Total share-based compensation included in net income for the years ended December 28, 2018, December 29, 2017, and December 30, 2016 is as follows:

	Year Ended
	December 28,		December 29,		December 30,
	2018		2017		2016
Restricted stock units	$	7,283	$	7,801	$	7,550
Stock options and stock appreciation rights		—		—		—
Common stock subject to vesting requirements		2,027		2,515		1,215
	$	9,310	$	10,316	$	8,765

The number of shares available for future issuance under the Company's stock plans as of December 28, 2018 were 1,798,440. 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 market 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 28, 2018 is summarized as follows:

	Option Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding as of December 29, 2017		180,167	$	4.00
Exercised		—		—
Forfeited or expired		—		—
Outstanding as of December 28, 2018		180,167	$	4.00		3.22	$	2,147,591
Exercisable at December 28, 2018		180,167	$	4.00		3.22	$	2,147,591

A summary of the Company’s stock option activity for the years ended December 29, 2017 and December 30, 2016 was as follows:

	December 29, 2017					December 30, 2016
	Option Shares			Weighted Average Exercise Price		Option Shares		Weighted Average Exercise Price
Outstanding at beginning of year		230,167		$	4.00		230,167		4.00
Exercised		(50,000	)		4.00		—		—
Forfeited or expired		—			—		—		—
Outstanding at end of year		180,167		$	4.00		230,167	$	4.00
Exercisable at end of year		180,167		$	4.00		230,167	$	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 28, 2018, December 29, 2017, and December 30, 2016 was as follows (in thousands):

	Year Ended
	December 28, 2018		December 29, 2017		December 30, 2016
Total intrinsic value of stock options exercised	$	—	$	803	$	—

	Number of SARs		Weighted Average Exercise Price		Weighted Average Fair Value
Outstanding as of December 29, 2017		2,916,563	$	4.00		1.31
Granted/Expired/Forfeited		—		—		—
Outstanding as of December 28, 2018		2,916,563	$	4.00	$	1.31
Exercisable at December 28, 2018		2,916,563	$	4.00	$	1.31

The following assumptions were used to determine the fair value of the SARs granted to employees:

In March 2013, the Company’s Chief Executive Officer and Chief Financial Officer received SARs totaling 2,916,563 after surrendering their performance-based stock option grants. As of December 28, 2018, no SARs had been exercised.

As of December 28, 2018, all of the outstanding options and SARs were performance-based. As of January 1, 2016, all stock compensation expense related to the outstanding options and SARs had been expensed.

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 28, 2018, was as follows:

	Number of Restricted Stock Units			Weighted Average Grant-Date Fair Value
Nonvested balance as of December 29, 2017		1,519,638			12.96
Granted		460,910			16.74
Vested		(804,065	)		10.66
Forfeited		(29,792	)		15.42
Nonvested balance as of December 28, 2018		1,146,691		$	15.93

The Company recorded restricted stock units based compensation expense of $7.3 million, $7.8 million and $7.6 million in 2018, 2017, and 2016, respectively, which is included in stock compensation expense, based on the vesting provisions of the restricted stock units and the fair market value of the stock on the grant date. As of December 28, 2018, there was $8.9 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 2.5 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. See Note 5 for further details.

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 market 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 28, 2018 was as follows:

	Number of Shares of Common Stock Subject to Vesting Requirements			Weighted Average Grant-Date Fair Value
Nonvested balance as of December 29, 2017		431,024		$	13.52
Granted		7,728			16.01
Vested		(148,589	)		8.73
Forfeited		(656	)		19.82
Nonvested balance as of December 28, 2018		289,507		$	16.03

Common stock subject to vesting requirements of $0.1 million and $3.6 million was issued in 2018 and 2017, respectively, in relation to the equity portion of the Jibe acquisition closing consideration and the Technolab earn-out consideration, respectively. These shares are subject to a four year vesting period.

The Company recorded compensation expense of $2.0 million, $2.5 million and $1.2 million, during the years ended December 28, 2018, December 29, 2017, and December 30, 2016, respectively, related to common stock subject to vesting requirements.

As of December 28, 2018, there was $2.2 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 2.2 years.