Net Loss Per Share Attributable to Common Stockholders

3 Months Ended

Mar. 31, 2014

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

2. NET LOSS PER SHARE ATTRIBUTABLE TO COMMON STOCKHOLDERS

The Company calculates basic and diluted net loss per common share by dividing the net loss by the weighted average number of common shares outstanding during the period. The Company has excluded all potentially dilutive shares, which include outstanding common stock options, unvested restricted stock, and shares under the Company’s Employee Stock Purchase Plan (“ESPP”), from the weighted average number of common shares outstanding as their inclusion in the computation for all periods would be anti-dilutive due to net losses. The Company’s unvested restricted stock awards are not considered participating securities under the authoritative guidance since any dividends earned on unvested restricted shares are required to be returned if unvested shares are forfeited.

The following common stock equivalents were excluded from the computation of diluted net loss per share attributable to common stockholders because they had an anti-dilutive impact (in thousands):

	Three Months Ended March 31,
	2014		2013
Options to purchase common stock		2,957		4,147
Unvested restricted stock		1,044		778
Employee Stock Purchase Program		12		—