Stock Based Compensation

3 Months Ended

Mar. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

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 initial public offering in May 2013. On January 1, 2016, 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, 2015. As of March 31, 2016 there were 12,205,425 shares reserved under the 2013 Plan for the future issuance of equity awards.

Stock Options

The following table summarizes stock option activity under our 2013 Plan and related information:

	Shares
	Subject to			Weighted-
	Outstanding			Average Exercise
	Options			Price Per Share
Balance at December 31, 2015		4,731,483		$	24.19
Options granted		980,215		$	32.51
Options exercised		(10,984	)	$	15.52
Options canceled		(85,230	)	$	28.85
Balance at March 31, 2016		5,615,484		$	25.59

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

	For the Three Months Ended March 31,
	2016			2015
Risk-free interest rate		1.61	%		1.54	%
Expected life	6.0 years			6.0 years
Expected volatility		64	%		66	%
Dividend yield	—			—

Restricted stock units (“RSUs”)

In January 2015, the Compensation Committee of our Board of Directors approved the commencement of granting restricted stock units, to our employees. RSUs are share awards that entitle the holder to receive freely tradable shares of our Common Stock upon vesting.

The following table summarizes RSU activity, under our 2013 Plan and related information:

	Shares
	Subject to			Weighted-
	Outstanding			Average grant date
	RSUs			fair value per share
Balance at December 31, 2015		167,750		$	30.86
RSUs granted		215,655		$	33.49
RSUs released		(55,195	)	$	30.88
RSUs canceled		(9,982	)	$	31.67
Balance at March 31, 2016		318,228		$	32.62

Performance stock units (“PSUs”)

In January 2015, the Compensation Committee of our Board of Directors approved the commencement of granting performance stock units, to our employees. PSUs are share awards that entitle the holder to receive freely tradable shares of our Common Stock upon achievement of specified conditions. In January 2016, the Compensation Committee of our Board of Directors approved a program to award up to 102,906 PSUs to the management team based on the achievement of certain commercial and regulatory goals related to andexanet alfa and betrixaban, respectively. At March 31, 2016 the achievement of such performance conditions was not deemed probable and therefore no expense has been recognized pursuant to these awards for the three months ended March 31, 2016.

The following table summarizes PSU activity, under our 2013 Plan and related information:

	Shares
	Subject to			Weighted-
	Outstanding			Average grant date
	PSU's			fair value per share
Balance at December 31, 2015		205,261		$	29.33
PSUs granted		102,906			33.49
PSUs released		(13,170	)		50.00
PSUs canceled		(1,303	)		49.44
Balance at March 31, 2016		293,694			29.77

The table below sets forth the functional classification of stock-based compensation expense, net of estimated forfeitures, for the periods presented (in thousands):

	For the Three Months Ended March 31,
	2016		2015
Research and development	$	3,030	$	2,209
Selling, general and administrative		4,039		2,963
Total stock-based compensation	$	7,069	$	5,172