Subsequent Events

12 Months Ended

Dec. 31, 2017

Subsequent Events [Abstract]

Subsequent Events

10. Subsequent events

In January 2018, we completed an underwritten public offering of 7,675,072 shares of common stock, including 675,072 from the exercise by the underwriters of their option to purchase additional shares, at an offering price of $18.25 per share.  We received net proceeds of approximately $131.4 million, after deducting underwriting discounts and commissions and offering expenses.