Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2015

The following table summarizes stock option activity for the six months ended June 30, 2015:


	Number of Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value ⁽¹⁾
Outstanding at December 31, 2014		5,067,957		$	33.52
Granted		581,083		$	115.77
Exercised		(519,560	)	$	22.77
Forfeited		(52,345	)	$	84.17

Outstanding at June 30, 2015		5,077,135		$	43.51		6.33	$	361.6

Vested and exercisable at June 30, 2015		3,399,023		$	24.62		5.18	$	304.5

⁽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 $114.20 of the Company’s common stock on June 30, 2015. The calculation excludes any awards with an exercise price higher than the closing price of the Company’s common stock on June 30, 2015. The amounts are presented in millions.

Summary of Restricted Stock Units

The following table summarizes restricted stock unit activity for the six months ended June 30, 2015:


	Number of Shares			Weighted- Average Grant-Date Fair Value
Unvested at December 31, 2014		483,580		$	76.20
Granted		230,812		$	112.91
Vested		(118,662	)	$	75.91
Forfeited		(23,039	)	$	89.76

Unvested at June 30, 2015		572,691		$	90.51

Summary of Stock Appreciation Rights Activity

The following table summarizes stock appreciation rights activity for the six months ended June 30, 2015:


	Number of Rights			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value ⁽¹⁾
Outstanding at December 31, 2014		688,228		$	24.05
Granted		—			—
Exercised		(26,912	)	$	23.20
Forfeited		(5,514	)	$	23.20

Outstanding at June 30, 2015		655,802		$	24.09		6.46	$	59.1

Vested and exercisable at June 30, 2015		564,384		$	24.11		6.46	$	50.8

(1)

Schedule of Black-Scholes Assumptions Used for Stock Options

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


	Three Months Ended June 30,		Six Months Ended June 30,
	2015	2014	2015	2014
Risk-free interest rate	1.33-1.78%	1.65-1.77%	1.33-1.78%	1.57-1.77%
Estimated term (in years)	4.99-5.50	5.09-5.50	4.98-5.50	5.09-5.50
Estimated volatility	50-57%	60-61%	50-57%	60-64%
Estimated dividend yield	—	—	—	—

Schedule of Black-Scholes Assumptions Used to Estimate Fair Value of Shares Issued under ESPP

The Black-Scholes assumptions used to estimate the fair value of shares issued under the ESPP on the commencement date of the offering period were as follows:


	Three Months Ended June 30,						Six Months Ended June 30,
	2015			2014			2015			2014
Risk-free interest rate		0.12	%		0.06	%		0.12	%		0.06	%
Estimated term (in years)		0.50			0.50			0.50			0.50
Estimated volatility		37	%		53	%		37	%		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,
	2015		2014		2015		2014
Stock-based compensation expense recognized as:
R&D expense	$	6,109	$	4,503	$	11,920	$	8,625
SG&A expense		7,969		6,678		15,530		12,217

Total	$	14,078	$	11,181	$	27,450	$	20,842