6. Stockholders’ Equity

Stock Options

The Company uses the Black-Scholes option pricing model for determining the estimated fair value for stock-based awards. The weighted-average assumptions used in the Black-Scholes option pricing model are as follows:

	Three Months Ended March 31,
	2013		2012
Expected stock price volatility	66	%	69	%
Risk-free interest rate	0.85	%	0.89	%
Expected life of options (in years)	4.49		4.56
Expected dividend yield	0	%	0	%

The weighted-average fair value (as of the date of grant) of the options was $15.71 and $16.55 per share for the three months ended March 31, 2013 and 2012, respectively. During the three months ended March 31, 2013 and 2012, the Company recorded total pre-tax stock-based compensation expense of $4.9 million ($3.3 million after tax or $0.09 per diluted share) and $5.2 million ($3.4 million after tax or $0.09 per diluted share), respectively, which includes the fair value for equity awards issued after January 1, 2006. The total stock-based compensation cost related to non-vested equity awards not yet recognized as an expense as of March 31, 2013 was approximately $39.9 million. That cost is expected to be recognized over a weighted-average period of approximately 2.62 years.

The following table summarizes information about shares available for grant and stock options outstanding as of March 31, 2013:

					Weighted-
					Average
			Weighted-		Remaining	Aggregate
	Number of		Average		Contractual	Intrinsic
Options	Options		Exercise Price		Term (Years)	Value
Outstanding at December 31, 2012	3,976		$	20.88
Options Granted	358		29.85
Options Exercised	(398	)	15.62
Options Cancelled	(85	)	23.57
Outstanding at March 31, 2013	3,851		$	22.19	4.81	$	35,534
Vested or expected to vest at March 31, 2013	3,662		$	21.93	4.74	$	34,846
Exercisable at March 31, 2013	2,302		$	19.75	4.09	$	27,451

A summary of the Company’s non-vested restricted stock at March 31, 2013, and changes during the three months ended March 31, 2013, is presented below:

Non-Vested Restricted Stock	Number of Awards
Non-vested at December 31, 2012	866
Granted	523
Vested	(136	)
Forfeited	(58	)
Non-vested at March 31, 2013	1,195

Employee Stock Purchase Plan

On February 1, 2012, the Company established a ten year Employee Stock Purchase Plan (“ESPP” or “the Plan”) for certain eligible employees. The Plan is to be administered by the Company’s Board of Directors. The total number of shares available for purchase under the Plan is 500 shares of the Company’s Common Stock. Employees participate over a six month period through payroll withholdings and may purchase, at the end of the six month period, the Company’s Common Stock at the lower of 85% of the fair market value on the first day of the offering period or the fair market value on the purchase date. No participant will be granted a right to purchase Common Stock under the Plan if such participant would own more than 5% of the total combined voting power of the Company. In addition, no participant may purchase more than a thousand shares of Common Stock within any purchase period.

The expected life of ESPP shares is the average of the remaining purchase period under each offering period. The assumptions used to value employee stock purchase rights during the three months ended March 31, 2013 and 2012 were as follows:

	Three Months Ended March 31,
	2013		2012
Expected stock price volatility	67	%	68	%
Risk-free interest rate	0.14	%	0.13	%
Expected life of options (in years)	0.50		0.50
Expected dividend yield	0	%	0	%

During the three months ended March 31, 2013 and 2012, the Company recorded $178 and $91, respectively, of compensation expense related to the ESPP. During the three months ended March 31, 2013, the Company sold a total of 35 shares of its Treasury Stock pursuant to purchases under its ESPP Plan. Cash received from purchases through the ESPP Plan during the three months ended March 31, 2013, was approximately $670 and is included within the financing activities section of the consolidated statements of cash flows. There were no shares purchased during the three months ended March 31, 2012. The total unrecognized compensation expense related to the ESPP as of March 31, 2013 was approximately $219, which is expected to be recognized over the remainder of the offering period.