Stock Based Compensation

3 Months Ended

Mar. 31, 2014

Stock Based Compensation

8. Stock Based Compensation

In January 2013, our Board of Directors adopted our 2013 Equity Incentive Plan, or the 2013 Plan, which became effective upon of the closing of our IPO in May 2013. On January 1, 2014, the number of shares available for issuance under the 2013 Plan automatically increased by a number of shares equal to 5% of the total common stock outstanding at December 31, 2013. As of March 31, 2014 there were 6,949,108 shares reserved under the 2013 Plan for the issuance of awards.

The following table summarizes option activity under our 2013 Equity Incentive Plan and related information during the three months ended March 31, 2014:

				Shares
				Subject to			Weighted-
	Shares Available			Outstanding			Average Exercise
	for Grant			Options			Price Per Share
Balance at December 31, 2013		81,948			3,708,773		$	9.43
Options authorized		2,045,785			—			—
Options granted		(671,613	)		671,613			25.14
Options exercised		—			(157,833	)		6.39
Options canceled		19,732			(19,732	)		17.76
Balance at March 31, 2014		1,475,852			4,202,821		$	12.02

The estimated grant date fair values of the employee stock options were calculated using the Black Scholes valuation model, based on the following assumptions:

	Three Months Ended March 31,
	2014			2013
Risk-free interest rate		1.88	%		1.10	%
Expected life	6.0 years			6.0 years
Expected Volatility		79	%		72	%
Dividend yield		—			—