Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2014

The following table summarizes stock option activity for the three months ended March 31, 2014:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value ⁽¹⁾
Outstanding at December 31, 2013		6,614,534		$	22.12
Granted		644,185		$	76.84
Exercised		(657,452	)	$	9.76
Forfeited		(98,021	)	$	54.39

Outstanding at March 31, 2014		6,503,246		$	28.30		6.91	$	242.2

Vested and exercisable at March 31, 2014		3,985,481		$	16.33		5.79	$	191.5

⁽¹⁾

The aggregate intrinsic value is calculated as the pre-tax difference between the weighted average exercise price of the underlying awards and the closing price per share of $64.37 of the Company’s common stock on March 31, 2014. The calculation excludes any awards with an exercise price higher than the closing price of the Company’s common stock on March 31, 2014. The amounts are presented in millions.

Summary of Restricted Stock Units

Restricted Stock Units

The following table summarizes restricted stock unit activity for the three months ended March 31, 2014:


	Number of Shares			Weighted- Average Grant-Date Fair Value
Unvested at December 31, 2013		311,347		$	52.57
Granted		242,146		$	83.40
Vested		(2,500	)	$	54.36
Forfeited		(18,655	)	$	56.97

Unvested at March 31, 2014		532,338		$	66.63

Summary of Stock Appreciation Rights Activity

The following table summarizes stock appreciation rights activity for the three months ended March 31, 2014:


	Number of Rights		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value ⁽¹⁾
Outstanding at December 31, 2013		806,116	$	23.98
Granted		—	$	—
Exercised		—	$	—
Forfeited		—	$	—

Outstanding at March 31, 2014		806,116	$	23.98		7.81	$	32.6

Vested and exercisable at March 31, 2014		448,714	$	23.99		7.85	$	18.1

(1)

Schedule of Black-Scholes Assumptions Used for Stock Options and Stock Appreciation Rights

The Black-Scholes assumptions used to estimate the fair value of stock options granted during the period were as follows:


	Three Months Ended March 31,
	2014		2013
Risk-free interest rate		1.57%-1.65%		0.93-0.94%
Estimated term (in years)		5.23		5.24
Estimated volatility		64%		68%
Estimated dividend yield		—		—

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense was as follows:


	Three Months Ended March 31,
	2014		2013
Stock-based compensation expense recognized as:
R&D expense	$	4,122	$	3,818
SG&A expense		5,539		4,478

Total	$	9,661	$	8,296