Preferred Stock	12 Months Ended
Dec. 31, 2018
Equity [Abstract]
Preferred Stock	Preferred Stock Series A Preferred Stock At various closing dates during the years ended December 31, 2015, 2014 and 2013, the Company issued 47,000,000 shares of Series A convertible preferred stock (“Series A Preferred Stock”) for $1.00 per share. The shares were issued in exchange for cash proceeds of $44.6 million, net of issuance costs of $0.1 million, and the exchange of approximately $2.3 million in outstanding convertible promissory notes, including accrued interest. Series B Preferred Stock During the year ended December 31, 2015, the Company issued 24,778,761 shares of Series B convertible preferred stock (“Series B Preferred Stock”) for $2.26 per share. This issuance resulted in cash proceeds of $55.8 million, net of issuance costs of $0.2 million. Series B-1 Preferred Stock During the year ended December 31, 2016, the Company issued 10,448,100 shares of Series B-1 Preferred Stock to Celgene for $3.46 per share. This issuance resulted in cash proceeds of $36.1 million, net of issuance costs of $0.1 million. Conversion of Preferred Stock Upon IPO Prior to the Company’s IPO, the holders of the Company’s Series A Preferred Stock, Series B Preferred Stock and Series B-1 Preferred Stock had certain voting rights, dividend rights, liquidation preferences and conversion privileges. Upon completion of the Company’s IPO, all shares of outstanding convertible preferred stock were automatically converted into an aggregate of 22,283,690 shares of common stock. All rights, preferences and privileges associated with the outstanding convertible preferred stock were terminated upon this conversion. The Company is now authorized to issue 5,000,000 shares of undesignated preferred stock in one or more series. As of December 31, 2018, no shares of preferred stock were issued or outstanding.

Preferred Stock

Series A Preferred Stock

At various closing dates during the years ended December 31, 2015, 2014 and 2013, the Company issued 47,000,000 shares of Series A convertible preferred stock (“Series A Preferred Stock”) for $1.00 per share. The shares were issued in exchange for cash proceeds of $44.6 million, net of issuance costs of $0.1 million, and the exchange of approximately $2.3 million in outstanding convertible promissory notes, including accrued interest.

Series B Preferred Stock

During the year ended December 31, 2015, the Company issued 24,778,761 shares of Series B convertible preferred stock (“Series B Preferred Stock”) for $2.26 per share. This issuance resulted in cash proceeds of $55.8 million, net of issuance costs of $0.2 million.

Series B-1 Preferred Stock

During the year ended December 31, 2016, the Company issued 10,448,100 shares of Series B-1 Preferred Stock to Celgene for $3.46 per share. This issuance resulted in cash proceeds of $36.1 million, net of issuance costs of $0.1 million.

Conversion of Preferred Stock Upon IPO

Prior to the Company’s IPO, the holders of the Company’s Series A Preferred Stock, Series B Preferred Stock and Series B-1 Preferred Stock had certain voting rights, dividend rights, liquidation preferences and conversion privileges. Upon completion of the Company’s IPO, all shares of outstanding convertible preferred stock were automatically converted into an aggregate of 22,283,690 shares of common stock. All rights, preferences and privileges associated with the outstanding convertible preferred stock were terminated upon this conversion.

The Company is now authorized to issue 5,000,000 shares of undesignated preferred stock in one or more series. As of December 31, 2018, no shares of preferred stock were issued or outstanding.