Total share-based compensation included in net income for the years ended December 27, 2019, December 28, 2018 and December 29, 2017, is as follows:

	Year Ended
	December 27,		December 28,		December 29,
	2019		2018		2017
Restricted stock units	$	6,762	$	7,283	$	7,801
Stock options and stock appreciation rights		—		—		—
Common stock subject to vesting requirements		954		2,027		2,515
	$	7,716	$	9,310	$	10,316

The number of shares available for future issuance under the Company's stock plans as of December 27, 2019 were 1,466,084. 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 27, 2019 is summarized as follows:

	Option Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 28, 2018		180,167		$	4.00
Exercised		—			—
Forfeited or expired		(167	)		3.63
Outstanding as of December 27, 2019		180,000		$	4.00		2.23	$	2,142,000
Exercisable at December 27, 2019		180,000		$	4.00		2.23	$	2,142,000

A summary of the Company’s stock option activity for the years ended December 28, 2018 and December 29, 2017, was as follows:

	December 28, 2018				December 29, 2017
	Option Shares		Weighted Average Exercise Price		Option Shares			Weighted Average Exercise Price
Outstanding at beginning of year		180,167	$	4.00		230,167			4.00
Exercised		—		—		(50,000	)		4.00
Forfeited or expired		—		—		—			—
Outstanding at end of year		180,167	$	4.00		180,167		$	4.00
Exercisable at end of year		180,167	$	4.00		180,167		$	4.00

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.

Other information pertaining to stock option activity during the years ended December 27, 2019, December 28, 2018 and December 29, 2017, was as follows (in thousands):

	Year Ended
	December 27, 2019		December 28, 2018		December 29, 2017
Total intrinsic value of stock options exercised	$	—	$	—	$	803

	Number of SARs		Weighted Average Exercise Price		Weighted Average Fair Value
Outstanding as of December 28, 2018		2,916,563	$	4.00		1.31
Expired		—		—		—
Outstanding as of December 27, 2019		2,916,563	$	4.00	$	1.31
Exercisable at December 27, 2019		2,916,563	$	4.00	$	1.31

As of December 27, 2019, no SARs had been exercised and all of the outstanding options and SARs were performance-based .

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, or (3) a three -year period with 33% vesting on the first, second and third 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 27, 2019, was as follows:

	Number of Restricted Stock Units			Weighted Average Grant-Date Fair Value
Nonvested balance as of December 28, 2018		1,146,691			15.93
Granted		542,455			18.05
Vested		(436,671	)		14.91
Forfeited		(209,932	)		15.13
Nonvested balance as of December 27, 2019		1,042,543		$	17.34

The Company recorded restricted stock units based compensation expense of $6.8 million, $7.3 million and $7.8 million in 2019, 2018 and 2017, 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 27, 2019, there was $10.4 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 2.4 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 27, 2019 was as follows:

	Number of Shares of Common Stock Subject to Vesting Requirements			Weighted Average Grant-Date Fair Value
Nonvested balance as of December 28, 2018		289,507		$	16.03
Granted		81,423			15.94
Vested		(211,567	)		14.31
Forfeited		(30,572	)		16.67
Nonvested balance as of December 27, 2019		128,791		$	18.64

Common stock subject to vesting requirements of $1.0 million and $0.1 million was issued in 2019 and 2018, respectively, in relation to the equity portion of the Jibe, Aecus and Technolab acquisitions. These shares are subject to a four-year vesting period.

The Company recorded compensation expense of $1.0 million, $2.0 million and $2.5 million, during the years ended December 27, 2019, December 28, 2018 and December 29, 2017, respectively, related to common stock subject to vesting requirements.

As of December 27, 2019, there was $1.6 million 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 1.7 years.