Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Company's Stock Option Activity

The following table summarizes the stock option activity of all stock incentive plans for the year ended December 31, 2015.

	Number of Stock Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2014		3,805,420		$	17.19		7.58	$	360,935
Granted		1,461,240			104.14
Exercised		(560,317	)		10.44
Forfeited/Expired		(87,646	)		73.77
Outstanding at December 31, 2015		4,618,697		$	44.45		7.49	$	153,573
Exercisable at December 31, 2015		2,115,905		$	11.51		6.02	$	113,912
Vested and expected to vest at December 31, 2015		4,312,356		$	44.58		7.44	$	142,943

Unvested Stock Unit Activity

Unvested RSU activity for the year ended December 31, 2015 is summarized as follows:

	Number of Stock Units			Weighted-average grant date fair value
Unvested shares at December 31, 2014		10,000		$	50.24
Granted		15,000			122.22
Vested		(10,000	)		50.24
Unvested shares at December 31, 2015		15,000		$	122.22

Unvested Stock Unit Activity

Unvested restricted stock activity for the year ended December 31, 2015 is summarized as follows:

Unvested shares at December 31, 2014	8,522
Granted	—
Vested	(8,522	)
Forfeited	—
Unvested shares at December 31, 2015	—

Stock-Based Compensation Expense for Employee and Non-employee Stock Options, Performance-Based Stock Options, ESPP Shares, Performance-Based Stock Units, Restricted Stock Units and Restricted Stock

During the years ended December 31, 2015, 2014, and 2013, the Company recorded stock-based compensation expense for employee and non-employee stock options, performance-based stock options, ESPP shares, performance-based stock units, restricted stock units and restricted stock, which was allocated as follows in the consolidated statements of operations (in thousands):

	Years Ended December 31,
	2015		2014		2013
Research and development expense	$	17,419	$	6,688	$	2,001
General and administrative expense		14,544		4,818		1,029
	$	31,963	$	11,506	$	3,030

Schedule of Grant Date Fair Value Option Award Weighted Average Assumptions Used

The following table summarizes the weighted-average assumptions used in calculating the grant date fair value of the awards:

	Years Ending December 31,
	2015			2014			2013
Risk-free interest rate		1.71	%		1.83	%		1.31	%
Expected dividend yield		—			—			—
Expected term (in years)		6.04			6.03			6.42
Expected volatility		69.62	%		78.61	%		92.49	%