Share-Based Payments (Tables)

6 Months Ended

Jun. 30, 2014

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Award Activity

The following table summarizes the activity of all stock incentive plans for the six months ended June 30, 2014:

	Number of Stock Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2013		3,846,168		$	4.14		7.43	$	76,189
Granted		1,072,809			32.76
Exercised		(912,783	)		1.14
Forfeited/cancelled		(22,633	)		4.45
Outstanding at June 30, 2014		3,983,561		$	12.54		7.85	$	132,591
Exercisable at June 30, 2014		1,720,163		$	1.43		6.19	$	76,357
Vested and expected to vest at June 30, 2014		3,297,987		$	11.77		7.62	$	112,303

Unvested Restricted Stock Activity

Unvested restricted stock activity for the six months ended June 30, 2014 is summarized as follows:

	Six Months Ended June 30, 2014
Unvested shares beginning of period		23,295
Vested		(9,091	)
Unvested shares end of period		14,204

Recorded Stock-Based Compensation Expense for Employee and Non-Employee Stock Options and Restricted Stock

During the three and six months ended June 30, 2014 and 2013, the Company recorded stock-based compensation expense for employee and non-employee stock options and restricted stock, which was allocated as follows in the condensed consolidated interim statements of operations (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2014		2013		2014		2013
Research and development expense	$	1,397	$	246	$	2,461	$	533
General and administrative expense		984		83		1,425		220
	$	2,381	$	329	$	3,886	$	753

Schedule of Fair Value Option Award Weighted Average Assumptions Used

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

	Three Months Ended June 30,						Six Months Ended June 30,
	2014			2013			2014			2013
Risk-free interest rate		1.81	%		1.00	%		1.82	%		1.00	%
Expected dividend yield		—			—			—			—
Expected term (in years)		5.89			6.49			6.02			6.49
Expected volatility		88.00	%		91.85	%		85.34	%		91.85	%