The Company's 2015 Stock Incentive Plan (the "2015 Plan"), which provides for share-based awards to Company employees, non-employee directors and outside consultants or advisors, was approved by stockholders on May 27, 2015. The number of shares of common stock reserved for issuance under the 2015 Plan is 1,000,000, of which the maximum number of shares for which incentive stock options may be granted is 900,000. The 2015 Plan replaced the Company’s 2009 Stock Incentive Plan (the “2009 Plan”), and no new share-based awards may be granted under the 2009 Plan. The number of shares available for grant at December 31, 2018 is 506,295. Outstanding option awards under all the plans generally expire ten years after the date of grant.

Share-based compensation expense included in selling, general and administrative expenses during the years ended December 31, 2018, 2017 and 2016, was $5.5 million, $4.2 million and $2.8 million, respectively. Related income tax benefits for the years ended December 31, 2018, 2017 and 2016, were $1.5 million, $1.5 million and $1.1 million, respectively.

Stock options are generally exercisable in four equal annual installments beginning one year following the date of grant.

A summary of the status of the Company’s stock options at December 31, 2018, together with changes during the periods then ended, is presented below:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Number			Exercise		Contractual		Value
	of Options			Price		Term (Years)		(In Thousands)
Outstanding at December 31, 2017		292,400		$	17.99		—		—
Options granted at market price		120,000			82.21		—		—
Options exercised		(40,140	)		14.39		—		—
Outstanding at December 31, 2018		372,260			39.08		4.86		9,759
Exercisable at December 31, 2018		219,135			17.73		2.56	$	8,661

The fair value of stock option awards as determined under the Black-Scholes option-pricing model was estimated with the following weighted-average assumptions:

	2018			2016
Expected volatility		42.2	%		55.2		%
Risk free interest rate		2.7	%		1.2		%
Expected dividend yield		1.2	%		2.2		%
Expected term		8.3 years			6.2 years
Weighted average fair value per share	$	36.41		$		17.10

The weighted average fair value of stock options granted for the years ended December 31, 2018 and 2016 was $36.41 and $17.10, respectively. There were no stock options granted with an exercise price below market price during 2018 and 2016. No stock options were granted during 2017.

The intrinsic value of stock options exercised for the years ended December 31, 2018, 2017 and 2016 was $2.5 million, $479,000 and $113,000, respectively. The fair value of stock options vested for the years ended December 31, 2018, 2017 and 2016 was $312,000, $328,000 and $319,000, respectively. As of December 31, 2018, unrecognized compensation expense related to stock options was $4.3 million with a weighted average remaining amortization period of 7.1 years.

Restricted stock units generally vest in four equal annual installments beginning one year following the date of grant.

				Weighted Average
				Grant Date
	Units			Fair Value
Nonvested at December 31, 2017		234,383		$	47.26
Granted		55,352			96.31
Vested		(53,938	)		46.56
Cancelled/Forfeited		(31,943	)		46.20
Nonvested at December 31, 2018		203,854		$	60.93

The total fair value of restricted stock units vested during the years ended December 31, 2018, 2017 and 2016 was $4.0 million, $3.3 million and $1.9 million, respectively. As of December 31, 2018, unrecognized compensation expense related to restricted stock units was $10.1 million with a weighted average remaining amortization period of 2.6 years.