Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2014

The following table summarizes stock option activity for the six months ended June 30, 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		798,307		$	74.77
Exercised		(812,059	)	$	10.71
Forfeited		(179,472	)	$	51.62
Expired		(243	)	$	48.18

Outstanding at June 30, 2014		6,421,067		$	29.28		6.62	$	308.6

Vested and exercisable at June 30, 2014		4,164,218		$	17.71		5.55	$	247.2

⁽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 $77.08 of the Company’s common stock on June 30, 2014. The calculation excludes any awards with an exercise price higher than the closing price of the Company’s common stock on June 30, 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 six months ended June 30, 2014:


	Number of Shares			Weighted- Average Grant-Date Fair Value
Unvested at December 31, 2013		311,347		$	52.57
Granted		318,569		$	79.55
Vested		(37,952	)	$	53.11
Forfeited		(36,071	)	$	59.18

Unvested at June 30, 2014		555,893		$	67.57

Summary of Stock Appreciation Rights Activity

The following table summarizes stock appreciation rights activity for the six months ended June 30, 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 June 30, 2014		806,116	$	23.98		7.38	$	42.8

Vested and exercisable at June 30, 2014		500,767	$	23.98		7.32	$	26.6

⁽¹⁾

Schedule of Black-Scholes Assumptions Used for Stock Options

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


	Three Months Ended June 30,		Six Months Ended June 30,
	2014	2013	2014	2013
Risk-free interest rate	1.65-1.77%	0.73-1.55%	1.57-1.77%	0.73-1.55%
Estimated term (in years)	5.09-5.50	5.25-5.50	5.09-5.50	5.24-5.50
Estimated volatility	60-61%	73-75%	60-64%	68-75%
Estimated dividend yield	—	—	—	—

Schedule of Black-Scholes Assumptions Used in Estimating Fair Value of Shares Issued under ESPP

The fair value of shares issued under the ESPP was estimated on the commencement date of the offering period using the Black-Scholes model and the following assumptions:


	Three Months Ended June 30, 2014			Six Months Ended June 30, 2014
Risk-free interest rate		0.06	%		0.06	%
Estimated term (in years)		0.50			0.50
Estimated volatility		53	%		53	%
Estimated dividend yield		—			—

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense was as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
	2014		2013		2014		2013
Stock-based compensation expense recognized as:
R&D expense	$	4,503	$	3,619	$	8,625	$	7,437
SG&A expense		6,678		4,512		12,217		8,990

Total	$	11,181	$	8,131	$	20,842	$	16,427