SHARE BASED AWARDS

We have a stock incentive plan for employees and directors and an employee stock purchase plan. Shares to be issued under these plans will be issued either from authorized but unissued shares or from treasury shares.

We incur stock compensation expense for stock options, restricted stock units ("RSU"), performance restricted stock units ("PRSU") and stock purchased under our employee stock purchase plan ("ESPP"). We receive a tax benefit on stock compensation expense and direct tax benefits from the exercise of stock options. We also have indirect tax benefits upon exercise of stock options related to research and development tax credits which are recorded as a reduction of income tax expense. The table below summarizes compensation costs and related tax benefits (in thousands):



	Year ended December 31,
(In thousands)	2017		2016		2015
Stock compensation expense	$	19,352	$	15,242	$	12,827
Tax benefit from stock-based compensation cost	$	7,247	$	5,682	$	4,922
Indirect tax benefit	$	1,374	$	—	$	1,997

As of December 31, 2017, we had $23.3 million of unamortized stock compensation cost which we will recognize as an expense over approximately 0.8 years.

Stock Incentive and Stock Option Plans

Our 2011 Stock Incentive Plan ("2011 Plan") replaced our 2003 Stock Option Plan (“2003 Plan”). Our 2011 Plan initially had 650,000 shares available for issuance, plus the remaining available shares for grant from the 2003 Plan. In 2012, 2014 and 2017, our stockholders approved amendments to the 2011 plan that increased the shares available for issuance by 3,275,000, bringing the initial shares available for issuance to 3,925,000, plus the remaining 248,700 shares that remained available for grant from the 2003 Plan. In addition, any forfeited, terminated or expired shares that would otherwise return to the 2003 Plan are available under the 2011 Plan. As of December 31, 2017, the 2011 Plan has 4,188,300 shares of common stock reserved for issuance to employees, which includes 263,300 shares that transferred from the 2003 Plan. Shares issued as options or stock appreciation rights ("SARs") are charged against the 2011 Plan's share reserve as one share for one share issued. Shares subject to awards other than options and SARs are charged against the 2011 Plan's share reserve as 2.09 shares for 1 share issued. Options may be granted with exercise prices at no less than fair market value at date of grant. Options granted under the 2011 Plan may be “non-statutory stock options” which expire no more than ten years from date of grant or “incentive stock options” as defined in Section 422 of the Internal Revenue Code of 1986, as amended. Upon exercise of non-statutory stock options, we are generally entitled to a tax deduction on the exercise of the option for an amount equal to the excess over the exercise price of the fair market value of the shares at the date of exercise; we are generally not entitled to any tax deduction on the exercise of an incentive stock option. The 2011 Plan includes conditions whereby unvested options are cancelled if employment is terminated.

In 2014, our Compensation Committee of the Board of Directors awarded our then new Chief Executive Officer an employment inducement option to purchase 182,366 shares of our common stock and an employment inducement grant of restricted stock units with respect to 68,039 shares of our common stock. The inducement grants were made out of our 2014 Inducement Incentive Plan ("2014 Plan").

Our 2001 Directors’ Stock Option Plan (the “Directors’ Plan”), initially had 750,000 shares reserved for issuance to members of our Board of Directors, expired in November 2011. Although no new grants may be made under the Director's Plan, grants made under the Director's Plan prior to its expiration continue to remain outstanding. Options not vested terminate if the directorship is terminated.

Time-based Stock Options

To date, all options granted under the 2014 Plan, 2011 Plan, 2003 Plan and Directors' Plan have been non-statutory stock options. The majority of the time-based outstanding employee option grants vest 25% after one year from the grant date and the balance vests ratably on a monthly basis over 36 months. The majority of the outstanding options granted to non-employee directors vest one year from the grant date. The options generally expire 10 years from the grant date.

The fair value of time-based option grants is calculated using the Black-Scholes option valuation model. The expected term for the option grants was based on historical experience and expected future employee behavior. We estimate the volatility of our common stock at the date of grant based on the historical volatility of our common stock, based on the average expected exercise term. The table below summarizes the total time-based stock options granted, total valuation and the weighted average assumptions (dollars in thousands):



	Year ended December 31,
	2017			2016			2015
Number of time-based options granted	8,825			13,405			22,816
Grant date fair value of options granted (in thousands)	$	375		$	413		$	590
Weighted average assumptions for stock option valuation:
Expected term (years)	5.5			5.5			5.6
Expected stock price volatility	27.0		%	31.8		%	25.9		%
Risk-free interest rate	1.1		%	0.7		%	1.7		%
Expected dividend yield	—		%	—		%	—		%
Weighted average grant price per option	$	158.20		$	101.32		$	93.30
Weighted average grant date fair value per option	$	42.51		$	30.78		$	25.86

Performance Stock Options

In 2015, we granted performance stock option grants which are exercisable if the common stock price condition and the time-based vesting have been met. The 2015 performance based stock option grants vest ratably at 33% per year over three years. For the 2015 grants, the vested performance stock options became exercisable when the closing price of our common stock was equal to or more than 130% of the exercise price for 30 consecutive trading days during the term of the grant. All of the 2015 performance stock option grant's common stock price conditions have been met.

The fair value of performance option grants is calculated using the Monte Carlo Simulation. The expected term of the performance option grants is based on the expected number of years to achieve the exercisable goal trigger and assumes that the vested option will be immediately exercised or cancelled, if underwater. We estimate the volatility of our common stock at the date of grant based on the historical volatility of our common stock over a 10-year period.

The table below summarizes the performance stock options granted, the total valuation and the weighted average assumptions (dollars in thousands). There were no performance option grants in 2017 or 2016.



	Year ended December 31,
	2017	2016	2015
Number of performance options granted			244,825
Number of performance options earned		244,825	349,812
Grant date fair value of options granted (in thousands)			$	6,087
Weighted average assumptions for stock option valuation:
Expected term (years)			3.0
Expected stock price volatility			30.86		%
Risk-free interest rate			2.3		%
Expected dividend yield			—		%
Weighted average grant price per option			$	91.88
Weighted average grant date fair value per option			$	24.86

A summary of our stock option activity as of and for the year ended December 31, 2017 is as follows:



	Shares		Weighted Average Exercise Price Per Share		Weighted Average Contractual Life (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	2,018,290		$	58.90
Granted	8,825		$	158.20
Exercised	(610,316	)	$	52.43
Forfeited or expired	(72	)	$	58.79
Outstanding at December 31, 2017	1,416,727		$	62.30	5.8	$	217,749
Exercisable at December 31, 2017	1,133,734		$	60.13	5.6	$	176,721
Vested and expected to vest, December 31, 2017	1,416,727		$	62.30	5.8	$	217,749

The intrinsic values for options exercisable, outstanding and vested or expected to vest at December 31, 2017 is based on our closing stock price of $216.00 at December 31, 2017 and are before applicable taxes.



	Year ended December 31,
(In thousands)	2017		2016		2015
Intrinsic value of options exercised	$	71,283	$	25,065	$	28,071
Cash received from exercise of stock options	$	32,003	$	17,346	$	15,042
Tax benefit from stock option exercises	$	20,004	$	7,556	$	9,330

Stock Awards

In 2017, we granted performance restricted stock units ("PRSU") to our executive officers. The PRSUs will vest, if at all, upon the achievement of a minimum Cumulative Adjusted EBITDA, subject to a three-year cliff vesting ending on December 31, 2019. If at that date, our Cumulative Adjusted EBITDA is at least $600 million but less than $650 million, 100% of the awarded units will vest. If our Cumulative Adjusted EBITDA is at least $650 million but less than $700 million, 200% of the awarded units will vest. If our Cumulative Adjusted EBITDA is at least $700 million, 300% of the awarded units will vest.

In 2016, we granted PRSUs to our executive officers, which will vest, if at all, upon the achievement of a minimum specified compound annual growth rate ("CAGR") in adjusted EBITDA per share, subject to a three-year cliff vesting ending on December 31, 2018. If at that date, our adjusted EBITDA per share CAGR is at least 8% but less than 10%, 100% of the awarded units will vest. If our adjusted EBITDA per share CAGR is at least 10% but less than 12%, 200% of the awarded units will vest. If our adjusted EBITDA per share CAGR is greater than 12%, 300% of the awarded units will vest. As of October 1, 2017 we expect our adjusted EBITDA per share CAGR to be greater than 12% at December 31, 2018.

Restricted stock units ("RSU") are granted annually to our Board of Directors and vest on the first anniversary of the grant date.

In 2017, 2016 and 2015, we granted RSUs to certain employees that vest ratably on the anniversary of the grant over three years. Additionally in 2015, we granted RSUs to certain new hire employees that vest ratably on the anniversary of the grant over two years.

The table below summarizes our restricted stock award activity (dollars in thousands):



	Year ended December 31,
(In thousands except shares and per share amounts)	2017		2016		2015
PRSU
Shares granted	20,686		36,370		—
Shares earned	—		—		—
Grant date fair value per share	$	154.75	$	86.47	$	—
Grant date fair value	$	3,201	$	3,145	$	—
Intrinsic value vested	$	—	$	—	$	787

RSU
Shares granted	107,678		60,377		67,745
Grant date fair value per share	$	156.49	$	87.47	$	93.52
Grant date fair value	$	16,851	$	5,281	$	6,336
Intrinsic value vested	$	9,813	$	4,680	$	2,754

The table below provides a summary of our PRSU and RSU activity as of and for the year ended December 31, 2017.



	Number of Units		Grant Date Fair Value Per Share		Weighted Average Contractual Life (Years)	Aggregate Intrinsic Value
Non-vested at December 31, 2016	159,439		$	84.68
Change in units due to performance expectations^(a)	72,740		$	86.47
Granted	128,364		$	156.21
Vested	(66,278	)	$	80.61
Forfeited	(8,762	)	$	148.76
Non-vested and expected to vest at December 31, 2017	285,503		$	116.28	1.0	$	33,197

(a) Relates to the 2016 PRSUs, assumes attainment of maximum payout rate as set forth in performance criteria.

ESPP

We have an ESPP under which U.S. employees may purchase up to $25,000 annually of common stock at 85% of its fair market value at the beginning or the end of a six-month offering period, whichever is lower. There are 750,000 shares of common stock reserved for issuance under the ESPP, which is subject to an annual increase of the least of 300,000 shares, two percent of the shares outstanding or such a number as determined by the Board. To date, there have been no increases. As of December 31, 2017, there were 133,487 shares available for future issuance. The ESPP is intended to constitute an “employee stock purchase plan” within the meaning of Section 423 of the Internal Revenue Code. During 2017, we suspended our ESPP.

The fair value of rights to purchase shares under the ESPP is calculated using the Black-Scholes option valuation model. The table below summarizes the number and intrinsic value of ESPP share purchases and the weighted average valuation assumptions for the 2017, 2016 and 2015 purchase periods.



	Year ended December 31,
	2017			2016			2015
ESPP shares purchased by employees	23,426			31,227			34,299
Intrinsic value of ESPP purchases (in thousands)	$	986		$	955		$	1,382
Weighted average assumptions for ESPP valuation:
Expected term (in years)	0.5			0.5			0.5
Expected stock price volatility	28.1		%	32.5		%	27.0		%
Risk-free interest rate	0.6		%	0.3		%	0.6		%
Expected dividend yield	—		%	—		%	—		%