The Company’s 2013 Omnibus Incentive Plan (the “2013 Omnibus Plan”) was approved by shareholders on May 7, 2013 and replaced the 2003 Incentive Stock and Awards Plan (the “2003 Stock Plan”). The 2013 Omnibus Plan also replaced the Company’s Short-Term Incentive Plan (the “STIP”) as of December 31, 2013. The 2003 Stock Plan and the STIP are referred to cumulatively as the “Prior Plans.” No new awards may be granted under the Prior Plans after the respective termination dates, but the Prior Plans continue to govern awards outstanding issued thereunder; outstanding awards will continue in force and effect until vested, exercised or forfeited pursuant to their terms. The 2013 Omnibus Plan provides for both short-term and long-term incentive awards for employees and non-employee directors. Stock-based awards may take the form of stock options, stock appreciation rights, restricted stock, restricted stock units, and performance share or performance unit awards. The total number of shares of the Company’s common stock available for awards under the 2013 Omnibus Plan is 7,477,395 shares. The total number of shares of the Company’s common stock still available for issuance as of December 31, 2019 is 4,992,222 shares.

The Company recognizes expense for all stock-based compensation on a straight-line basis over the vesting period of the entire award.

Total stock-based compensation expense recognized within engineering, selling and administrative expenses in the Consolidated Statements of Operations was $9.5 million, $7.5 million and $6.3 million during the years ended December 31, 2019, 2018 and 2017, respectively. In 2018 and 2017, the Company recognized $0.7 million and $0.6 million, respectively, of expense related to the modification of stock awards associated with employee severance which is included in restructuring expense in the Consolidated Statements of Operations. In 2017, the Company also recognized $0.1 million of expense related to restricted stock retention awards and modification of performance awards due to the spin-off of the former food service business in other income (expense) – net in the Consolidated Statements of Operations.

Shares are issued out of treasury stock upon exercise for stock options and vesting of restricted stock units and performance stock units.

Beginning in 2017, stock option grants to employees are exercisable in three annual increments over a three-year period beginning on the first anniversary of the grant date and expire 10 years subsequent to the grant date.

The Company granted stock options to employees to acquire 210,243, 187,484 and 273,800 shares of common stock during the years ended December 31, 2019, 2018 and 2017, respectively. Stock-based compensation expense is calculated by estimating the fair value of non-qualified stock options at the time of grant and is amortized over the stock options’ vesting period. The Company recognized $2.7 million, $2.4 million and $1.9 million of expense before income taxes associated with stock options during 2019, 2018 and 2017, respectively.

	Shares			Weighted Average Exercise Price Per Share		Aggregate Intrinsic Value
Options outstanding as of December 31, 2018		956,164			21.58
Granted		210,243			18.40
Exercised		(58,404	)		6.57
Forfeited		(17,164	)		23.81
Cancelled		(24,868	)		21.18
Options outstanding as of December 31, 2019		1,065,971		$	21.75	$	0.4

Options exercisable as of December 31, 2019		623,487		$	20.96	$	0.4

The Company uses the Black-Scholes valuation model to value stock options. The Company used an average of historical stock prices of selected peers for its volatility assumption. The assumed risk-free rates were based on ten-year U.S. Treasury rates in effect at the time of grant. The expected option life represents the period of time that the options granted are expected to be outstanding and is based on historical experience.

The weighted average fair value of options granted per share during the years ended December 31, 2019, 2018 and 2017 was $8.07, $15.66 and $12.16, respectively. The fair value of each option grant was estimated at the date of grant using the following assumptions:

	2019			2018			2017
Expected life (years)		6.5			6.5			6.5
Risk-free interest rate		2.6	%		2.8	%		2.2	%
Expected volatility		39.8	%		43.7	%		45.0	%
Expected dividend yield		—	%		—	%		—	%

As of December 31, 2019, the Company has $2.3 million of unrecognized compensation expense before income tax related to stock options, which will be recognized over a weighted average period of 1.3 years.

For the years ended December 31, 2019, 2018 and 2017, the total intrinsic value of stock options exercised was $0.5 million, $1.1 million and $3.0 million, respectively.

The Company granted 229,044, 111,713 and 152,855 restricted stock units in 2019, 2018 and 2017, respectively, which also includes equity grants to non-employee directors of 50,673, 25,021 and 33,208 in 2019, 2018, and 2017, respectively. The Company recognized $3.4 million, $2.6 million and $3.1 million of compensation expense associated with restricted stock units during 2019, 2018 and 2017, respectively.

date, assuming continued employment. The expense is based on the fair value of the Company's shares as of the grant date which, for restricted stock units, is the grant date closing stock price.

	Shares			Weighted Average Grant Date Fair Value Per Share
Unvested as of December 31, 2018		219,917			25.37
Granted		229,044			18.39
Vested		(154,295	)		20.26
Forfeited		(4,103	)		27.34
Unvested as of December 31, 2019		290,563		$	22.55

As of December 31, 2019, the Company has $3.7 million of unrecognized compensation expense before income tax related to restricted stock units which will be recognized over a weighted average period of 1.6 years.

The Company granted 228,037, 93,298 and 115,047 of performance stock units in 2019, 2018 and 2017, respectively. The performance stock units are earned based on service over the vesting period and on the extent to which performance goals are met over the applicable three-year performance period. The performance goals vary for performance shares each grant year. The Company recognized $3.4 million, $2.5 million and $1.3 million of compensation expense associated with performance stock units during 2019, 2018 and 2017, respectively.

The performance stock units granted in 2019 are earned based on the extent to which performance goals are met by the Company over a three-year period from January 1, 2019 to December 31, 2021. The performance goals were based fifty percent (50%) on total shareholder return relative to a peer group of companies over the three-year period and fifty percent (50%) on meeting targeted adjusted EBITDA margin at the end of the three-year period. Depending on the foregoing factors, the current number of shares awarded could range from zero to 452,890.

The performance stock units granted in 2018 are earned based on the extent to which performance goals are met by the Company over a three-year period from January 1, 2018 to December 31, 2020. The performance goals were based fifty percent (50%) on total shareholder return relative to a peer group of companies over the three-year period and fifty percent (50%) on meeting targeted adjusted EBITDA margin at the end of the three-year period. Depending on the foregoing factors, the current number of shares awarded could range from zero to 179,770.

The performance stock units granted in 2017 are earned based on the extent to which performance goals are met by the Company over a three-year period from January 1, 2017 to December 31, 2019. The performance goals were based fifty percent (50%) on total shareholder return relative to a peer group of companies over the three-year period and fifty percent (50%) on meeting targeted adjusted EBITDA margin at the end of the three-year period. Excluding potential forfeitures, the Company expects to issue 87,642 shares of common stock in 2020 related to these awards.

	Shares			Weighted Average Grant Date Fair Value Per Share
Unvested as of December 31, 2018		337,124			28.02
Granted		228,037			22.01
Vested		(74,315	)		25.73
Forfeited		(78,441	)		20.24
Unvested as of December 31, 2019		412,405		$	26.58

As of December 31, 2019, the Company has $4.3 million of unrecognized compensation expense before income tax related to performance stock units which will be recognized over a weighted average period of 2.0 years.

The expense for the adjusted EBITDA performance stock units is based on the fair value of the Company's shares as of the grant date which is the grant date closing stock price. For total shareholder return performance stock units, the Company uses the Monte Carlo valuation model to determine fair value of the grants. The Company used an average of historical stock prices of selected peers for its volatility assumption. The assumed risk-free rates were based on three-year U.S. Treasury rates in effect at the time of grant. The fair value of each total shareholder return performance stock unit was estimated at the date of grant using the following assumptions:

	2019			2018			2017
Correlation		32.5	%		29.5	%		31.6	%
Risk-free interest rate		2.5	%		2.4	%		1.5	%
Expected volatility		47.0	%		33.8	%		35.0	%
Expected dividend yield		—	%		—	%		—	%