Debt	6 Months Ended
Jun. 30, 2018
Debt Disclosure [Abstract]
Debt	DEBT In October 2015, we completed the sale of $125 million of the Old Notes, in a private placement, or the Private Placement, to funds managed by Baupost pursuant to a Notes Purchase Agreement dated October 14, 2015. The Old Notes were issued under an Indenture, or the Indenture, dated as of October 15, 2015, with The Bank of New York Mellon Trust Company, N.A. as trustee, or the Trustee. The Indenture subjected us to certain financial and business covenants and contained restrictions on the payments of cash dividends. The Indenture contained customary terms and events of default. If an event of default (other than certain events of bankruptcy, insolvency or reorganization involving us) occured and was continuing, the Trustee by notice to us, or the holders of at least 25% in aggregate principal amount of the outstanding Old Notes by written notice to us and the Trustee, could have declared 100% of the principal on all of the Old Notes to be due and payable. Upon such a declaration of acceleration, such principal would be due and payable immediately. Upon the occurrence of certain events of bankruptcy, insolvency or reorganization involving us, 100% of the principal on all of the Old Notes would have become due and payable automatically. Further, in connection with the Private Placement, we entered into a Registration Rights Agreement with the purchasers of the Old Notes, or the Registration Rights Agreement, pursuant to which we agreed to (i) file a registration statement, or the Resale Registration Statement, with the Securities and Exchange Commission, or SEC, covering the resale of the Old Notes and the underlying common stock into which the Old Notes were convertible upon the written request of Baupost, and (ii) use commercially reasonable efforts, subject to receipt of necessary information from all the purchasers of the Old Notes, to cause the SEC to declare the Resale Registration Statement effective. Further, the Registration Rights Agreement permitted Baupost to demand from time to time that we file a shelf Registration Statement pursuant to Rule 415 of the Securities Act from which any number of shelf takedowns could be conducted upon written request from Baupost. Finally, the Registration Rights Agreement afforded Baupost certain piggyback registration rights. The Old Notes were convertible at the option of Baupost at an initial conversion rate of 267.3797 shares of our common stock per $1,000 principal amount, equal to a conversion price of $3.74 per share, which represented the last reported sale price of our stock on October 14, 2015. The conversion rate was subject to adjustment from time to time upon the occurrence of certain events. Further, upon the occurrence of certain fundamental changes involving us, Baupost could have required us to repurchase for cash all or part of their Old Notes at a repurchase price equal to 100% of the principal amount of the Old Notes to be repurchased. At issuance, a portion of the Old Notes was contingently convertible into cash if our stockholders did not approve an increase in the number of authorized shares of our common stock by July 1, 2016. In accordance with accounting guidance for debt with a conversion option, we separated the conversion option from the debt instrument and accounted for it separately as a derivative liability, due to the Old Notes initially being partially convertible to cash at the option of Baupost. We allocated the proceeds between the debt component and the embedded conversion option (the derivative) by performing a valuation of the derivative as of the transaction date, which was determined based on the difference between the fair value of the Old Notes with the conversion option and the fair value of the Old Notes without the conversion option. The fair value of the derivative liability was recognized as a debt discount and the carrying amount of the Old Notes represented the difference between the proceeds from the issuance of the Old Notes and the fair value of the derivative liability on the date of issuance. The excess of the principal amount of the debt component over its carrying amount, or debt discount, was amortized to interest expense using the effective interest method over the expected life of the debt. Following our 2016 Annual Meeting of Stockholders held on May 25, 2016, we filed a certificate of amendment to our certificate of incorporation with the Secretary of State of the State of Delaware to increase the number of authorized shares of our common stock to allow for the full conversion of the Old Notes into our common stock. On April 10, 2017, we entered into the First Supplemental Indenture, or the First Supplement, to the Indenture. Under the terms of the First Supplement, the Old Notes issued under the Indenture were not convertible by the holders thereof until on or after June 8, 2017, except in connection with a “fundamental change” as defined in the Indenture. After June 8, 2017, the Old Notes were convertible entirely into shares of our common stock or cash depending upon the number of shares of our common stock authorized at the time of such conversion. At our 2017 Annual Meeting of Stockholders held on June 8, 2017, our stockholders ratified the filing and effectiveness of the certificate of amendment to our certificate of incorporation filed in May 2016. In addition, at the meeting our stockholders also approved a separate amendment to our certificate of incorporation to increase the number of authorized shares of our common stock to 230,000,000 shares. As a result, the full amount of the Old Notes was convertible into shares of our common stock. In accordance with accounting guidance for debt modifications and exchanges, we assessed the terms of the First Supplement and determined that it resulted in a modification. During the three months ended June 30, 2017, we separated the conversion option from the debt instrument and accounted for it separately as a derivative liability, due to the Old Notes being contingently convertible to cash at the option of Baupost per the terms of the First Supplement. We allocated the proceeds between the debt component and the embedded conversion option (the derivative) by performing a valuation of the derivative as of the date of the First Supplement, which was determined based on the difference between the fair value of the Old Notes with the conversion option and the fair value of the Old Notes without the conversion option. The fair value of the derivative liability was recognized as a debt discount and the carrying amount of the Old Notes represented the difference between the principal amount of the Old Notes and the fair value of the derivative liability on the date of the First Supplement. The excess of the principal amount of the debt component over its carrying amount, or debt discount, was amortized to interest expense using the effective interest method over the expected life of the debt. We determined the expected life of the debt was equal to the period through June 8, 2017, as this represented the point at which the Old Notes were contingently convertible into cash. On May 8, 2018, we entered into a Notes Exchange Agreement with funds managed by Baupost pursuant to which, on May 9, 2018, we issued $164.746 million of the New Notes to Baupost in exchange for (a) the Old Notes and (b) an additional investment of $10.0 million in cash. The New Notes were issued under an Indenture dated as of May 9, 2018, with The Bank of New York Mellon Trust Company, N.A. as Trustee, or the New Indenture. Under the terms of the New Indenture, the New Notes may be converted into shares of our common stock at the discretion of Baupost, at an initial conversion rate of 215.983 shares per $1,000 principal amount of New Notes, which represents an initial conversion price of $4.63 based on the per share closing price of our common stock the day before entering into the Notes Exchange Agreement. The principal amount of the New Notes initially converts into a total amount of shares of our common stock approximately equal to the 33.4 million shares into which the Old Notes were convertible plus an additional approximately 2.2 million shares in consideration of the additional cash investment. The conversion price of the New Notes is subject to adjustment based on the occurrence of certain events as set forth in the New Indenture. Further, the New Indenture subjects us to certain financial and business covenants. The New Indenture also allows us to secure up to a $40.0 million asset-based credit facility. For a discussion of the credit facility we entered into with Silicon Valley Bank in July 2018, see Note 15 - Subsequent Events. In connection with the issuance of the New Notes, on May 9, 2018, we entered into a Registration Rights Agreement with Baupost, or the New Registration Rights Agreement, on substantially similar terms as the Registration Rights Agreement entered into in connection with the Old Notes, pursuant to which we agreed to (i) file a registration statement (the “Resale Registration Statement”) with the SEC covering the resale of the New Notes and the underlying shares of our common stock upon the written request of Baupost and (ii) use commercially reasonable efforts, subject to the receipt of necessary information from all the purchasers of the New Notes, to cause the SEC to declare the Resale Registration Statement effective. Further, the New Registration Rights Agreement permits Baupost to demand from time to time that we file a shelf Registration Statement pursuant to Rule 415 of the Securities Act, from which any number of shelf takedowns may be conducted upon written request from Baupost. In addition, the New Registration Rights Agreement affords Baupost certain piggyback registration rights. Under the Registration Rights Agreement, Baupost also retains its existing right to appoint one individual to our Board of Directors for so long as Baupost beneficially owns twenty percent (20%) or more of our outstanding common stock and to a board observer for so long as Baupost beneficially owns ten percent (10%) or more of our outstanding common stock. In connection with the issuance of the New Notes, (i) the Notes Purchase Agreement dated as of October 14, 2015 and the Registration Rights Agreement dated as of October 15, 2015, each between us and Baupost were each terminated pursuant to the Notes Exchange Agreement and (ii) the Indenture dated as of October 15, 2015, between us and the Trustee was discharged in connection with the cancellation of the Old Notes. In accordance with accounting guidance for debt modifications and exchanges, we assessed the terms of the Notes Exchange Agreement and New Indenture and determined that they resulted in a modification of our then-existing convertible senior notes. During the three months ended June 30, 2018, we recognized a debt discount of approximately $36.0 million in connection with the modification. The excess of the principal amount of the New Notes over its carrying amount, or debt discount, will be amortized to interest expense using the effective interest method over the expected life of the debt. At issuance of the New Notes, we determined the expected life was equal to the period through the maturity date of the New Notes, or October 2021. In the three and six months ended June 30, 2018 and 2017, $1.3 million and $63.0 million, respectively, of interest expense was recognized related to these notes. As of June 30, 2018 and December 31, 2017, the carrying value of these notes was $130.1 million and $125.0 million, respectively, and the fair value of the Notes was $133.8 million and $155.4 million, respectively. See Note 14 - Strategic Merger with Akebia Therapeutics, Inc. for additional information with respect to the New Notes, and the conversion thereof, related to the Merger.

DEBT

In October 2015, we completed the sale of $125 million of the Old Notes, in a private placement, or the Private Placement, to funds managed by Baupost pursuant to a Notes Purchase Agreement dated October 14, 2015. The Old Notes were issued under an Indenture, or the Indenture, dated as of October 15, 2015, with The Bank of New York Mellon Trust Company, N.A. as trustee, or the Trustee. The Indenture subjected us to certain financial and business covenants and contained restrictions on the payments of cash dividends.

The Indenture contained customary terms and events of default. If an event of default (other than certain events of bankruptcy, insolvency or reorganization involving us) occured and was continuing, the Trustee by notice to us, or the holders of at least 25% in aggregate principal amount of the outstanding Old Notes by written notice to us and the Trustee, could have declared 100% of the principal on all of the Old Notes to be due and payable. Upon such a declaration of acceleration, such principal would be due and payable immediately. Upon the occurrence of certain events of bankruptcy, insolvency or reorganization involving us, 100% of the principal on all of the Old Notes would have become due and payable automatically.

Further, in connection with the Private Placement, we entered into a Registration Rights Agreement with the purchasers of the Old Notes, or the Registration Rights Agreement, pursuant to which we agreed to (i) file a registration statement, or the Resale Registration Statement, with the Securities and Exchange Commission, or SEC, covering the resale of the Old Notes and the underlying common stock into which the Old Notes were convertible upon the written request of Baupost, and (ii) use commercially reasonable efforts, subject to receipt of necessary information from all the purchasers of the Old Notes, to cause the SEC to declare the Resale Registration Statement effective. Further, the Registration Rights Agreement permitted Baupost to demand from time to time that we file a shelf Registration Statement pursuant to Rule 415 of the Securities Act from which any number of shelf takedowns could be conducted upon written request from Baupost. Finally, the Registration Rights Agreement afforded Baupost certain piggyback registration rights.

The Old Notes were convertible at the option of Baupost at an initial conversion rate of 267.3797 shares of our common stock per $1,000 principal amount, equal to a conversion price of $3.74 per share, which represented the last reported sale price of our stock on October 14, 2015. The conversion rate was subject to adjustment from time to time upon the occurrence of certain events. Further, upon the occurrence of certain fundamental changes involving us, Baupost could have required us to repurchase for cash all or part of their Old Notes at a repurchase price equal to 100% of the principal amount of the Old Notes to be repurchased.

At issuance, a portion of the Old Notes was contingently convertible into cash if our stockholders did not approve an increase in the number of authorized shares of our common stock by July 1, 2016. In accordance with accounting guidance for debt with a conversion option, we separated the conversion option from the debt instrument and accounted for it separately as a derivative liability, due to the Old Notes initially being partially convertible to cash at the option of Baupost. We allocated the proceeds between the debt component and the embedded conversion option (the derivative) by performing a valuation of the derivative as of the transaction date, which was determined based on the difference between the fair value of the Old Notes with the conversion option and the fair value of the Old Notes without the conversion option. The fair value of the derivative liability was recognized as a debt discount and the carrying amount of the Old Notes represented the difference between the proceeds from the issuance of the Old Notes and the fair value of the derivative liability on the date of issuance. The excess of the principal amount of the debt component over its carrying amount, or debt discount, was amortized to interest expense using the effective interest method over the expected life of the debt.

Following our 2016 Annual Meeting of Stockholders held on May 25, 2016, we filed a certificate of amendment to our certificate of incorporation with the Secretary of State of the State of Delaware to increase the number of authorized shares of our common stock to allow for the full conversion of the Old Notes into our common stock. On April 10, 2017, we entered into the First Supplemental Indenture, or the First Supplement, to the Indenture. Under the terms of the First Supplement, the Old Notes issued under the Indenture were not convertible by the holders thereof until on or after June 8, 2017, except in connection with a “fundamental change” as defined in the Indenture. After June 8, 2017, the Old Notes were convertible entirely into shares of our common stock or cash depending upon the number of shares of our common stock authorized at the time of such conversion. At our 2017 Annual Meeting of Stockholders held on June 8, 2017, our stockholders ratified the filing and effectiveness of the certificate of amendment to our certificate of incorporation filed in May 2016. In addition, at the meeting our stockholders also approved a separate amendment to our certificate of incorporation to increase the number of authorized shares of our common stock to 230,000,000 shares. As a result, the full amount of the Old Notes was convertible into shares of our common stock.

In accordance with accounting guidance for debt modifications and exchanges, we assessed the terms of the First Supplement and determined that it resulted in a modification. During the three months ended June 30, 2017, we separated the conversion option from the debt instrument and accounted for it separately as a derivative liability, due to the Old Notes being contingently convertible to cash at the option of Baupost per the terms of the First Supplement. We allocated the proceeds between the debt component and the embedded conversion option (the derivative) by performing a valuation of the derivative as of the date of the First Supplement, which was determined based on the difference between the fair value of the Old Notes with the conversion option and the fair value of the Old Notes without the conversion option. The fair value of the derivative liability was recognized as a debt discount and the carrying amount of the Old Notes represented the difference between the principal amount of the Old Notes and the fair value of the derivative liability on the date of the First Supplement. The excess of the principal amount of the debt component over its carrying amount, or debt discount, was amortized to interest expense using the effective interest method over the expected life of the debt. We determined the expected life of the debt was equal to the period through June 8, 2017, as this represented the point at which the Old Notes were contingently convertible into cash.

On May 8, 2018, we entered into a Notes Exchange Agreement with funds managed by Baupost pursuant to which, on May 9, 2018, we issued $164.746 million of the New Notes to Baupost in exchange for (a) the Old Notes and (b) an additional investment of $10.0 million in cash.

The New Notes were issued under an Indenture dated as of May 9, 2018, with The Bank of New York Mellon Trust Company, N.A. as Trustee, or the New Indenture. Under the terms of the New Indenture, the New Notes may be converted into shares of our common stock at the discretion of Baupost, at an initial conversion rate of 215.983 shares per $1,000 principal amount of New Notes, which represents an initial conversion price of $4.63 based on the per share closing price of our common stock the day before entering into the Notes Exchange Agreement. The principal amount of the New Notes initially converts into a total amount of shares of our common stock approximately equal to the 33.4 million shares into which the Old Notes were convertible plus an additional approximately 2.2 million shares in consideration of the additional cash investment. The conversion price of the New Notes is subject to adjustment based on the occurrence of certain events as set forth in the New Indenture. Further, the New Indenture subjects us to certain financial and business covenants. The New Indenture also allows us to secure up to a $40.0 million asset-based credit facility. For a discussion of the credit facility we entered into with Silicon Valley Bank in July 2018, see Note 15 - Subsequent Events.

In connection with the issuance of the New Notes, on May 9, 2018, we entered into a Registration Rights Agreement with Baupost, or the New Registration Rights Agreement, on substantially similar terms as the Registration Rights Agreement entered into in connection with the Old Notes, pursuant to which we agreed to (i) file a registration statement (the “Resale Registration Statement”) with the SEC covering the resale of the New Notes and the underlying shares of our common stock upon the written request of Baupost and (ii) use commercially reasonable efforts, subject to the receipt of necessary information from all the purchasers of the New Notes, to cause the SEC to declare the Resale Registration Statement effective. Further, the New Registration Rights Agreement permits Baupost to demand from time to time that we file a shelf Registration Statement pursuant to Rule 415 of the Securities Act, from which any number of shelf takedowns may be conducted upon written request from Baupost. In addition, the New Registration Rights Agreement affords Baupost certain piggyback registration rights. Under the Registration Rights Agreement, Baupost also retains its existing right to appoint one individual to our Board of Directors for so long as Baupost beneficially owns twenty percent (20%) or more of our outstanding common stock and to a board observer for so long as Baupost beneficially owns ten percent (10%) or more of our outstanding common stock.

In connection with the issuance of the New Notes, (i) the Notes Purchase Agreement dated as of October 14, 2015 and the Registration Rights Agreement dated as of October 15, 2015, each between us and Baupost were each terminated pursuant to the Notes Exchange Agreement and (ii) the Indenture dated as of October 15, 2015, between us and the Trustee was discharged in connection with the cancellation of the Old Notes.

In accordance with accounting guidance for debt modifications and exchanges, we assessed the terms of the Notes Exchange Agreement and New Indenture and determined that they resulted in a modification of our then-existing convertible senior notes. During the three months ended June 30, 2018, we recognized a debt discount of approximately $36.0 million in connection with the modification. The excess of the principal amount of the New Notes over its carrying amount, or debt discount, will be amortized to interest expense using the effective interest method over the expected life of the debt. At issuance of the New Notes, we determined the expected life was equal to the period through the maturity date of the New Notes, or October 2021.

In the three and six months ended June 30, 2018 and 2017, $1.3 million and $63.0 million, respectively, of interest expense was recognized related to these notes. As of June 30, 2018 and December 31, 2017, the carrying value of these notes was $130.1 million and $125.0 million, respectively, and the fair value of the Notes was $133.8 million and $155.4 million, respectively.

See Note 14 - Strategic Merger with Akebia Therapeutics, Inc. for additional information with respect to the New Notes, and the conversion thereof, related to the Merger.