132.67	(86)	$	117.80
Awards forfeited/cancelled	—	$	—	(33)	$	255.14	(3)	$	207.46
Unvested service-based awards outstanding at September 30, 2021	9	$	167.18	600	$	262.54	113	$	216.32

As of September 30, 2021, $0.5 million of total remaining unrecognized stock-based compensation cost related to service-based equity-classified restricted stock is expected to be recognized over the weighted-average remaining requisite service period of 0.9 years.

As of September 30, 2021, $116.1 million of total remaining unrecognized stock-based compensation cost related to service-based equity-classified restricted stock units (“RSUs”), net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 2.8 years.

During the nine months ended September 30, 2021, the Company granted 29 thousand service-based equity-classified RSUs in connection with the PolSource acquisition, 3 thousand service-based equity-classified RSUs in connection with the CORE acquisition and 14 thousand service-based equity-classified RSUs in connection with the Other 2021 Acquisitions. See Note 2 “Acquisitions” in the condensed consolidated interim financial statements for additional information regarding business acquisitions.

As of September 30, 2021, $39.1 million of total remaining unrecognized stock-based compensation cost related to service-based liability-classified cash-settled RSUs, net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 2.4 years.

The liability associated with the service-based liability-classified RSUs as of September 30, 2021 and December 31, 2020, was $20.4 million and $26.8 million, respectively, and was classified as Accrued compensation and benefits expenses in the condensed consolidated balance sheets.

The table below summarizes activity related to the Company’s equity-classified performance-based awards for the nine months ended September 30, 2021:


	Equity-Classified Equity-Settled Restricted Stock			Equity-Classified Equity-Settled Restricted Stock Units
	Number of Shares	Weighted Average Grant Date Fair Value Per Share		Number of Shares	Weighted Average Grant Date Fair Value Per Share
Unvested performance-based awards outstanding at January 1, 2021	9	$	165.87	21	$	227.16
Awards granted	—	$	—	1	$	399.99
Unvested performance-based awards outstanding at September 30, 2021	9	$	165.87	22	$	233.43

As of September 30, 2021, $0.7 million of total remaining unrecognized stock-based compensation cost related to performance-based equity-classified restricted stock is expected to be recognized over the weighted-average remaining requisite service period of 1.9 years.

As of September 30, 2021, $1.8 million of total remaining unrecognized stock-based compensation cost related to performance-based equity-classified RSUs is expected to be recognized over the weighted-average remaining requisite service period of 2.0 years.

During the nine months ended September 30, 2021, in connection with the PolSource acquisition, the Company granted 1 thousand performance-based equity-settled RSUs. Vesting of these performance-based equity-settled RSUs is dependent on continued service and achievement of certain revenue, earnings and operational targets.

Also, in connection with the CORE acquisition, the Company has committed to issuing $34.9 million of equity-settled awards with performance conditions to be granted at future stock prices over the next 3.4 years. These awards have a two year vesting period post issuance.

Additionally, during the nine months ended September 30, 2021, the Company issued certain performance-based equity-settled RSUs with undetermined conditions for future vesting, which are not deemed granted and outstanding for accounting purposes, and therefore they have been excluded from the awards granted disclosure and recognized expense for the period presented. The Company issued 5 thousand of such performance-based equity-settled RSUs in connection with the PolSource acquisition and 2 thousand of such performance-based equity-settled RSUs in connection with the Other 2021 Acquisitions. See Note 2 “Acquisitions” in the condensed consolidated interim financial statements for additional information regarding business acquisitions.

As of September 30, 2021, the Company has committed to issuing 6 thousand RSUs to employees of PolSource and future RSU awards valued at $3.8 million to employees of Other 2021 Acquisitions at various dates over the next 12 months. As of September 30, 2021, these awards were not considered granted for accounting purposes.