Stockholders' Equity	3 Months Ended
Mar. 31, 2020
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Public Offerings In September 2019, the Company raised net proceeds of approximately $271.5 million from the sale of 7,187,500 shares of its common stock in a follow-on public offering, including 937,500 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares. In November 2018, the Company raised net proceeds of approximately $298.5 million from the sale of 18,602,941 shares of its common stock in a follow-on public offering, including 2,426,470 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares. In August 2016, the Company raised net proceeds of approximately $215.9 million from the sale of 6,969,696 shares of its common stock in a follow-on public offering, including 909,090 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares. In January 2016, the Company raised net proceeds of approximately $281.6 million from the sale of 10,344,827 shares of its common stock in a follow-on public offering. In connection with the January 2016 offering, the Company entered into a registration rights agreement (the “Registration Rights Agreement”) with 667, L.P., Baker Brothers Life Sciences, L.P. and 14159, L.P. (the “Baker Entities”), all of which are existing stockholders of the Company and are affiliated with two of its directors, Julian C. Baker and Dr. Stephen R. Biggar. Under the Registration Rights Agreement, the Company agreed that, if the Baker Entities demand that the Company register their shares of its common stock for resale under the Securities Act of 1933, as amended (the “Securities Act”), the Company would be obligated to effect such registration. The Company’s registration obligations under the Registration Rights Agreement cover all shares of its common stock now held or later acquired by the Baker Entities (including approximately $75.0 million, $43.0 million, $200.0 million, and $62.5 million of shares that the Baker Entities purchased at the public offering price in the January 2016, August 2016, November 2018, and September 2019 offerings, respectively), will continue in effect for up to 10 years, and include the Company’s obligation to facilitate certain underwritten public offerings of its common stock by the Baker Entities in the future. The Company has agreed to bear all expenses incurred by it in effecting any registration pursuant to the Registration Rights Agreement as well as the legal expenses of the Baker Entities of up to $50,000 per underwritten public offering effected pursuant to the Registration Rights Agreement. On May 3, 2019, pursuant to the Registration Rights Agreement, the Company filed a registration statement covering all shares owned by the Baker Entities as of April 29, 2019. Private Equity Financings In December 2012, the Company raised net proceeds of $80.5 million through the sale of 19,000,000 shares of its common stock at a price of $4.43 per share and the sale of warrants to purchase 500,000 shares of its common stock at a price of $4.42 per warrant share in a private equity financing. The warrants have an exercise price of $0.01 per share. In accordance with authoritative accounting guidance, the warrants’ value of $2.2 million was determined on the date of grant using the Black-Scholes model and recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the warrants to purchase 500,000 shares of common stock, of which 493,145 remained outstanding at March 31, 2020, may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent following such exercise.

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

8. Stockholders’ Equity

Public Offerings

In September 2019, the Company raised net proceeds of approximately $271.5 million from the sale of 7,187,500 shares of its common stock in a follow-on public offering, including 937,500 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares.

In November 2018, the Company raised net proceeds of approximately $298.5 million from the sale of 18,602,941 shares of its common stock in a follow-on public offering, including 2,426,470 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares.

In August 2016, the Company raised net proceeds of approximately $215.9 million from the sale of 6,969,696 shares of its common stock in a follow-on public offering, including 909,090 shares sold pursuant to the exercise in full of the underwriters’ option to purchase additional shares.

In January 2016, the Company raised net proceeds of approximately $281.6 million from the sale of 10,344,827 shares of its common stock in a follow-on public offering. In connection with the January 2016 offering, the Company entered into a registration rights agreement (the “Registration Rights Agreement”) with 667, L.P., Baker Brothers Life Sciences, L.P. and 14159, L.P. (the “Baker Entities”), all of which are existing stockholders of the Company and are affiliated with two of its directors, Julian C. Baker and Dr. Stephen R. Biggar. Under the Registration Rights Agreement, the Company agreed that, if the Baker Entities demand that the Company register their shares of its common stock for resale under the Securities Act of 1933, as amended (the “Securities Act”), the Company would be obligated to effect such registration. The Company’s registration obligations under the Registration Rights Agreement cover all shares of its common stock now held or later acquired by the Baker Entities (including approximately $75.0 million, $43.0 million, $200.0 million, and $62.5 million of shares that the Baker Entities purchased at the public offering price in the January 2016, August 2016, November 2018, and September 2019 offerings, respectively), will continue in effect for up to 10 years, and include the Company’s obligation to facilitate certain underwritten public offerings of its common stock by the Baker Entities in the future. The Company has agreed to bear all expenses incurred by it in effecting any registration pursuant to the Registration Rights Agreement as well as the legal expenses of the Baker Entities of up to $50,000 per underwritten public offering effected pursuant to the Registration Rights Agreement. On May 3, 2019, pursuant to the Registration Rights Agreement, the Company filed a registration statement covering all shares owned by the Baker Entities as of April 29, 2019.

Private Equity Financings

In December 2012, the Company raised net proceeds of $80.5 million through the sale of 19,000,000 shares of its common stock at a price of $4.43 per share and the sale of warrants to purchase 500,000 shares of its common stock at a price of $4.42 per warrant share in a private equity financing. The warrants have an exercise price of $0.01 per share. In accordance with authoritative accounting guidance, the warrants’ value of $2.2 million was determined on the date of grant using the Black-Scholes model and recorded as a component of stockholders’ equity within additional paid-in capital. Per their terms, the warrants to purchase 500,000 shares of common stock, of which 493,145 remained outstanding at March 31, 2020, may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent following such exercise.