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. Following amendments to the 2013 Omnibus Plan to reflect the effect of the Spin-Off and the November 2017 1-for-4 reverse stock split, 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 2013 Omnibus Plan provides for, and the 2003 Stock Plan provided for, both short-term and long-term incentive awards for employees, and the 2013 Omnibus Plan also provides for granting of long-term incentive awards for non-employee members of the Board of Directors. Options granted prior to 2011 are all exercisable and expire ten years subsequent to the grant date. Option grants to employees beginning in 2011 became exercisable in 25% increments beginning on the first anniversary of the grant date over a four-year period and expire ten years subsequent to the grant date. Beginning in 2017, grants to officers and directors 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. Restrictions on restricted stock awards and restricted stock units granted to employees lapse 100% on the third anniversary of the grant date. Restrictions on restricted stock units granted to non-employee members of the Board of Directors lapse 100% on the second anniversary of the grant date. Beginning in 2018, restrictions on restricted stock units granted to non-employee members of the Board of Directors lapse 100% on the grant date. Performance shares are earned based on the extent to which performance goals are met over the applicable performance period. The performance goals and the applicable performance period vary for each grant year. An explanation of the performance goals and the applicable performance period for the 2018, 2017 and 2016 awards are set forth below.

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 $7.5 million, $6.3 million and $4.9 million during 2018, 2017 and 2016, respectively. In 2018, the Company also recognized $0.7 million of expense before income tax related to the modification of stock awards associated with employee severance which is included in “restructuring expense” within operating earnings in the Consolidated Statements of Operations. In 2017, the Company also recognized $0.1 million of expense before income tax related to restricted stock retention awards and modification of performance awards due to the Spin-Off, and $0.6 million of expense before income tax related to the modification of stock awards associated with employee severance; these expenses are included in “other expense” and “restructuring expense,” respectively, within operating earnings in the Consolidated Statements of Operations In 2016, the Company also recognized $2.8 million of expense before income tax related to restricted stock retention awards and modification of performance awards due to the Spin-Off, and $1.3 million of expense before income tax related to the modification of stock awards associated with employee severance; these expenses are included in “other expense” and “restructuring expense,” respectively, within operating earnings in the Consolidated Statements of Operations. The Company recognized stock-based compensation expense before tax of $0.0 million, $0.0 million and $0.3 million during 2018, 2017 and 2016, respectively, related to MFS which is included in “(loss) income from discontinued operations” in the Consolidated Statements of Operations.

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

Any option grants to directors are exercisable immediately upon granting and expire ten years subsequent to the grant date. Prior to 2017, unvested stock option grants to officers and directors become exercisable in 25% increments annually over a four-year period beginning on the first anniversary of the grant date and expire ten years subsequent to the grant date. Beginning in 2017, grants to officers and directors are exercisable in three annual increments over a three-year period beginning on the first anniversary of the date and expire 10 years subsequent to the grant date.

The Company granted options to acquire 187,484, 273,800 and 439,741 shares of common stock during 2018, 2017 and 2016, respectively. Stock-based compensation expense is calculated by estimating the fair value of incentive and non-qualified stock options at the time of grant and is amortized over the stock options’ vesting period. The Company recognized $2.4 million, $1.9 million and $1.8 million of expense before income taxes associated with stock options during 2018, 2017 and 2016, respectively.

	Shares			Weighted Average Exercise Price Per Share		Aggregate Intrinsic Value
Options outstanding as of January 1, 2017		966,060		$	17.78
Granted		273,800			25.68
Exercised		(258,699	)		19.86
Forfeited		(80,727	)		20.45
Cancelled		(24,287	)		26.98
Options outstanding as of December 31, 2017		876,147			19.13
Granted		187,484			32.31
Exercised		(96,125	)		19.81
Forfeited		(5,215	)		25.44
Cancelled		(5,931	)		24.36
Options outstanding as of December 31, 2018		956,360		$	21.57	$	0.6
Options exercisable as of:
December 31, 2018		511,899		$	17.98	$	0.6

The Company uses the Black-Scholes valuation model to value stock options. The Company used its historical stock prices as the basis for its volatility assumption for grants prior to the Spin-Off. For grants after the Spin-Off, the Company used an average of historical stock prices of selected peers. 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, 2018, 2017 and 2016 was $15.66, $12.16 and $8.20, respectively. The fair value of each option grant was estimated at the date of grant using the Black-Scholes option-pricing method with the following assumptions:

	2018			2017			2016
Expected Life (years)		6.5			6.5			6.5
Risk-free Interest rate		2.8	%		2.2	%		1.6	%
Expected volatility		43.7	%		45.0	%		45.0	%
Expected dividend yield		—	%		—	%		—	%

As of December 31, 2018, the Company has $3.4 million of unrecognized compensation expense before income tax related to stock options, which will be recognized over a weighted average period of 1.7 years.

For the years ended December 31, 2018, 2017 and 2016, the total intrinsic value of stock options exercised was $1.1 million, $3.0 million and $6.3 million, respectively.

The Company granted 80,548 restricted stock awards to certain employees in 2015 as retention awards to provide incentive for the employees to continue in employment and contribute toward the successful completion of the Spin-Off. Under the retention agreements, the restricted stock awards vested on the second anniversary of the Spin-Off if the employee had been continuously employed with the Company or an affiliate through that second anniversary.

The Company recognized an immaterial amount of compensation expense associated with the restricted stock awards for the years ended December 31, 2018 and 2017. For the year ended December 31, 2016 the Company recognized $1.8 million of compensation expense associated with restricted stock awards. Restricted stock award expense is based on the fair value of the Company’s shares as of the grant date.

A summary of activity for restricted stock awards for the years ended December 31, 2018 and 2017 are as follows:

	Shares			Weighted Average Grant Date Fair Value Per Share
Unvested as of January 1, 2017		39,028		$	86.92
Granted		—			—
Vested		(11,058	)		86.92
Forfeited		(5,546	)		86.92
Unvested as of December 31, 2017		22,424			86.92
Granted		—			—
Vested		(22,424	)		86.92
Forfeited		—			—
Unvested as of December 31, 2018		—		$	—

As of December 31, 2018, the Company has zero of unrecognized compensation expense before income tax related to restricted stock awards.

The Company granted 111,713, 152,855 and 157,402 restricted stock units in 2018, 2017 and 2016, respectively. The restricted stock units are earned based on service over the vesting period. The Company recognized $2.6 million, $3.1 million and $0.4 million of compensation expense associated with restricted stock units during 2018, 2017 and 2016, respectively.

The restricted stock units granted to employees in 2018 generally vest on the third anniversary of the grant date, assuming continued employment. The restricted stock units granted to directors in 2018 vest immediately on the grant date. The expense is based on the fair value of the Company's shares as of the grant date.

The restricted stock units granted to employees in 2017 and 2016 generally vest on the third anniversary of the grant date, assuming continued employment. The restricted stock units granted to directors in 2017 and 2016 vest on the second anniversary of the grant date, assuming continued service. The expense is based on the fair value of the Company's shares as of the grant date.

A summary of activity for restricted stock units for the years ended December 31, 2018 and 2017 are as follows:

	Shares			Weighted Average Grant Date Fair Value Per Share
Unvested as of January 1, 2017		241,108		$	49.03
Granted		152,855			26.05
Vested		(45,755	)		93.55
Forfeited		(28,208	)		35.61
Unvested as of December 31, 2017		320,000			32.71
Granted		111,713			28.49
Vested		(203,355	)		38.81
Forfeited		(8,869	)		21.04
Unvested as of December 31, 2018		219,489		$	25.37

As of December 31, 2018, the Company has $3.0 million of unrecognized compensation expense before income tax related to restricted stock units which will be recognized over a weighted average period of 1.9 years.

The Company granted 93,298, 115,047 and 204,891 of performance stock units in 2018, 2017 and 2016, 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 $2.5 million, $1.3 million and $1.8 million of compensation expense associated with performance stock units during 2018, 2017 and 2016, respectively.

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 number of shares awarded could range from zero to 185,184. The expense is based on the fair value of the Company's shares as of the grant date for the adjusted EBITDA margin criteria and a Monte Carlo valuation model for the total shareholder return criteria.

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. Depending on the foregoing factors, the number of shares awarded could range from zero to 196,316. The expense is based on the fair value of the Company's shares as of the grant date for the adjusted EBITDA margin criteria and a Monte Carlo valuation model for the total shareholder return criteria.

The performance stock units granted in 2016 are earned based on the extent to which performance goals are met by the Company over a three-year period from January 1, 2016 to December 31, 2018. 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 return on invested capital over the three-year period. At the end of the performance period, approximately 75,000 shares will be awarded and will vest on the grant date of the awards. The expense is based on the fair value of the Company's shares as of the grant date for the return on invested capital criteria and a Monte Carlo valuation model for the total shareholder return criteria.

A summary of activity for performance stock units for the years ended December 31, 2018 and 2017 are as follows:

	Shares			Weighted Average Grant Date Per Share
Unvested as of January 1, 2017		201,257		$	28.45
Granted		115,047			30.58
Vested		(17,637	)		85.03
Forfeited		(29,425	)		25.59
Unvested as of December 31, 2017		269,242			25.97
Granted		93,298			33.86
Vested		—			—
Forfeited		(3,675	)		30.31
Unvested as of December 31, 2018		358,865		$	27.98

As of December 31, 2018, the Company has $3.1 million of unrecognized compensation expense before income tax related to performance stock units which will be recognized over a weighted average period of 1.8 years.