Shared-Based Payments (Tables)

12 Months Ended

Dec. 31, 2013

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock-Based Compensation Expense

The following stock-based compensation amounts were recognized for the periods indicated:


	Year Ended December 31,
	2013		2012		2011
Research and development	$	507,142	$	471,809	$	1,018,935
General and administrative		355,020		366,586		1,328,504

Total stock-based compensation expense	$	862,162	$	838,395	$	2,347,439

Schedule of Fair Value Option Award Estimated on the Date of Grant Using the Black-Scholes Option-Pricing Model

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions in the following table:


	Year Ended December 31,
	2013	2012	2011
Expected dividend yield..	0%	0%	0%
Expected volatility	53% - 67%	51%	62%
Risk-free interest rate	1.24% - 2.19%	1.18%	1.35%
Expected term.	7 years	7 years	7 years
Expected forfeiture rate..	5.06% - 5.57%	5.57%	5.58%

Schedule of Stock Option Activity

The following table summarizes stock option activity for 2013:


	Shares			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2012		3,249,541		$	0.94		7.3
Granted		1,307,101			10.70
Exercised		(1,268,049	)		0.85
Forfeited or expired		(87,635	)		1.11

Outstanding, December 31, 2013		3,200,958			4.90		6.9	$	67,532

December 31, 2013:
Exercisable		1,688,251			0.94		4.8		42,311
Vested and expected to vest		3,022,948			4.64		6.8		64,574