Stock-Based Compensation

3 Months Ended

Mar. 31, 2012

Stock-Based Compensation

Stock-Based Compensation

9.  Stock-Based Compensation

During the three months ended March 31, 2011 and 2012, the Company did not issue options to purchase shares of common stock.

As of December 31, 2011 and March 31, 2012, there were 830,000 and 866,111 shares of common stock, respectively, available to be issued under the 2008 Stock Incentive Plan, as amended (the “2008 Plan”).

The 2011 Stock Incentive Plan (the “2011 Plan”) became effective upon closing of the Company’s initial public offering in April 2012. Upon effectiveness of the 2011 Plan, no further awards were available to be issued under the 2008 Plan. The 2011 Plan is administered by the Board of Directors of the Company and permits the Company to grant incentive and non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. The 2011 Plan increases the total number of shares of common stock available to be issued by 3.5 million.

The Company recognized stock-based compensation expense as follows for the three months ended March 31, 2011 and 2012:

	Three months ended March 31,
(in thousands)	2011		2012
Employee awards:
Research and development	$	700	$	909
General and administrative	273		430
Stock-based compensation for employee awards	973		1,339
Stock-based compensation for nonemployee awards	47		—
Total stock-based compensation	$	1,020	$	1,339

The following table summarizes stock option activity during the three months ended March 31, 2012:

(in thousands, except per share amounts)	Number of shares		Weighted average exercise price		Aggregate intrinsic value
Outstanding, December 31, 2011	17,617		$	2.56	$	74,329
Exercised	(66	)	$	2.24
Forfeited	(36	)	$	3.37
Outstanding, March 31, 2012	17,515		$	2.56	$	63,769
Exercisable, March 31, 2012	14,171		$	2.23	$	56,177
Vested and expected to vest, March 31, 2012	17,339		$	2.54	$	63,485

The aggregate intrinsic value was calculated as the difference between the exercise price of the stock options and the fair value of the underlying common stock as of the respective balance sheet date.