Stock Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2016

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

The following table summarizes stock option activity:



	Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding as of January 1, 2016	3,716,520		$	7.76
Granted	30,185		$	8.97
Exercised	(8,098	)	$	3.92
Forfeited or expired	(4,896	)	$	16.74
Outstanding as of March 31, 2016	3,733,711		$	7.76	7.45	$	8,998,083
Options vested and expected to vest as of March 31, 2016	3,644,575		$	7.73	7.41	$	8,761,671
Options exercisable as of March 31, 2016	2,771,815		$	7.64	6.78	$	5,812,571

Ranges of Underlying Assumptions Used in BSM Option Pricing Model to Determine Fair Value of Stock Options Granted to Employees and Nonemployees

The following are the ranges of underlying assumptions used in the BSM option pricing model to determine the fair value of stock options granted to employee and to non-employees:



	Three Months Ended March 31,
	2016	2015
Employees:
Risk-free interest rate	1.7%	1.8% - 1.9%
Expected dividend yield	0%	0%
Expected volatility	77.1%	92.2%
Expected term of options (years)	6.0	5.9
Fair value of common stock	$8.97	$19.75 - $26.13
Non-employees:
Risk-free interest rate	0.6% - 1.4%	0.2% - 0.4%
Expected dividend yield	0%	0%
Expected volatility	76.9% - 84.9%	60.8% - 70.6%
Expected term of options (years)	0.8 - 5.5	0.3 - 1.8
Fair value of common stock	$9.07	$25.01

Schedule of Stock-based Compensation Expense for Stock Awards Recognized

Total stock-based compensation expense for all stock awards recognized in our condensed consolidated statements of operations is as follows (in thousands):



	Three Months Ended March 31,
	2016		2015
Employees:
Research and development	$	392	$	251
General and administrative	531		327
Total	$	923	$	578
Non-employees:
Research and development	$	63	$	217
General and administrative	12		8
Total	$	75	$	225