Share-Based Payments (Tables)

6 Months Ended

Jun. 30, 2013

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

During the six months ended June 30, 2013, the Company granted 3,636 stock options to consultants of the Company. These awards are included within the following table which summarizes the activity of the Plan for the six months ended June 30, 2013:


	Number of Stock Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)

Outstanding at December 31, 2012		3,145,544		$	0.88		7.72	$	15,402
Granted		613,600			9.05
Exercised		(57,985	)		0.70
Forfeited		(44,014	)		2.08

Outstanding at June 30, 2013		3,657,145			2.24		7.65		24,897

Exercisable at June 30, 2013		2,130,507			0.57		6.75		18,084

Vested and expected to vest at June 30, 2013		2,887,672			1.33		7.23		22,299

Unvested Restricted Stock Activity

Unvested restricted stock activity for the six months ended June 30, 2013 is summarized as follows:


	Six Months Ended June 30, 2013
Unvested shares beginning of period		160,053
Vested		(96,213	)

Unvested shares end of period		63,840

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

During the three and six months ended June 30, 2013 and 2012, the Company recorded stock-based compensation expense for employee and non-employee stock options and restricted stock, which was allocated as follows in the consolidated statements of operations (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2013		2012		2013		2012
Research and development expense	$	246	$	60	$	533	$	126
General and administrative expense		83		31		220		63

	$	329	$	91	$	753	$	189

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,
	2013			2012			2013			2012
Risk-free interest rate		1.00	%		1.18	%		1.00	%		1.13	%
Expected dividend yield		—			—			—			—
Expected term (in years)		6.49			6.42			6.49			6.12
Expected volatility		91.85	%		104.80	%		91.85	%		99.05	%