Warrants

3 Months Ended

Mar. 31, 2016

Equity [Abstract]

Warrants

Warrants 

As of March 31, 2016 the following warrants for common stock were issued and outstanding:

Issue date	Expiration date	Exercise price		Number of warrants outstanding
November 21, 2012	November 21, 2017	$	7.86	695,383

During the three months ended March 31, 2016, warrants for 419,244 shares of the Company's common stock were exercised via cashless exercises and 313,756 shares were exercised for cash generating proceeds of $2.1 million and the Company issued a total of 603,545 shares, of common stock. During the three months ended March 31, 2015, warrants for 13,274 shares of the Company's common stock were exercised via cashless exercises and the Company issued a total of 9,315 shares of common stock.

Stockholders' Equity

Share-based Compensation

Total share-based compensation expense by operating statement classification is presented below (in thousands):

	Three Months Ended March 31,
	2016		2015
Research and development expense	$	1,458	$	808
General and administrative expense	1,580		1,508
	$	3,038	$	2,316

During the three months ended March 31, 2016 and 2015, 20,296 and 22,166 shares were issued pursuant to stock option exercises generating net proceeds of $0.2 million and $0.3 million, respectively.