Convertible Preferred Stock	12 Months Ended
Dec. 31, 2013
Equity [Abstract]
Convertible Preferred Stock	7. Convertible Preferred Stock In 2008 and 2009, the Company sold a total of 33,188,889 shares of Series A convertible preferred stock to investors at $1.00 per share, resulting in aggregate proceeds of $33.1 million, including the conversion of the principal and interest on $2.0 million of convertible notes. In April 2010, the Company executed a strategic collaboration agreement with Celgene Corporation (Note 3). In connection with the Celgene Agreement, the Company sold 5,190,551 shares of Series B convertible preferred stock (Series B Preferred Stock) to Celgene at $1.70 per share, resulting in aggregate proceeds of $8.8 million. The Company determined the fair value per share of the Series B Preferred Stock on the date of issuance to be $1.11 and has considered the premium paid over the fair value of the Series B Preferred Stock to be additional consideration under the Celgene Agreement. Refer to Note 3 for further discussion of the treatment of the implied premium on the Series B Preferred Stock. In November 2011, the Company completed a Series C convertible preferred stock financing, pursuant to which the Company sold 15,882,389 shares of Series C convertible preferred stock to investors at $4.91 per share, resulting in aggregate proceeds of $78.0 million. The shares of Series C convertible preferred stock included 7,395,829 shares of Series C-1 convertible preferred stock (the C-1 Preferred Stock) and 8,486,560 shares of Series C-2 convertible preferred stock (the C-2 Preferred Stock) (collectively, the Series C Preferred Stock). The Company assessed the Series A, B and C Preferred Stock (collectively, the “Preferred Stock”) for any embedded derivatives that would require bifurcation from the Preferred Stock and receive separate accounting treatment. No embedded derivatives were identified that would require bifurcation. In connection with the closing of the IPO, all of the Company’s outstanding convertible preferred stock automatically converted to common stock, resulting in an additional 19,731,564 shares of common stock of the Company becoming outstanding. Further, under the terms of the certificate of incorporation, the Board of Directors is authorized to direct the Company to issue shares of preferred stock in one or more series without stockholder approval. The Board of Directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock. As of December 31, 2013, there are no shares of preferred stock outstanding. Prior to the IPO, the holders of the Preferred Stock Series A, Series B, and Series C Preferred Stock were entitled to receive cumulative dividends at the rate of $0.06, $0.10, and $0.294666 per share per annum, respectively, in preference to any dividends on common stock, when, as, and if declared by the Board of Directors. These dividends were cumulative and accrued whether or not declared. As of December 31, 2012, dividends accrued but unpaid were $7.8 million for Series A Preferred Stock, $1.4 million for Series B Preferred Stock, and $5.3 million for Series C Preferred Stock. Immediately prior to the IPO, dividends accrued but unpaid were $8.9 million for Series A Preferred Stock, $1.7 million for Series B Preferred Stock, and $8.0 million for Series C Preferred Stock.

7. Convertible Preferred Stock

In 2008 and 2009, the Company sold a total of 33,188,889 shares of Series A convertible preferred stock to investors at $1.00 per share, resulting in aggregate proceeds of $33.1 million, including the conversion of the principal and interest on $2.0 million of convertible notes.

In April 2010, the Company executed a strategic collaboration agreement with Celgene Corporation (Note 3). In connection with the Celgene Agreement, the Company sold 5,190,551 shares of Series B convertible preferred stock (Series B Preferred Stock) to Celgene at $1.70 per share, resulting in aggregate proceeds of $8.8 million. The Company determined the fair value per share of the Series B Preferred Stock on the date of issuance to be $1.11 and has considered the premium paid over the fair value of the Series B Preferred Stock to be additional consideration under the Celgene Agreement. Refer to Note 3 for further discussion of the treatment of the implied premium on the Series B Preferred Stock.

In November 2011, the Company completed a Series C convertible preferred stock financing, pursuant to which the Company sold 15,882,389 shares of Series C convertible preferred stock to investors at $4.91 per share, resulting in aggregate proceeds of $78.0 million. The shares of Series C convertible preferred stock included 7,395,829 shares of Series C-1 convertible preferred stock (the C-1 Preferred Stock) and 8,486,560 shares of Series C-2 convertible preferred stock (the C-2 Preferred Stock) (collectively, the Series C Preferred Stock).

The Company assessed the Series A, B and C Preferred Stock (collectively, the “Preferred Stock”) for any embedded derivatives that would require bifurcation from the Preferred Stock and receive separate accounting treatment. No embedded derivatives were identified that would require bifurcation.

In connection with the closing of the IPO, all of the Company’s outstanding convertible preferred stock automatically converted to common stock, resulting in an additional 19,731,564 shares of common stock of the Company becoming outstanding. Further, under the terms of the certificate of incorporation, the Board of Directors is authorized to direct the Company to issue shares of preferred stock in one or more series without stockholder approval. The Board of Directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock. As of December 31, 2013, there are no shares of preferred stock outstanding.

Prior to the IPO, the holders of the Preferred Stock Series A, Series B, and Series C Preferred Stock were entitled to receive cumulative dividends at the rate of $0.06, $0.10, and $0.294666 per share per annum, respectively, in preference to any dividends on common stock, when, as, and if declared by the Board of Directors. These dividends were cumulative and accrued whether or not declared. As of December 31, 2012, dividends accrued but unpaid were $7.8 million for Series A Preferred Stock, $1.4 million for Series B Preferred Stock, and $5.3 million for Series C Preferred Stock. Immediately prior to the IPO, dividends accrued but unpaid were $8.9 million for Series A Preferred Stock, $1.7 million for Series B Preferred Stock, and $8.0 million for Series C Preferred Stock.