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 three months ended March 31, 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	701,900		$	30.02
Exercised	(33,854	)	$	15.62
Forfeited	(84,178	)	$	24.77
Outstanding at March 31, 2018	6,621,170		$	24.84

As of March 31, 2018, there were 1,258,010 shares of common stock available for future grants under its option plans, and the Company has reserved an additional 6,621,170 shares of common stock for future issuance upon exercise of all outstanding stock options granted under its option plans.

During the three months ended March 31, 2018, stock options to purchase 33,854 shares of common stock were exercised with an intrinsic value of $0.5 million.

Share-based Compensation Expense

Total share-based compensation expense related to all share-based awards for the three months ended March 31, 2018 and 2017 was comprised of the following (in thousands):



	Three Months Ended March 31,
	2018		2017
Research and development:
Stock options	$	5,386	$	2,453
Warrants	10		17
Research and development share-based compensation expense	5,396		2,470
Selling, general and administrative:
Stock options	4,006		1,955
Restricted stock	—		409
Warrants	—		149
Selling, general and administrative share-based compensation expense	4,006		2,513
Total share-based compensation expense	$	9,402	$	4,983

As of March 31, 2018, $103.7 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 3.2 years.

Warrants

As of March 31, 2018, the Company had outstanding warrants to purchase 10,000 shares of common stock. During the three months ended March 31, 2018, the Company issued 43,056 shares of common stock in a cashless exercise of 83,013 warrants to a third-party warrant holder.