Total share-based compensation included in net income for the years ended December 31, 2021, January 1, 2021, and December 27, 2019, is as follows:

	Year Ended
	December 31,		January 1,		December 27,
	2021		2021		2019
Restricted stock units	$	9,716	$	8,676	$	6,762
Common stock subject to vesting requirements		406		1,064		954
	$	10,122	$	9,740	$	7,716

The number of shares available for future issuance under the Company's stock plans as of December 31, 2021, were 1,162,406. The Company issues new shares as they are required to be delivered under the plan.

The Company has granted stock options to employees and directors of the Company at exercise prices equal to the fair value of the stock at the date of grant. The options generally vest ratably over four years, based on continued employment, with a maximum term of ten years. Stock option activity under the Company’s stock option plans for the year ended December 31, 2021, is summarized as follows:

	Option Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of January 1, 2021		180,000		$	4.00
Exercised		(150,000	)		4.00
Forfeited or expired		—			—
Outstanding as of December 31, 2021		30,000		$	4.00		0.64	$	495,900
Exercisable at December 31, 2021		30,000		$	4.00		0.64	$	495,900

A summary of the Company’s stock option activity for the years ended January 1, 2021, and December 27, 2019, was as follows:

	January 1, 2021				December 27, 2019
	Option Shares		Weighted Average Exercise Price		Option Shares			Weighted Average Exercise Price
Outstanding at beginning of year		180,000	$	4.00		180,167		$	4.00
Exercised		—		—		—			—
Forfeited or expired		—		—		(167	)		3.63
Outstanding at end of year		180,000	$	4.00		180,000		$	4.00
Exercisable at end of year		180,000	$	4.00		180,000		$	4.00

The intrinsic value of the options that were exercised in 2021 was $2.4 million.

	Number of SARs		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding as of January 1, 2021		2,916,563	$	4.00		1.10
Exercised		2,916,563	$	4.00		—
Expired		—		—		—
Outstanding as of December 31, 2021		—		—		—
Exercisable at December 31, 2021		—		—		—

The fair value of the SARs and stock options is estimated using the Black-Scholes option pricing valuation model. The determination of fair value is affected by the Company's stock price, expected stock price volatility, expected term of the award and the risk-free rate of interest.

Under the stock plans, participants may be granted restricted stock units, each of which represents a conditional right to receive a common share in the future. The restricted stock units granted under this plan generally vest over one of the following vesting schedules: (1) a four -year period, with 50% vesting on the second anniversary and 25% of the shares vesting on the third and fourth anniversaries of the grant date, (2) a four -year period, with 25% vesting on the first, second, third and fourth anniversary, (3) a three -year period with 33% vesting on the first, second and third anniversary, or (4) a one-year period with 100% vest on the first anniversary. Upon vesting, the restricted stock units will convert into an equivalent number of shares of common stock. The amount of expense relating to the restricted stock units is based on the closing market price of the Company’s common stock on the date of grant and is amortized on a straight-line basis over the applicable requisite service period. Restricted stock unit activity for the year ended December 31, 2021, was as follows:

	Number of Restricted Stock Units			Weighted Average Grant-Date Fair Value
Nonvested balance as of January 1, 2021		1,191,504			16.47
Granted		516,224			15.16
Vested		(467,042	)		16.51
Forfeited		(65,520	)		15.94
Nonvested balance as of December 31, 2021		1,175,166		$	15.89

The Company recorded restricted stock units-based compensation expense of $9.7 million, $8.7 million and $6.8 million in 2021, 2020, and 2019 respectively, which is included in stock compensation expense, based on the vesting provisions of the restricted stock units and the fair value of the stock on the grant date. As of December 31, 2021, there was $9.2 million of total restricted stock unit compensation expense related to the unvested awards not yet recognized, which is expected to be recognized over a weighted average period of 2.2 years. The Company accounts for certain restricted stock units under liability accounting as a result of the fixed monetary amount and a variable number of shares that will be issued.

Shares of common stock subject to vesting requirements were issued to employees of acquired companies. These shares vest over a period of up to four years. Compensation expense was based on the fair value of the Company’s common stock at the time of grant and is recognized on a straight-line basis. The activity for common stock subject to vesting requirements for the year ended December 31, 2021, was as follows:

	Number of Shares of Common Stock Subject to Vesting Requirements			Weighted Average Grant-Date Fair Value
Nonvested balance as of January 1, 2021		67,151		$	18.51
Vested		(57,779	)		18.86
Forfeited		(6,427	)		16.26
Nonvested balance as of December 31, 2021		2,945		$	16.17

Common stock subject to vesting requirements of $1.0 million was issued in 2019 in relation to acquisitions. These shares are subject to up to a four-year vesting period.

The Company recorded compensation expense of $0.4 million, $1.1 million and $1.0 million, during the years ended December 31, 2021, January 1, 2021, and December 27, 2019, respectively, related to common stock subject to vesting requirements.

As of December 31, 2021, there was $27 thousand of total stock-based compensation expense related to common stock granted subject to vesting requirements not yet recognized, which is expected to be recognized over a weighted average period of 1.8 years.