Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2015

Recognized Expense of Share Based Compensation

Employee stock-based compensation for the three and nine months ended September 30, 2015 and 2014, were as follows (in thousands, except share and per share data):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Stock-based compensation:
Options -
Research and development, or R&D	$	19,867	$	8,726	$	60,594	$	17,690
General and administrative, or G&A		4,747		1,377		12,173		4,081
Performance shares - R&D		342		346		487		1,008
Total stock-based compensation expense	$	24,956	$	10,449	$	73,254	$	22,779
Impact on basic and diluted net loss per share	$	0.77	$	0.35	$	2.29	$	0.76
Weighted average shares (basic and diluted)		32,303,203		30,117,819		32,018,869		29,936,254

Stock Options

			Weighted
			Average
			Grant-Date
Performance shares	Shares		Fair Value
Nonvested shares at December 31, 2014		18,942	$	102.46
Granted		—		—
Vested/Issued		—		—
Cancelled		—		—
Nonvested shares at September 30, 2015		18,942	$	102.46

				Weighted
				Average
				Grant-Date
Stock options	Shares			Fair Value
Nonvested shares at December 31, 2014		2,591,565		$	81.33
Granted		1,402,786			89.17
Vested/Issued		(977,257	)		61.22
Forfeited		(214,110	)		110.20
Nonvested shares at September 30, 2015		2,802,984			90.95

Fair Value Options Weighted-Average Assumptions

The fair value of options granted to employees was estimated using the Black-Scholes Option Pricing Method (see Note 2—Significant Accounting Policies) with the following weighted-average assumptions used during the nine months ended September 30, 2015 and 2014:

	2015			2014
Dividend yield		0.0	%		0.0	%
Expected volatility		63.4	%		81.8	%
Risk-free interest rate		1.6	%		1.8	%
Expected life in years		5.85			5.85

Activity with Respect to Options Granted

Activity with respect to options granted under the 2011 Plan is summarized as follows:

	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2014		3,978,126		$	89.55		8.7	$	431,635
Granted		1,402,786		$	153.65		9.5		—
Forfeited		(214,110	)	$	188.10		—		—
Exercised		(720,253	)	$	36.20		—	$	93,368
Expired		(2,291	)	$	117.84
Outstanding at September 30, 2015		4,444,258		$	70.12		8.5	$	80,264
Nonvested at September 30, 2015		2,802,984		$	150.43		9.2	$	10,135
Exercisable at September 30, 2015		1,641,274		$	50.87		7.3	$	70,129