4. Share Based Compensation

The Company has Stock Incentive Plans (the Plans) pursuant to which the Company’s board of directors may grant stock options or restricted stock to employees. The Company is authorized to issue grants of restricted stock and stock options to purchase up to 26,963,150 shares as of March 31, 2014 and December 31, 2013. There were 6,871,047 additional shares remaining available for grant under the Plans at March 31, 2014.

The table below summarizes the expense recognized related to share-based payments recognized for the three month periods ended March 31 (in thousands):


	Three Months Ended March 31,
	2014		2013
Stock options	$	3,412	$	2,871
Restricted stock		7,200		1,291

Stock-based compensation	$	10,612	$	4,162

The tax benefits recorded on stock based compensation were $3.6 million and $1.3 million for the three month periods ended March 31, 2014 and 2013, respectively.

The following table summarizes the Company’s total unrecognized compensation cost related to stock-based compensation as of March 31, 2014 (in thousands):


	Unrecognized Compensation Cost		Weighted Average Period of Expense Recognition (in Years)
Stock options	$	24,909		1.54
Restricted stock		18,172		1.02

Total	$	43,081

Stock Options

Stock options are granted with an exercise price estimated to be equal to the fair market value on the date of grant as authorized by the Company’s board of directors. Options granted have vesting provisions ranging from one to six years. Certain stock option awards also have performance vesting provisions. Stock option grants are generally subject to forfeiture if employment terminates prior to vesting.

The following summarizes the changes in the number of shares of common stock under option for the three month period ended March 31, 2014 (shares and aggregate intrinsic value in thousands):


	Shares			Weighted Average Exercise Price		Options Exercisable at End of Period		Weighted Average Exercise Price of Exercisable Options		Weighted Average Fair Value of Options Granted During the Period		Aggregate Intrinsic Value
Outstanding at December 31, 2013		5,331		$	25.68		2,589	$	16.57			$	487,673
Granted		197			106.83					$	30.93
Exercised		(359	)		12.63								36,803
Forfeited		(19	)		47.63

Outstanding at March 31, 2014		5,150		$	29.61		2,270	$	17.63			$	440,198

Expected to vest as of March 31, 2014		5,150		$	29.61

The aggregate intrinsic value of stock options exercisable at March 31, 2014 was $221.3 million. The weighted average contractual term of options exercisable at March 31, 2014 was 5.9 years.

The fair value of stock option awards granted was estimated using the Black-Scholes option pricing model during the three months ended March 31, 2014 and 2013, with the following weighted-average assumptions for grants during the period.


	March 31
	2014			2013
Risk-free interest rate		0.95	%		0.57	%
Dividend yield		—			—
Expected volatility		34.91	%		34.84	%
Expected life (in years)		4.0			4.0

Restricted Stock

Awards of restricted stock and restricted stock units are independent of stock option grants and are generally subject to forfeiture if employment terminates prior to vesting. The vesting of the restricted stock and restricted stock units granted is generally based on the passage of time, performance or market conditions. Shares vesting based on the passage of time have vesting provisions ranging from one to four years.

The fair value of restricted stock granted based on market conditions was estimated using the Monte Carlo option pricing model at the grant date. The risk-free interest rate and volatility assumptions for restricted stock shares granted with market conditions were calculated consistently with those applied in the Black-Scholes options pricing model utilized in determining the fair value of the stock option awards. No such awards were granted during the three months ended March 31, 2014 and 2013.

The following table summarizes the changes in the number of shares of restricted stock and restricted stock units for the three months ended March 31, 2014 (shares in thousands):


	Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2013		634		$	67.83
Granted		38			106.83
Vested		(115	)		93.88

Unvested at March 31, 2014		557		$	65.12