Shareholders’ Equity

2017 Common Stock Offering

In March 2017, the Company offered and sold 3,731,344 shares of common stock in an underwritten public offering at a price of $33.50 per share for gross proceeds of approximately $125.0 million. The Company received proceeds of approximately $117.5 million, net of approximately $7.5 million in underwriting commissions, discounts and other issuance costs.

2018 Common Stock Offering

In March 2018, the Company offered and sold 3,910,000 shares of common stock in an underwritten public offering at a price of $29.50 per share for gross proceeds of approximately $115.3 million. The Company received proceeds of approximately $109.8 million, net of approximately $5.5 million in underwriting commissions, discounts and other issuance costs.

Stock Option Activity

The Company’s stock option activity under its option plans for the six months ended June 30, 2018 was comprised of the following:



	Shares Underlying Stock Options		Weighted- average Exercise Price per Share
Outstanding at December 31, 2017	6,037,302		$	24.19
Granted	886,900		$	30.15
Exercised	(97,937	)	$	17.54
Forfeited	(140,757	)	$	26.35
Outstanding at June 30, 2018	6,685,508		$	25.03

As of June 30, 2018, there were 1,129,589 shares of common stock available for future grants under its option plans, and the Company has reserved an additional 6,685,508 shares of common stock for future issuance upon exercise of all outstanding stock options granted under its option plans.

During the six months ended June 30, 2018, stock options to purchase 97,937 shares of common stock were exercised with an intrinsic value of $1.4 million.

Share-based Compensation Expense

Total share-based compensation expense related to all share-based awards for the three and six months ended June 30, 2018 and 2017 was comprised of the following (in thousands):



	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development:
Stock options	$	5,695	$	2,563	$	11,081	$	5,016
Warrants	6		16		16		33
Research and development share-based compensation expense	5,701		2,579		11,097		5,049
Selling, general and administrative:
Stock options	4,143		1,993		8,149		3,948
Restricted stock	—		—		—		409
Warrants	—		139		—		288
Selling, general and administrative share-based compensation expense	4,143		2,132		8,149		4,645
Total share-based compensation expense	$	9,844	$	4,711	$	19,246	$	9,694

As of June 30, 2018, $98.0 million of total unrecognized share-based compensation expense related to unvested stock options remains and is expected to be recognized over a weighted-average period of 3.1 years.

Warrants

As of June 30, 2018, the Company had outstanding warrants to purchase 10,000 shares of common stock. In March 2018, the Company issued 43,056 shares of common stock in a cashless exercise of 83,013 warrants to a third-party warrant holder.