Keryx Biopharmaceuticals (KERX) 10-Q 9 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Trading Symbol	KERX
Entity Registrant Name	KERYX BIOPHARMACEUTICALS INC
Entity Central Index Key	1,114,220
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		120,458,810

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 49,458	$ 93,526
Inventory	48,584	28,695
Accounts receivable, net	15,430	8,146
Other current assets	12,142	11,199
Total current assets	125,614	141,566
Property, plant and equipment, net	4,097	4,521
Goodwill	3,208	3,208
Other assets, net	12,732	9,577
Total assets	145,651	158,872
Current liabilities:
Accounts payable and accrued expenses	54,647	45,031
Deferred lease incentive, current portion	244	244
Other current liabilities	158	145
Total current liabilities	55,049	45,420
Convertible senior notes	130,088	125,000
Deferred lease incentive, net of current portion	895	1,018
Deferred tax liability	0	635
Other liabilities	811	894
Total liabilities	186,843	172,967
Commitments and contingencies
Stockholders’ (deficit) equity:
Preferred stock, $0.001 par value per share (5,000,000 shares authorized, no shares issued and outstanding)	0	0
Common stock, $0.001 par value per share (230,000,000 shares authorized, 120,513,208 and 119,272,304 shares issued, 120,433,260 and 119,192,356 shares outstanding at June 30, 2018 and December 31, 2017, respectively)	120	119
Additional paid-in capital	1,000,381	984,681
Treasury stock, at cost, 79,948 shares	(357)	(357)
Accumulated deficit	(1,041,336)	(998,538)
Total stockholders’ deficit	(41,192)	(14,095)
Total liabilities and stockholders’ deficit	$ 145,651	$ 158,872

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	230,000,000	230,000,000
Common stock, shares issued (in shares)	120,513,208	119,272,304
Common stock, shares outstanding (in shares)	120,433,260	119,192,356
Treasury stock, shares (in shares)	79,948	79,948

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Net U.S. Auryxia product sales	$ 24,105	$ 14,116	$ 44,727	$ 24,621
License revenue	1,644	1,028	2,773	2,343
Total revenues	25,749	15,144	47,500	26,964
Costs and expenses:
Cost of goods sold	7,428	4,379	17,029	8,653
License expense	987	617	1,664	1,406
Research and development	8,774	9,012	17,162	15,776
Selling, general and administrative	28,711	24,986	54,548	48,089
Total costs and expenses	45,900	38,994	90,403	73,924
Operating loss	(20,151)	(23,850)	(42,903)	(46,960)
Other income (expense):
Amortization of debt discount	(1,316)	(62,965)	(1,316)	(62,965)
Other income (expense), net	(51)	338	171	452
Total other income (expense)	(1,367)	(62,627)	(1,145)	(62,513)
Loss before income taxes	(21,518)	(86,477)	(44,048)	(109,473)
Income tax (benefit) expense	0	20	(634)	40
Net loss	$ (21,518)	$ (86,497)	$ (43,414)	$ (109,513)
Basic and diluted net loss per common share (in dollars per share)	$ (0.18)	$ (0.77)	$ (0.36)	$ (1)
Weighted average shares used in computing basic and diluted net loss per common share (in shares)	120,451,534	112,590,188	120,149,604	109,846,152

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net loss	$ (43,414)	$ (109,513)
Adjustments to reconcile net loss to cash flows used in operating activities:
Stock-based compensation expense	8,653	7,336
Amortization of debt discount	1,316	62,965
Change in fair value of derivative liability	0	(225)
Depreciation and amortization	476	459
Amortization of deferred lease incentive	(123)	(122)
Write-down of inventory to net realizable value	5,288	335
Deferred income taxes	(635)	39
Changes in operating assets and liabilities:
Other current assets	598	(5,466)
Accounts receivable, net	(7,284)	(3,223)
Inventory	(24,516)	(4,683)
Other assets	(3,155)	9
Other current liabilities	13	14
Accounts payable and accrued expenses	8,073	7,988
Other liabilities	(83)	(70)
Net cash used in operating activities	(54,793)	(44,157)
Cash flows from investing activities
Purchases of property, plant and equipment	(52)	(420)
Net cash used in investing activities	(52)	(420)
Cash flows from financing activities
Proceeds from issuance of common stock, net of commission	0	73,125
Proceeds from issuance of convertible senior notes	10,000	0
Payments for common stock issuance costs	0	(88)
Proceeds from exercise of stock options	777	257
Net cash provided by financing activities	10,777	73,294
Net (decrease) increase in cash and cash equivalents	(44,068)	28,717
Cash and cash equivalents at beginning of the period	93,526	111,810
Cash and cash equivalents at end of the period	49,458	140,527
Non-cash financing activities:
Change in fair value of conversion feature	6,228	0
Reclassification of derivative liability to equity	$ 0	$ 62,735

Description of Business

Description of Business	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Description of Business	DESCRIPTION OF BUSINESS We are a commercial stage biopharmaceutical company focused on bringing innovative medicines to people with kidney disease. Our long-term vision is to build a multi-product kidney care company. Our marketed product, Auryxia (ferric citrate) tablets, is an orally available, absorbable, iron-based medicine. Auryxia is approved by the U.S. Food and Drug Administration, or FDA, for two indications. Auryxia was originally approved in September 2014 for the control of serum phosphorus levels in patients with chronic kidney disease, or CKD, on dialysis. Additionally, in November 2017, the FDA approved Auryxia for the treatment of iron deficiency anemia in adults with CKD, not on dialysis. With two FDA-approved indications, we will leverage our U.S. clinical and commercial infrastructure to make Auryxia available to millions of people with CKD and either iron deficiency anemia or elevated levels of serum phosphorus, which is referred to as hyperphosphatemia. Ferric citrate is also approved in Japan under the trade name Riona and marketed by our Japanese partner, Japan Tobacco, Inc., or JT, and its subsidiary, Torii Pharmaceutical Co., Ltd., or Torii, and approved in Europe as Fexeric. We use the brand name Auryxia when we refer to ferric citrate for use in the approved indications in the United States. We refer to the product as ferric citrate when referring to its investigational use. Our vision of building a multi-product kidney care company includes expansion of our product portfolio with other medicines that can help patients with kidney disease. On June 28, 2018, we entered into an agreement and plan of merger with Akebia Therapeutics, Inc., or Akebia, a Delaware corporation, and Alpha Therapeutics Merger Sub Inc., a Delaware corporation and wholly-owned subsidiary of Akebia, or Merger Sub, pursuant to which we will combine our respective businesses through the merger of Merger Sub with and into us, with our company continuing after such merger as the surviving corporation and a wholly-owned subsidiary of Akebia, or the Merger. For additional details regarding the Merger, see Note 14 - Strategic Merger with Akebia Therapeutics, Inc.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited condensed consolidated financial statements were prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they may not include all of the information and footnotes required by GAAP for complete financial statements. All adjustments that are, in the opinion of management, of a normal recurring nature and are necessary for a fair presentation of these interim financial statements have been included. These interim condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements contained in our Annual Report on Form 10-K for the year ended December 31, 2017 . The year-end condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by GAAP. The results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the entire fiscal year or any other interim period. Principles of Consolidation The condensed consolidated financial statements include our financial statements and those of our wholly-owned subsidiaries. Intercompany transactions and balances have been eliminated in consolidation. Use of Estimates The preparation of our condensed consolidated financial statements, which have been prepared in accordance with GAAP requires us to make estimates, judgments and assumptions that affect the reported amounts of assets, liabilities, equity revenue and expenses and related disclosure of contingent assets and liabilities. On an ongoing basis, we evaluate our estimates, judgments and assumptions. We base our estimates on historical experience, known trends and events and various other factors that we believe to be reasonable under the circumstances. These estimates are subject to an inherent degree of uncertainty, and as a result, actual results may differ from these estimates under different assumptions or conditions. Revenue Recognition Effective January 1, 2018, we adopted Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606) , using the modified retrospective transition method. Under this transition method, we will not revise our consolidated financial statements for the years ended December 31, 2017 and 2016, and applicable interim periods within those years. Disclosure will be provided to show the impact to the consolidated financial statements, if any, as if ASU, 2014-09 had been effective for those periods. Our primary source of revenue during the reporting periods was product sales. We sell product to a limited number of major wholesalers, or our Distributors, as well as certain pharmacies, or collectively with our Distributors, our Customers. Our Distributors resell the product to retail pharmacies for purposes of their reselling the product to fill patient prescriptions. Under the new revenue standards, we recognize product revenue when our Customer obtains control of promised goods, in an amount that reflects the consideration which we expect to receive in exchange for those goods. We recognize revenue following the five step model prescribed under ASU No. 2014-09: (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) we satisfy the performance obligation. Product Revenue: We sell product to a limited number of our Distributors as well as certain specialty pharmacies. Our Distributors resell the product to retail pharmacies for purposes of filling patient prescriptions. In addition to agreements with Customers, we enter into arrangements with health care providers and payors that provide for government-mandated or privately-negotiated discounts and rebates with respect to the purchase of our product. Revenue from product sales are recognized when the Customer obtains control of our product, which occurs at a point in time, typically upon delivery to the Customer. We expense incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that we would have recognized is one year or less. Reserves for Discounts and Allowances: Revenue from product sales are recorded at the transaction price, which is equal to the sales price net of reserves for discounts and allowances that are offered within contracts with our Customers, health care providers, payors or other indirect customers. These discounts and allowances represent variable consideration under the new revenue standards. Our process for estimating these components of variable consideration do not differ materially from our historical practices. Product revenue reserves are classified as a reduction in product revenue and are generally characterized in the following categories: trade allowances, rebates and chargebacks, product returns and other incentives. These reserves are based on estimates of the amounts earned or to be claimed on the related sale of product and are classified as either a reduction of accounts receivable or an accrued expense (current liability) on our consolidated balance sheets, depending on whether the consideration is paid to a direct customer or another third party with which we contract (e.g. provider or payor) and the method of payment. Our estimates of reserves for variable consideration typically utilize the most likely method and reflect our historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Our product revenue reserves reflect our best estimates of the amount of consideration to which we are entitled based on the terms of the individual contracts. The transaction price, which includes variable consideration reflecting the impact of discounts and allowances, may be subject to constraint and is included in the net sales price only to the extent that it is probable that a significant reversal of the amount of the cumulative revenues recognized will not occur in a future period. Actual amounts may ultimately differ from our estimates. If actual results vary, we adjust these estimates, which could have an effect on earnings in the period of adjustment. License Revenue: Our license revenue consists of license fees, royalties and milestone payments arising from our agreement with JT and Torii. We receive royalty revenues on sales by JT and Torii of Riona in Japan. We do not have future performance obligations under this license arrangements. We record these royalty revenues based on estimates of the net sales that occurred during the relevant period as license revenue. The relevant period estimate of sales is based on analysis of historical royalties that have been paid to us, adjusted for any changes in facts and circumstances, as appropriate. Differences between actual and estimated royalty revenues are adjusted in the period in which they become known, typically the following quarter. Disaggregation of Revenue Currently, our only product is Auryxia, which we commercialize only in the United States. We have no foreign operations; however, we currently generate license revenue based on net sales of Riona by our partner in Japan, as discussed above. License revenue for all periods presented represents royalty revenue generated from our sublicense agreement with JT and Torii. Significant Judgments Our revenue reserves, consisting of various discounts and allowances, which are components of variable consideration as discussed above, are considered an area of significant judgment. Additionally, our license revenue in each period, as discussed above, is based on estimates of the net sales of our Japanese partner that occurred during the relevant period. The relevant period estimate of sales is based on analysis of historical royalties that have been paid to us, adjusted for any changes in facts and circumstances, as appropriate, and is considered an area of significant judgment. For these areas of significant judgment, actual amounts may ultimately differ from our estimates and are adjusted in the period in which they become known. Practical Expedients Significant financing component : Our accounts receivable arise from product sales and primarily represent amounts due from our wholesale and other third-party distributors. We do not adjust our receivables for the effects of a significant financing component at contract inception if we expect to collect the receivables in one year or less from the time of sale. Cost to obtain a contract : We recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that we otherwise would have recognized is one year or less or the amount is immaterial. Sales taxes : Taxes collected from Customers relating to product sales and remitted to governmental authorities, if any, are excluded from revenues. Our U.S. Auryxia product sales for the three and six months ended June 30, 2018 and 2017 were offset by provisions for allowances and accruals as set forth in the tables below. (in thousands) Three months ended Percent of gross Auryxia product sales Three months ended Percent of gross Auryxia product sales Gross Auryxia product sales $ 46,821 $ 26,029 Less provision for product sales allowances and accruals: Trade allowances 4,957 11% 2,463 9% Rebates, chargebacks and discounts 16,135 35% 8,784 34% Product returns 572 1% 346 2% Other incentives (1) 1,052 2% 320 1% Total 22,716 49% 11,913 46% Net U.S. Auryxia product sales $ 24,105 $ 14,116 (1) Includes co-pay assistance and voucher rebates. (in thousands) Six months ended June 30, 2018 Percent of gross Six months ended June 30, 2017 Percent of gross Gross Auryxia product sales $ 87,960 $ 43,983 Less provision for product sales allowances and accruals: Trade allowances 9,140 10% 4,228 9% Rebates, chargebacks and discounts 30,928 35% 14,114 32% Product returns 736 1% 278 1% Other incentives (1) 2,429 3% 742 2% Total 43,233 49% 19,362 44% Net U.S. Auryxia product sales $ 44,727 $ 24,621 (1) Includes co-pay assistance and voucher rebates. Basic and Diluted Net Loss Per Common Share Basic net loss per share is computed by dividing the losses allocable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss per share does not reflect the effect of shares of common stock to be issued upon the exercise of stock options, as their inclusion would be anti-dilutive. The following table presents amounts that were excluded from the calculation of diluted net loss per share, due to their anti-dilutive effect: (in thousands) June 30, 2018 June 30, 2017 Options to purchase common stock 11,044 12,469 Shares issuable upon conversion of convertible senior notes 35,582 33,422 Shares issuable under Notes Conversion Agreement (1) 4,000 — 50,626 45,891 (1) See Note 14 - Strategic Merger with Akebia Therapeutics, Inc. Concentrations of Credit Risk We do not have significant off-balance sheet risk or credit risk concentrations. We maintain our cash and cash equivalents with multiple financial institutions. As of June 30, 2018 , approximately $2.0 million of our total $49.5 million cash and cash equivalents balance was invested in institutional money market funds. See Note 3 – Fair Value Measurements . Our accounts receivable, net at June 30, 2018 and December 31, 2017 represent amounts due to us from our Customers. We perform ongoing credit evaluations of our Customers and generally do not require collateral. The following table sets forth Customers who represented 10% or more of our total accounts receivable, net as of June 30, 2018 and December 31, 2017 . June 30, 2018 December 31, 2017 Fresenius Medical Care Rx 29 % 34 % AmerisourceBergen Drug Corporation 20 % 20 % Cardinal Health, Inc. 17 % 25 % DaVita Rx 16 % — % McKesson Corporation 14 % 17 % New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or the FASB, or other standard setting bodies that we adopt as of the specified effective date. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , a comprehensive new standard which amends revenue recognition principles and provides a single set of criteria for revenue recognition among all industries. The new standard provides a five-step framework whereby revenue is recognized when promised goods or services are transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires enhanced disclosures pertaining to revenue recognition in both interim and annual periods. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The FASB has subsequently issued amendments to ASU No. 2014-09 that have the same effective date and transition date: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations ; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing ; ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients ; and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers . We adopted these amendments with ASU 2014-09, or collectively, the new revenue standards. The new revenue standards became effective for us on January 1, 2018 and were adopted using the modified retrospective method. The adoption of the new revenue standards did not have a material impact on our revenue recognition as the majority of our revenues continue to be recognized when the Customer takes control of our product. However, the adoption of the new revenue standards did result in an adjustment to retained earnings (accumulated deficit) as of the adoption date of $0.6 million related to our license revenue and related license expense. See Note 8 – License Agreements for further discussion. Under the new revenue standards, we recognize revenues when our Customer obtains control of promised goods, in an amount that reflects the consideration which we expect to receive in exchange for those goods. We recognize revenues following the five step model prescribed under ASU No. 2014-09: (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) we satisfy the performance obligation. In February 2016, the FASB issued ASU No. 2016-02, Leases . The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The new standard will be effective for us on January 1, 2019 and is required to be applied using a modified retrospective transition approach with application of the new guidance for all periods presented. We are in the process of reviewing contracts with our contract manufacturers to determine whether these agreements contain any potential embedded leases. Although our assessment is not complete, we currently expect the adoption of this guidance to result in the addition of material balances of leased assets and corresponding lease liabilities to our consolidated balance sheets. We do not currently expect a material impact to our consolidated statements of operations as a result of this standard. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . The new standard addresses eight specific cash flow issues with the objective of reducing the existing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The new standard was effective for us on January 1, 2018. The standard did not have a material impact on our consolidated statements of cash flows upon adoption.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The following table provides the fair value measurements of applicable financial assets as of June 30, 2018 and December 31, 2017 : Financial assets at fair value Financial assets at fair value (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets: Cash equivalents (1) $ 2,010 $ — $ — $ 1,895 $ — $ — Total assets $ 2,010 $ — $ — $ 1,895 $ — $ — (1) Cash equivalents as of June 30, 2018 and December 31, 2017 consisted of institutional money market funds. The carrying value of our money market funds approximates fair value due to their short-term maturities. Debt In October 2015, we issued $125 million in Convertible Senior Notes, due 2020, or the Old Notes, in a private financing to funds managed by Baupost Group Securities, L.L.C., or Baupost. On May 8, 2018, we entered into a Notes Exchange Agreement, or the Notes Exchange Agreement, with funds managed by Baupost pursuant to which, on May 9, 2018, we issued $164.746 million of Convertible Senior Notes due 2021, or the New Notes, to Baupost in exchange for (a) the Old Notes, and (b) an additional investment of $10.0 million in cash. As of December 31, 2017 , the fair value of the Old Notes was $155.4 million and, as of June 30, 2018 , the fair value of the New Notes was $133.8 million , not including the additional 4.0 million shares that may be issued under the Notes Conversion Agreement, which in each case differs from their carrying value. The fair value of these notes is influenced by our stock price and stock price volatility. See Note 10 – Debt and Note 14 – Strategic Merger with Akebia Therapeutics, Inc. for additional information on our debt obligations.

Inventory

Inventory	6 Months Ended
	Jun. 30, 2018
Inventory Disclosure [Abstract]
Inventory	INVENTORY Inventory consists of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Raw materials $ 1,493 $ 469 Work in process 43,761 25,160 Finished goods 3,330 3,066 Total inventory $ 48,584 $ 28,695 We wrote off approximately $1.2 million and $0.3 million of inventory that was determined to no longer be suitable for commercial manufacture, which was recorded to cost of goods sold during the three months ended June 30, 2018 and June 30, 2017 , respectively, and $5.3 million and $0.3 million during the six months ended June 30, 2018 and June 30, 2017 , respectively.

Other Assets

Other Assets	6 Months Ended
	Jun. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Assets	OTHER ASSETS Other current assets Other current assets consisted of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Prepaid manufacturing costs $ 7,121 $ 7,646 Prepaid selling, general and administrative expenses 3,616 2,265 Prepaid research and development expenses 1,405 1,288 Total other current assets $ 12,142 $ 11,199 Prepaid manufacturing costs as of June 30, 2018 and December 31, 2017 primarily relate to upfront payments to our contract manufacturers related to 2018 production of inventory. Other assets, net Other assets, net consisted of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Deferred manufacturing costs $ 10,433 $ 7,338 Deposits 1,159 1,099 Long-term prepaid manufacturing costs 1,000 1,000 Deferred registration fees 140 140 Total other long-term assets $ 12,732 $ 9,577 Deferred manufacturing costs as of June 30, 2018 and December 31, 2017 consisted of amounts paid or payable under contract manufacturing agreements, including a $5.0 million milestone related to a facility construction agreement and $2.4 million and $2.3 million in product premiums payable by us to our contract manufacturer at June 30, 2018 and December 31, 2017, respectively. We capitalize certain expenses as deferred costs related to agreements with contract manufacturers in connection with the facility expansion activities. These costs will be capitalized as incurred and will begin to be expensed at such time that we begin to receive product from the newly-constructed or expanded facilities. These costs will be expensed ratably over the relevant supply periods based on anticipated product to be received from the facilities. At June 30, 2018 and December 31, 2017 , zero and $7.3 million , respectively, included in deferred manufacturing costs were also recorded as a liability on our consolidated balance sheets as they had not yet been paid.

Stockholders' Deficit

Stockholders' Deficit	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stockholders' Deficit	STOCKHOLDERS’ DEFICIT Change in Stockholders’ Deficit Total stockholders’ deficit was $41.2 million at June 30, 2018 , which is an increase of $27.1 million as compared to stockholders’ deficit at December 31, 2017 of $14.1 million . This increase was primarily attributable to our net loss of approximately $43.4 million for the six months ended June 30, 2018 , partially offset by $8.7 million related to stock-based compensation expense, $6.2 million related to the recognition of an additional debt discount recorded in connection with the modification of our senior convertible notes and $0.6 million related to an adjustment to accumulated deficit as of January 1, 2018 upon the adoption of ASU 2014-09. See Note 8 - License Agreements for further discussion related to the adjustment recorded.

Stock-Based Compensation Expens

Stock-Based Compensation Expense	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Expense	STOCK-BASED COMPENSATION EXPENSE Equity Incentive Plans As of June 30, 2018 , a total of 7,768,360 shares were available for the issuance of stock options or other stock-based awards under our stock option and incentive plans. Stock Options The following table summarizes stock option activity for the six months ended June 30, 2018 : Number of shares Weighted average exercise price Outstanding at December 31, 2017 11,967,815 $ 6.73 Granted 980,000 4.11 Exercised (204,521 ) 3.80 Forfeited or Expired (1,699,249 ) 5.85 Outstanding at June 30, 2018 11,044,045 $ 6.68 Vested and expected to vest at June 30, 2018 8,917,383 $ 6.93 Exercisable at June 30, 2018 5,809,968 $ 8.00 Upon the exercise of stock options, we issue new shares of our common stock. As of June 30, 2018 , 3,177,500 options issued to employees are unvested, performance-based options. Restricted Stock Certain employees and directors have been awarded restricted stock under our equity incentive plans. The time-vesting restricted stock awards vest primarily over a period of three years. The following table summarizes restricted share activity for the six months ended June 30, 2018 : Number of shares Weighted average grant date fair value Outstanding at December 31, 2017 1,884,297 $ 6.39 Granted 1,523,650 4.45 Vested (598,170 ) 5.62 Forfeited (487,267 ) 4.90 Outstanding at June 30, 2018 2,322,510 $ 5.63 As of June 30, 2018 , 310,000 shares of restricted stock issued to employees are unvested, performance-based shares. Stock-Based Compensation Expense We incurred $5.0 million and $3.7 million of stock-based compensation expense related to equity incentive grants during the three months ended June 30, 2018 and 2017 , respectively, and $8.7 million and $7.3 million during the six months ended June 30, 2018 and 2017 , respectively. The following table reflects stock-based compensation expense for the three and six months ended June 30, 2018 and 2017 : Three months ended June 30, Six months ended June 30, (in thousands) 2018 2017 2018 2017 Cost of goods sold $ 25 $ 28 $ 43 $ 88 Research and development 570 483 1,312 1,061 Selling, general and administrative 4,377 3,161 7,298 6,187 Total stock-based compensation expense $ 4,972 $ 3,672 $ 8,653 $ 7,336 Stock-based compensation costs capitalized as part of inventory were immaterial for the three and six months ended June 30, 2018 and 2017 . The fair value of stock options granted is estimated at the date of grant using the Black-Scholes pricing model. The expected term of options granted is derived from historical data, the expected vesting period and the full contractual term. Expected volatility is based on the historical volatility of our common stock. The risk-free interest rate is based on the U.S. Treasury Yield for a period consistent with the expected term of the option in effect at the time of the grant. We have assumed no expected dividend yield, as dividends have never been paid to stock or option holders and will not be paid for the foreseeable future. The weighted average grant date fair value of stock options granted during the three months ended June 30, 2018 and 2017 was $2.42 and $4.65 per share, respectively, and during the six months ended June 30, 2018 and 2017 was $2.87 and $3.86 per share, respectively. We use historical information to estimate forfeitures of stock-based awards. As of June 30, 2018 , there was $9.2 million and $8.1 million of total unrecognized compensation cost related to non-vested stock options and restricted stock, respectively, which is expected to be recognized over weighted-average periods of 2.2 years and 1.9 years , respectively. These amounts do not include 3,177,500 unvested options and 310,000 shares of unvested restricted stock as of June 30, 2018 which are performance-based and vest upon achievement of certain corporate milestones. Stock-based compensation for these awards will be measured and recorded if and when it is probable that the milestone will be achieved.

License Agreements

License Agreements	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License Agreements	LICENSE AGREEMENTS In November 2005, we entered into a license agreement with Panion & BF Biotech, Inc., or Panion. Under the license agreement, we acquired the exclusive worldwide rights, excluding certain Asian-Pacific countries, for the development and marketing of ferric citrate. To date, we have paid an aggregate of $11.6 million of milestone payments to Panion. In addition, Panion is eligible to receive royalty payments based on a mid-single digit percentage of net sales of ferric citrate. In September 2007, we entered into a Sublicense Agreement with JT and Torii, under which JT and Torii obtained the exclusive sublicense rights for the development and commercialization of ferric citrate in Japan, which is being marketing in the United States under the trade name Auryxia. JT and Torii are responsible for the future development and commercialization costs in Japan. Effective as of June 8, 2009, we entered into an Amended and Restated Sublicense Agreement with JT and Torii, which, among other things, provided for the elimination of all significant on-going obligations under the Sublicense Agreement. In January 2013, JT and Torii filed its new drug application with the Japanese Ministry of Health, Labour and Welfare for marketing approval of ferric citrate in Japan for the treatment of hyperphosphatemia in patients with CKD. In January 2014, JT and Torii received manufacturing and marketing approval of ferric citrate from the Japanese Ministry of Health, Labour and Welfare. Ferric citrate, launched in May 2014 and is being marketed in Japan by Torii, under the brand name Riona, and is indicated as an oral treatment for the improvement of hyperphosphatemia in patients with CKD. We receive royalty payments based on a tiered double-digit percentage of net sales of Riona in Japan escalating up to the mid-teens, as well as up to an additional $55.0 million upon the achievement of certain annual net sales milestones. We assessed the sublicense agreement in accordance with ASU 2014-09 and concluded that the contract counterparties, JT and Torii, are a customer. As of the adoption date of January 1, 2018, the sublicense represents our only open contract with a customer. The primary performance obligation identified in the contract is the sublicense to JT and Torii for the right to develop and commercialize ferric citrate in the licensed territory, Japan. Other potential performance obligations identified were either completed before the adoption date or did not meet the definition of a performance obligation, for instance because they were not capable of being distinct within the context of the contract, and therefore were not required to be accounted for separately. In determining the transaction price associated with the sublicense, we considered the initial license fee as well as any development-based milestones, manufacturing fee revenue, and sales-based royalties and milestones that were included in the arrangement. The performance obligations related to the initial license fee, development-based milestones and manufacturing fee revenue were all completed and the relevant consideration was received prior to the adoption of the new standards. As a result, we determined that the remaining consideration that may be payable to us under the terms of the sublicense agreement are either quarterly royalties on net sales or payments due upon the achievement of sales-based milestones. In accordance with the standards, elements of consideration subject to a sales or usage-based royalty exception do not need to be estimated at the time of adoption and should be recognized when the subsequent sale or usage occurs. As a result, as of January 1, 2018, we began recognizing license revenue based on our estimate of net sales of Riona in Japan in the quarter in which the underlying net sales occur. This differs from our historical practice of recognizing license revenue one quarter in arrears once a net sales report was received from JT and Torii. As a result of this change in timing of revenue recognition for license revenue, we recorded an adjustment of $0.6 million to retained earnings (accumulated deficit) as of the adoption date, representing the net impact to our statement of operations of the license revenue and related license expense based on net sales of Riona in Japan during the fourth quarter of 2017. As discussed above and in accordance with our revenue recognition policy, royalty revenues are estimated in the quarter that JT and Torii recognize net sales of Riona in Japan. Any difference between the estimated license revenue and actual revenue is recorded as an adjustment in the following reporting period. For the three months ended June 30, 2018 and 2017 , we recorded $1.6 million and $1.0 million , respectively, in license revenue related to royalties earned on net sales of Riona in Japan. For the six months ended June 30, 2018 and 2017 , we recorded $2.8 million and $2.3 million , respectively, in license revenue related to royalties earned on net sales of Riona in Japan. We record the associated mid-single digit percentage of net sales royalty expense due Panion, the licensor of ferric citrate, in the same period as the royalty revenue from JT and Torii is recorded. For the three months ended June 30, 2018 and 2017 , we recorded $1.0 million and $0.6 million , respectively, in license expense related to royalties due to the licensor of ferric citrate relating to sales of Riona in Japan. For the six months ended June 30, 2018 and 2017 , we recorded $1.7 million and $1.4 million , respectively, in license expense related to royalties due to the licensor of ferric citrate relating to sales of Riona in Japan.

Accounts Payable And Accrued Ex

Accounts Payable And Accrued Expenses	6 Months Ended
	Jun. 30, 2018
Payables and Accruals [Abstract]
Accounts Payable And Accrued Expenses	ACCOUNTS PAYABLE AND ACCRUED EXPENSES Accounts payable and accrued expenses consists of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Commercial rebates and fees $ 21,056 $ 16,362 Accounts payable 17,582 6,474 Professional, license, and other fees and expenses 9,252 5,257 Accrued compensation and related liabilities 5,994 7,504 Accrued manufacturing expenses 763 9,434 Total accounts payable and accrued expenses $ 54,647 $ 45,031

Debt

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.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES In December 2017, H.R.1, known as the Tax Cuts and Jobs Act, was signed into law. The Tax Cuts and Jobs Act, among other items, reduced the corporate income tax rate from 35% to 21%, effective January 1, 2018. Our deferred tax assets, net of deferred tax liabilities, represent expected corporate tax benefits anticipated to be realized in the future. The reduction in the federal corporate tax rate reduces these benefits. We have evaluated the impact of the Tax Cuts and Jobs Act and determined that any net operating losses generated subsequent to January 1, 2018 are able to be used indefinitely, and as a result, we generated sufficient net operating losses in the six months ended June 30, 2018 to fully offset the net deferred tax liability that was recorded on our consolidated balance sheets. This results in a reduction in our net deferred tax liability of $0.6 million in the first quarter of 2018 and a corresponding $0.6 million income tax benefit. We account for income taxes under the asset and liability method. Deferred tax assets and liabilities are determined based on differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is established when necessary to reduce deferred tax assets to the amount expected to be realized. In determining the need for a valuation allowance, management reviews both positive and negative evidence, including current and historical results of operations, future income projections and the overall prospects of our business. Based upon management’s assessment of all available evidence, we believe that it is more-likely-than-not that the deferred tax assets will not be realizable; and therefore, a full valuation allowance is established.

Other Income (Expense), Net

Other Income (Expense), Net	6 Months Ended
	Jun. 30, 2018
Other Income and Expenses [Abstract]
Other Income (Expense), Net	OTHER INCOME (EXPENSE), NET The components of other income (expense), net are as follows: Three months ended June 30, Six months ended June 30, (in thousands) 2018 2017 2018 2017 Interest income $ 179 $ 118 $ 380 $ 235 Other income (expense) (230 ) (5 ) (209 ) (8 ) Fair value adjustment to derivative liability — 225 — 225 Total other income (expense), net $ (51 ) $ 338 $ 171 $ 452

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Commitments As of June 30, 2018 , our contractual obligations and commitments primarily consist of our obligations under non-cancelable leases, the New Notes and various agreements with third parties, including selling, general and administrative, research and development and manufacturing agreements. Contingencies We accrue a liability for legal contingencies when we believe that it is both probable that a liability has been incurred and that we can reasonably estimate the amount of the loss. We review these accruals and adjust them to reflect the best information available at the time. To the extent new information is obtained and our views on the probable outcomes of claims, suits, assessments, investigations or legal proceedings change, changes in our accrued liabilities would be recorded in the period in which such determination is made. For the matters referenced below, a liability is not probable or the amount cannot be reasonably estimated and, therefore, an accrual has not been made. In addition, in accordance with the relevant authoritative guidance, for any matters in which the likelihood of material loss is at least reasonably possible, we will provide disclosure of the possible loss or range of loss. If a reasonable estimate cannot be made, however, we will provide disclosure to that effect. We expense legal costs as they are incurred. Four purported class action lawsuits have been filed against us and certain of our current and former officers (Gregory P. Madison, Scott A. Holmes, Ron Bentsur, and James Oliviero). Three of these actions were filed in the U.S. District Court for the Southern District of New York, captioned respectively Terrell Jackson v. Keryx Biopharmaceuticals, Inc., et al., No. 1:16-cv-06131, filed on August 2, 2016, Richard J. Erickson v. Keryx Biopharmaceuticals, Inc., et al. No. 1:16-cv-06218, filed on August 4, 2016, and Richard King v. Keryx Biopharmaceuticals, Inc., et al., No. 1:16-cv-06233, filed on August 5, 2016. The Jackson complaint purports to be brought on behalf of stockholders who purchased our common stock between February 25, 2016 and August 1, 2016, the Erickson complaint purports to be brought on behalf of stockholders who purchased our common stock between March 2, 2016 and July 29, 2016, and the King complaint purports to be brought on behalf of stockholders who purchased our common stock between February 25, 2016 and July 29, 2016. On August 26, 2016, the fourth complaint, captioned Tim Karth v. Keryx Biopharmaceuticals, Inc., et al., No. 1:16-cv-11745, was filed in the U.S. District Court for the District of Massachusetts, which complaint was subsequently amended. The Karth complaint purports to be brought on behalf of stockholders who purchased our common stock between May 8, 2013 and August 1, 2016. The Jackson, Erickson and King matters were transferred to the U.S. District Court for the District of Massachusetts on April 5, 2017 and subsequently consolidated with the Karth action. Each complaint generally alleges that we and certain of our current and former officers violated Sections 10(b) and/or 20(a) of the Exchange Act and Rule 10b-5 promulgated thereunder by making allegedly false and/or misleading statements concerning us and our business operations and future prospects in light of the August 1, 2016 announcement of an interruption in our supply of Auryxia. By order dated July 19, 2018, the Court granted in part and denied in part Defendants’ motion to dismiss the complaint. On August 2, 2018, Defendants filed an answer to the complaint and a motion for partial reconsideration of the Court’s July 19, 2018 order. Two stockholder derivative complaints were also filed on December 16, 2016 against us and certain of our current and former officers (Gregory P. Madison, Scott A. Holmes, Ron Bentsur and James Oliviero), certain of our current directors (Kevin J. Cameron, Daniel P. Regan, Steven C. Gilman and Michael Rogers ) and our former directors (Michael P. Tarnok, Joseph Feczko, Jack Kaye Wyche Fowler, Jr. and John P. Butler), in the Superior Court of Massachusetts, one captioned Venkat Vara Prasad Malledi v. Keryx Biopharmaceuticals, Inc., et al., No. 16-3865 and one captioned James Anderson v. Keryx Biopharmaceuticals, Inc., et al., No. 16-3866. Each of these two complaints generally allege that the individual defendants breached their fiduciary duties owed to us, unjustly enriched themselves by their actions, abused their control positions with us, mismanaged us and wasted corporate assets since July 31, 2013 in light of our August 1, 2016 announcement by us of an interruption in the supply of our product Auryxia. On June 27, 2017, the Superior Court granted the parties' motion to consolidate and stay the derivative litigations. All of the complaints seek unspecified damages, interest, attorneys’ fees, and other costs. We deny any allegations of wrongdoing and intend to vigorously defend against these lawsuits. There is no assurance, however, that we or the other defendants will be successful in our defense of either of these lawsuits or that insurance will be available or adequate to fund any settlement or judgment or the litigation costs of these actions. Moreover, we are unable to predict the outcome or reasonably estimate a range of possible losses at this time. A resolution of these lawsuits adverse to us or the other defendants, however, could have a material effect on our financial position and results of operations in the period in which the particular lawsuit is resolved.

Strategic Merger with Akebia Th

Strategic Merger with Akebia Therapeutics, Inc.	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Strategic Merger with Akebia Therapeutics, Inc.	STRATEGIC MERGER WITH AKEBIA THERAPEUTICS, INC. Agreement and Plan of Merger On June 28, 2018, we entered into an agreement and plan of merger, or the Merger Agreement, with Akebia and Merger Sub, pursuant to which we will combine our respective businesses through the merger of Merger Sub with and into us, with our Company continuing after the Merger as the surviving corporation and a wholly-owned subsidiary of Akebia. The Merger Agreement has been approved by our Board of Directors and the board of directors of Akebia. At the effective time of the Merger, (i) each share of our common stock issued and outstanding immediately prior to the effective time of the Merger (other than the shares that are held by Akebia, Merger Sub, any subsidiary of Akebia or us, or held by us as treasury shares) will be converted into and become 0.37433 fully paid and non-assessable shares of common stock of Akebia, $0.00001 par value per share, each, an Akebia Share, such that the pre-Merger stockholders of us and Akebia will each own approximately 50% of the voting power of the combined company upon the closing of the Merger, which we refer to as the Combined Company, based on each of the companies’ fully diluted market capitalizations as of signing and before taking into account the 4.0 million additional shares issuable to Baupost described below. The Merger Agreement provides that, at the effective time of the Merger, each of our outstanding restricted shares issued under our equity incentive plans, which we refer to as Restricted Shares, other than those Restricted Shares that accelerate or lapse as a result of the Merger, will be canceled and converted into restricted stock unit awards of Akebia, the number of which will be adjusted in accordance with the terms of the Merger Agreement. Each of those Restricted Shares whose restrictions (including vesting) accelerate or lapse as a result of the Merger, will be canceled and converted into the right to receive 0.37433 Akebia Shares. In addition, each outstanding and unexercised option to acquire shares of our common stock granted under our equity incentive plans will be canceled and converted into an option to acquire Akebia Shares, with the number of shares and exercise price adjusted for the exchange ratio in accordance with the terms of the Merger Agreement. The Combined Company is expected to have a board of directors consisting initially of nine directors, comprised of: (i) four directors designated by the current board of directors of Akebia, each of whom will be a director of Akebia immediately prior to the date of the Merger Agreement (and who will be reasonably acceptable to us), referred to as the Akebia Directors; (ii) four directors designated by our current Board of Directors, each of whom will be a director of ours immediately prior to the date of the Merger Agreement (and who will be reasonably acceptable to Akebia), referred to as the Keryx Directors; and (iii) one additional director to be designated by our Board of Directors, who will serve as the chairperson and be reasonably acceptable to Akebia, referred to as the Additional Director. Alternatively, the Keryx Directors may choose to select the chairperson from amongst the Keryx Directors, who will be reasonably acceptable to Akebia, and in such an event such Keryx Director will serve as chairperson and the Akebia Directors and the Keryx Directors will select the Additional Director, who will be a person not on either the board of directors of Akebia or our Board of Directors as of the date of the Merger Agreement. We and Akebia each made certain representations and warranties, and agreed to certain covenants, in the Merger Agreement, including covenants by Akebia and us to conduct the respective businesses in the ordinary course during the period between the execution of the Merger Agreement and consummation of the Merger, to refrain from taking certain actions specified in the Merger Agreement and to use reasonable best efforts to cause the conditions of the Merger to be satisfied. The consummation of the Merger is subject to customary closing conditions, including: (i) approval of the issuance of Akebia Shares in connection with the Merger by the affirmative vote of the majority of Akebia Shares cast at the Akebia shareholders’ meeting in favor of the issuance of Akebia Shares in connection with the Merger; (ii) the adoption of the Merger Agreement by the affirmative vote of the holders of a majority of all outstanding shares of Keryx common stock entitled to vote thereon; (iii) the absence of any adverse law or order promulgated, entered, enforced, enacted or issued by any governmental entity that prohibits, restrains or makes illegal the consummation of the Merger; (iv) the Akebia Shares to be issued in the Merger being approved for listing on the Nasdaq Global Market; (v) the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 and other material government approvals; (vi) subject to certain materiality exceptions, the accuracy of certain representations and warranties of each of us and Akebia contained in the Merger Agreement and the compliance by each party with the covenants contained in the Merger Agreement; and (vii) the absence of a material adverse effect with respect to each of us and Akebia. Akebia’s obligation to consummate the Merger is also subject to the conversion of the New Notes into shares of our common stock before the closing of the Merger pursuant to the Notes Conversion Agreement described below. We expect the Merger will be completed in the second half of 2018. The Merger Agreement contains certain termination rights for both us and Akebia, including for the failure to consummate the Merger by December 28, 2018, the enactment, promulgation or issuance of any injunction, order or ruling which has become final and non-appealable and makes the consummation of the Merger illegal or otherwise prohibits consummation of the Merger, failure of either our stockholders or Akebia’s stockholders to approve the Merger and related transactions, or breaches of representations, warranties or covenants by a party that result in the failure of certain conditions to closing being satisfied. In addition, each of us and Akebia have the right to terminate the Merger Agreement in order to enter into a “Superior Proposal” (as defined in the Merger Agreement). Upon termination of the Merger Agreement under certain specified circumstances Akebia or we may be required to pay the other party a termination fee of $22.0 million . Notes Conversion Transactions In connection with the Merger, we entered into a Notes Conversion Agreement, or the Conversion Agreement, with Baupost and, with respect to certain sections only, Akebia. Pursuant to the terms of the Conversion Agreement, Baupost has agreed to convert the New Notes into the 35.6 million shares of our common stock into which the New Notes are currently convertible, immediately prior to the effective time of the Merger, conditioned upon our issuance to Baupost of an additional 4.0 million shares of our common stock.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS Entry Into A Material Definitive Agreement On July 18, 2018, we entered into a Loan and Security Agreement with Silicon Valley Bank, or SVB, pursuant to which SVB made a revolving line of credit available to us in an aggregate amount of up to $40.0 million , or the Revolving Loan Facility. Availability under the Revolving Loan Facility is subject to a borrowing base comprised of eligible receivables and eligible inventory as set forth in the Loan and Security Agreement. Proceeds from the revolving line of credit may be used for working capital and general business purposes. The Revolving Loan Facility is secured by substantially all of our personal property other than intellectual property. The Revolving Loan Facility restricts our ability to grant any interest in our intellectual property other than certain permitted licenses and permitted encumbrances set forth in the Revolving Loan Facility. The principal amount outstanding under the revolving line bears interest at a floating rate per annum equal to the greater of (i) 2.0% above the “prime rate,” as reported in The Wall Street Journal and (ii) 6.75% , which interest is payable monthly. Principal amounts borrowed under the revolving line of credit may be repaid and, prior to the maturity date, re-borrowed, subject to the terms and conditions set forth in the Revolving Loan Facility. The Revolving Loan Facility will mature on the date that is two years after the effective date of the Loan and Security Agreement. Upon entry into the Loan and Security Agreement (payable in installments and subject to certain conditions), and at the one year anniversary thereof, we must pay to SVB a fee equal to 1.00% of the Revolving Loan Facility. We are also required to pay on a quarterly basis a fee equal to 0.25% per annum of the average unused portion of the revolving line. We must pay a termination fee of 2.00% of the Revolving Loan Facility, if the revolving line is terminated prior to the maturity date, subject to certain exceptions.

Basis of Presentation and Sum21

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements were prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they may not include all of the information and footnotes required by GAAP for complete financial statements. All adjustments that are, in the opinion of management, of a normal recurring nature and are necessary for a fair presentation of these interim financial statements have been included. These interim condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements contained in our Annual Report on Form 10-K for the year ended December 31, 2017 . The year-end condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by GAAP. The results of operations for the three and six months ended June 30, 2018 are not necessarily indicative of the results that may be expected for the entire fiscal year or any other interim period.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include our financial statements and those of our wholly-owned subsidiaries. Intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of our condensed consolidated financial statements, which have been prepared in accordance with GAAP requires us to make estimates, judgments and assumptions that affect the reported amounts of assets, liabilities, equity revenue and expenses and related disclosure of contingent assets and liabilities. On an ongoing basis, we evaluate our estimates, judgments and assumptions. We base our estimates on historical experience, known trends and events and various other factors that we believe to be reasonable under the circumstances. These estimates are subject to an inherent degree of uncertainty, and as a result, actual results may differ from these estimates under different assumptions or conditions.
Revenue Recognition	Revenue Recognition Effective January 1, 2018, we adopted Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606) , using the modified retrospective transition method. Under this transition method, we will not revise our consolidated financial statements for the years ended December 31, 2017 and 2016, and applicable interim periods within those years. Disclosure will be provided to show the impact to the consolidated financial statements, if any, as if ASU, 2014-09 had been effective for those periods. Our primary source of revenue during the reporting periods was product sales. We sell product to a limited number of major wholesalers, or our Distributors, as well as certain pharmacies, or collectively with our Distributors, our Customers. Our Distributors resell the product to retail pharmacies for purposes of their reselling the product to fill patient prescriptions. Under the new revenue standards, we recognize product revenue when our Customer obtains control of promised goods, in an amount that reflects the consideration which we expect to receive in exchange for those goods. We recognize revenue following the five step model prescribed under ASU No. 2014-09: (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) we satisfy the performance obligation. Product Revenue: We sell product to a limited number of our Distributors as well as certain specialty pharmacies. Our Distributors resell the product to retail pharmacies for purposes of filling patient prescriptions. In addition to agreements with Customers, we enter into arrangements with health care providers and payors that provide for government-mandated or privately-negotiated discounts and rebates with respect to the purchase of our product. Revenue from product sales are recognized when the Customer obtains control of our product, which occurs at a point in time, typically upon delivery to the Customer. We expense incremental costs of obtaining a contract as and when incurred if the expected amortization period of the asset that we would have recognized is one year or less. Reserves for Discounts and Allowances: Revenue from product sales are recorded at the transaction price, which is equal to the sales price net of reserves for discounts and allowances that are offered within contracts with our Customers, health care providers, payors or other indirect customers. These discounts and allowances represent variable consideration under the new revenue standards. Our process for estimating these components of variable consideration do not differ materially from our historical practices. Product revenue reserves are classified as a reduction in product revenue and are generally characterized in the following categories: trade allowances, rebates and chargebacks, product returns and other incentives. These reserves are based on estimates of the amounts earned or to be claimed on the related sale of product and are classified as either a reduction of accounts receivable or an accrued expense (current liability) on our consolidated balance sheets, depending on whether the consideration is paid to a direct customer or another third party with which we contract (e.g. provider or payor) and the method of payment. Our estimates of reserves for variable consideration typically utilize the most likely method and reflect our historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Our product revenue reserves reflect our best estimates of the amount of consideration to which we are entitled based on the terms of the individual contracts. The transaction price, which includes variable consideration reflecting the impact of discounts and allowances, may be subject to constraint and is included in the net sales price only to the extent that it is probable that a significant reversal of the amount of the cumulative revenues recognized will not occur in a future period. Actual amounts may ultimately differ from our estimates. If actual results vary, we adjust these estimates, which could have an effect on earnings in the period of adjustment. License Revenue: Our license revenue consists of license fees, royalties and milestone payments arising from our agreement with JT and Torii. We receive royalty revenues on sales by JT and Torii of Riona in Japan. We do not have future performance obligations under this license arrangements. We record these royalty revenues based on estimates of the net sales that occurred during the relevant period as license revenue. The relevant period estimate of sales is based on analysis of historical royalties that have been paid to us, adjusted for any changes in facts and circumstances, as appropriate. Differences between actual and estimated royalty revenues are adjusted in the period in which they become known, typically the following quarter. Disaggregation of Revenue Currently, our only product is Auryxia, which we commercialize only in the United States. We have no foreign operations; however, we currently generate license revenue based on net sales of Riona by our partner in Japan, as discussed above. License revenue for all periods presented represents royalty revenue generated from our sublicense agreement with JT and Torii. Significant Judgments Our revenue reserves, consisting of various discounts and allowances, which are components of variable consideration as discussed above, are considered an area of significant judgment. Additionally, our license revenue in each period, as discussed above, is based on estimates of the net sales of our Japanese partner that occurred during the relevant period. The relevant period estimate of sales is based on analysis of historical royalties that have been paid to us, adjusted for any changes in facts and circumstances, as appropriate, and is considered an area of significant judgment. For these areas of significant judgment, actual amounts may ultimately differ from our estimates and are adjusted in the period in which they become known. Practical Expedients Significant financing component : Our accounts receivable arise from product sales and primarily represent amounts due from our wholesale and other third-party distributors. We do not adjust our receivables for the effects of a significant financing component at contract inception if we expect to collect the receivables in one year or less from the time of sale. Cost to obtain a contract : We recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that we otherwise would have recognized is one year or less or the amount is immaterial. Sales taxes : Taxes collected from Customers relating to product sales and remitted to governmental authorities, if any, are excluded from revenues.
Basic and Diluted Net Loss Per Common Share	Basic and Diluted Net Loss Per Common Share Basic net loss per share is computed by dividing the losses allocable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss per share does not reflect the effect of shares of common stock to be issued upon the exercise of stock options, as their inclusion would be anti-dilutive.
Concentrations of Credit Risk	Concentrations of Credit Risk We do not have significant off-balance sheet risk or credit risk concentrations. We maintain our cash and cash equivalents with multiple financial institutions. As of June 30, 2018 , approximately $2.0 million of our total $49.5 million cash and cash equivalents balance was invested in institutional money market funds. See Note 3 – Fair Value Measurements . Our accounts receivable, net at June 30, 2018 and December 31, 2017 represent amounts due to us from our Customers. We perform ongoing credit evaluations of our Customers and generally do not require collateral.
New Accounting Pronouncements	New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or the FASB, or other standard setting bodies that we adopt as of the specified effective date. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , a comprehensive new standard which amends revenue recognition principles and provides a single set of criteria for revenue recognition among all industries. The new standard provides a five-step framework whereby revenue is recognized when promised goods or services are transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires enhanced disclosures pertaining to revenue recognition in both interim and annual periods. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The FASB has subsequently issued amendments to ASU No. 2014-09 that have the same effective date and transition date: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations ; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing ; ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients ; and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers . We adopted these amendments with ASU 2014-09, or collectively, the new revenue standards. The new revenue standards became effective for us on January 1, 2018 and were adopted using the modified retrospective method. The adoption of the new revenue standards did not have a material impact on our revenue recognition as the majority of our revenues continue to be recognized when the Customer takes control of our product. However, the adoption of the new revenue standards did result in an adjustment to retained earnings (accumulated deficit) as of the adoption date of $0.6 million related to our license revenue and related license expense. See Note 8 – License Agreements for further discussion. Under the new revenue standards, we recognize revenues when our Customer obtains control of promised goods, in an amount that reflects the consideration which we expect to receive in exchange for those goods. We recognize revenues following the five step model prescribed under ASU No. 2014-09: (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenues when (or as) we satisfy the performance obligation. In February 2016, the FASB issued ASU No. 2016-02, Leases . The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The new standard will be effective for us on January 1, 2019 and is required to be applied using a modified retrospective transition approach with application of the new guidance for all periods presented. We are in the process of reviewing contracts with our contract manufacturers to determine whether these agreements contain any potential embedded leases. Although our assessment is not complete, we currently expect the adoption of this guidance to result in the addition of material balances of leased assets and corresponding lease liabilities to our consolidated balance sheets. We do not currently expect a material impact to our consolidated statements of operations as a result of this standard. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . The new standard addresses eight specific cash flow issues with the objective of reducing the existing diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The new standard was effective for us on January 1, 2018. The standard did not have a material impact on our consolidated statements of cash flows upon adoption.

Basis of Presentation and Sum22

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Schedule of Provisions for Allowances and Accruals	Our U.S. Auryxia product sales for the three and six months ended June 30, 2018 and 2017 were offset by provisions for allowances and accruals as set forth in the tables below. (in thousands) Three months ended Percent of gross Auryxia product sales Three months ended Percent of gross Auryxia product sales Gross Auryxia product sales $ 46,821 $ 26,029 Less provision for product sales allowances and accruals: Trade allowances 4,957 11% 2,463 9% Rebates, chargebacks and discounts 16,135 35% 8,784 34% Product returns 572 1% 346 2% Other incentives (1) 1,052 2% 320 1% Total 22,716 49% 11,913 46% Net U.S. Auryxia product sales $ 24,105 $ 14,116 (1) Includes co-pay assistance and voucher rebates. (in thousands) Six months ended June 30, 2018 Percent of gross Six months ended June 30, 2017 Percent of gross Gross Auryxia product sales $ 87,960 $ 43,983 Less provision for product sales allowances and accruals: Trade allowances 9,140 10% 4,228 9% Rebates, chargebacks and discounts 30,928 35% 14,114 32% Product returns 736 1% 278 1% Other incentives (1) 2,429 3% 742 2% Total 43,233 49% 19,362 44% Net U.S. Auryxia product sales $ 44,727 $ 24,621 (1) Includes co-pay assistance and voucher rebates.
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following table presents amounts that were excluded from the calculation of diluted net loss per share, due to their anti-dilutive effect: (in thousands) June 30, 2018 June 30, 2017 Options to purchase common stock 11,044 12,469 Shares issuable upon conversion of convertible senior notes 35,582 33,422 Shares issuable under Notes Conversion Agreement (1) 4,000 — 50,626 45,891 (1) See Note 14 - Strategic Merger with Akebia Therapeutics, Inc.
Customer Who Represented 10% Or More Total Account Receivable	The following table sets forth Customers who represented 10% or more of our total accounts receivable, net as of June 30, 2018 and December 31, 2017 . June 30, 2018 December 31, 2017 Fresenius Medical Care Rx 29 % 34 % AmerisourceBergen Drug Corporation 20 % 20 % Cardinal Health, Inc. 17 % 25 % DaVita Rx 16 % — % McKesson Corporation 14 % 17 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements of Financial Assets	The following table provides the fair value measurements of applicable financial assets as of June 30, 2018 and December 31, 2017 : Financial assets at fair value Financial assets at fair value (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets: Cash equivalents (1) $ 2,010 $ — $ — $ 1,895 $ — $ — Total assets $ 2,010 $ — $ — $ 1,895 $ — $ — (1) Cash equivalents as of June 30, 2018 and December 31, 2017 consisted of institutional money market funds. The carrying value of our money market funds approximates fair value due to their short-term maturities.

Inventory (Tables)

Inventory (Tables)	6 Months Ended
	Jun. 30, 2018
Inventory Disclosure [Abstract]
Summary of Inventories	Inventory consists of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Raw materials $ 1,493 $ 469 Work in process 43,761 25,160 Finished goods 3,330 3,066 Total inventory $ 48,584 $ 28,695

Other Assets (Tables)

Other Assets (Tables)	6 Months Ended
	Jun. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Other Current Assets	Other current assets consisted of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Prepaid manufacturing costs $ 7,121 $ 7,646 Prepaid selling, general and administrative expenses 3,616 2,265 Prepaid research and development expenses 1,405 1,288 Total other current assets $ 12,142 $ 11,199
Schedule of Other Assets, Net	Other assets, net consisted of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Deferred manufacturing costs $ 10,433 $ 7,338 Deposits 1,159 1,099 Long-term prepaid manufacturing costs 1,000 1,000 Deferred registration fees 140 140 Total other long-term assets $ 12,732 $ 9,577

Stock-Based Compensation Expe26

Stock-Based Compensation Expense (Tables)	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes stock option activity for the six months ended June 30, 2018 : Number of shares Weighted average exercise price Outstanding at December 31, 2017 11,967,815 $ 6.73 Granted 980,000 4.11 Exercised (204,521 ) 3.80 Forfeited or Expired (1,699,249 ) 5.85 Outstanding at June 30, 2018 11,044,045 $ 6.68 Vested and expected to vest at June 30, 2018 8,917,383 $ 6.93 Exercisable at June 30, 2018 5,809,968 $ 8.00
Summary of Restricted Share Activity	The following table summarizes restricted share activity for the six months ended June 30, 2018 : Number of shares Weighted average grant date fair value Outstanding at December 31, 2017 1,884,297 $ 6.39 Granted 1,523,650 4.45 Vested (598,170 ) 5.62 Forfeited (487,267 ) 4.90 Outstanding at June 30, 2018 2,322,510 $ 5.63
Stock Based Compensation Expense	The following table reflects stock-based compensation expense for the three and six months ended June 30, 2018 and 2017 : Three months ended June 30, Six months ended June 30, (in thousands) 2018 2017 2018 2017 Cost of goods sold $ 25 $ 28 $ 43 $ 88 Research and development 570 483 1,312 1,061 Selling, general and administrative 4,377 3,161 7,298 6,187 Total stock-based compensation expense $ 4,972 $ 3,672 $ 8,653 $ 7,336

Accounts Payable And Accrued 27

Accounts Payable And Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2018
Payables and Accruals [Abstract]
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consists of the following at June 30, 2018 and December 31, 2017 : (in thousands) June 30, 2018 December 31, 2017 Commercial rebates and fees $ 21,056 $ 16,362 Accounts payable 17,582 6,474 Professional, license, and other fees and expenses 9,252 5,257 Accrued compensation and related liabilities 5,994 7,504 Accrued manufacturing expenses 763 9,434 Total accounts payable and accrued expenses $ 54,647 $ 45,031

Other Income (Expense), Net (Ta

Other Income (Expense), Net (Tables)	6 Months Ended
	Jun. 30, 2018
Other Income and Expenses [Abstract]
Schedule of Other Income (Expense)	The components of other income (expense), net are as follows: Three months ended June 30, Six months ended June 30, (in thousands) 2018 2017 2018 2017 Interest income $ 179 $ 118 $ 380 $ 235 Other income (expense) (230 ) (5 ) (209 ) (8 ) Fair value adjustment to derivative liability — 225 — 225 Total other income (expense), net $ (51 ) $ 338 $ 171 $ 452

Basis of Presentation and Sum29

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Provisions for Allowances and Accruals (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for Sales Return and Doubtful Accounts [Line Items]
Gross Auryxia product sales	$ 46,821	$ 26,029	$ 87,960	$ 43,983
Provision for product sales allowances and accruals	22,716	11,913	43,233	19,362
Net U.S. Auryxia product sales	$ 24,105	$ 14,116	$ 44,727	$ 24,621
Provision for product sales allowances and accruals, percentage	49.00%	46.00%	49.00%	44.00%
Trade allowances
Allowance for Sales Return and Doubtful Accounts [Line Items]
Provision for product sales allowances and accruals	$ 4,957	$ 2,463	$ 9,140	$ 4,228
Provision for product sales allowances and accruals, percentage	11.00%	9.00%	10.00%	9.00%
Rebates, chargebacks and discounts
Allowance for Sales Return and Doubtful Accounts [Line Items]
Provision for product sales allowances and accruals	$ 16,135	$ 8,784	$ 30,928	$ 14,114
Provision for product sales allowances and accruals, percentage	35.00%	34.00%	35.00%	32.00%
Product returns
Allowance for Sales Return and Doubtful Accounts [Line Items]
Provision for product sales allowances and accruals	$ 572	$ 346	$ 736	$ 278
Provision for product sales allowances and accruals, percentage	1.00%	2.00%	1.00%	1.00%
Other Incentives
Allowance for Sales Return and Doubtful Accounts [Line Items]
Provision for product sales allowances and accruals	$ 1,052	$ 320	$ 2,429	$ 742
Provision for product sales allowances and accruals, percentage	2.00%	1.00%	3.00%	2.00%

Basis of Presentation and Sum30

Basis of Presentation and Summary of Significant Accounting Policies - Stock Excluded From Calculation (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	50,626	45,891
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	11,044	12,469
Shares issuable upon conversion of convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	35,582	33,422
Shares issuable under Notes Conversion Agreement
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Option outstanding, not included in computation of net loss per share amount (in shares)	4,000	0

Basis of Presentation and Sum31

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Money market funds	$ 2,000
Cash and cash equivalents	49,458		$ 93,526	$ 140,527	$ 111,810
Adjustment to accumulated deficit	$ 1,041,336		$ 998,538
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to accumulated deficit		$ 600

Basis of Presentation and Sum32

Basis of Presentation and Summary of Significant Accounting Policies - Customer Who Represented 10% Or More Total Account Receivable (Detail) - Accounts Receivable, net - Customer Concentration Risk	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fresenius Medical Care Rx
Concentration Risk [Line Items]
Concentration risk percentage	29.00%	34.00%
AmerisourceBergen Drug Corporation
Concentration Risk [Line Items]
Concentration risk percentage	20.00%	20.00%
Cardinal Health, Inc.
Concentration Risk [Line Items]
Concentration risk percentage	17.00%	25.00%
DaVita Rx
Concentration Risk [Line Items]
Concentration risk percentage	16.00%	0.00%
McKesson Corporation
Concentration Risk [Line Items]
Concentration risk percentage	14.00%	17.00%

Fair Value Measurements (Detail

Fair Value Measurements (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Level 1
Assets:
Total assets	$ 2,010	$ 1,895
Level 2
Assets:
Total assets	0	0
Level 3
Assets:
Total assets	0	0
Cash Equivalents | Level 1
Assets:
Total assets	2,010	1,895
Cash Equivalents | Level 2
Assets:
Total assets	0	0
Cash Equivalents | Level 3
Assets:
Total assets	$ 0	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions	Jun. 28, 2018	May 09, 2018	Oct. 31, 2015	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Proceeds from issuance of convertible senior notes				$ 10,000	$ 0
Proceeds from Issuance of Common Stock		$ 10,000		0	$ 73,125
Convertible debt, fair value disclosures				$ 133,800		$ 155,400
Additional shares issued (in shares)		2.2
Convertible Senior Notes, due 2020
Debt Instrument [Line Items]
Proceeds from issuance of convertible senior notes			$ 125,000
Convertible Debt | Convertible Senior Notes due 2021
Debt Instrument [Line Items]
Senior notes issued		$ 164,746
Additional shares issued (in shares)	4	4

Inventory - Summary of Inventor

Inventory - Summary of Inventories (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 1,493		$ 1,493		$ 469
Work in process	43,761		43,761		25,160
Finished goods	3,330		3,330		3,066
Total inventory	48,584		48,584		$ 28,695
Inventory written off	$ 1,200	$ 300	$ 5,288	$ 335

Other Assets - Schedule of Othe

Other Assets - Schedule of Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid manufacturing costs	$ 7,121	$ 7,646
Prepaid selling, general and administrative expenses	3,616	2,265
Prepaid research and development expenses	1,405	1,288
Total other current assets	$ 12,142	$ 11,199

Other Assets - Schedule of Ot37

Other Assets - Schedule of Other Assets, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred manufacturing costs	$ 10,433	$ 7,338
Deposits	1,159	1,099
Long-term prepaid manufacturing costs	1,000	1,000
Deferred registration fees	140	140
Total other long-term assets	$ 12,732	$ 9,577

Other Assets - Narrative (Detai

Other Assets - Narrative (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred costs facility construction milestone	$ 5,000,000	$ 5,000,000
Deferred cost product premiums	2,400,000	2,300,000
Deferred manufacturing included in current liabilities	$ 0	$ 7,300,000

Stockholders' Deficit - Additio

Stockholders' Deficit - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders’ deficit	$ 41,192		$ 41,192			$ 14,095
Increase in stockholders' deficit			27,100
Net loss	(21,518)	$ (86,497)	(43,414)	$ (109,513)
Proceeds related to issuance of stock-based compensation and sock option exercises			8,700
Additional debt discount			6,228	$ 0
Adjustment to accumulated deficit	$ 1,041,336		$ 1,041,336			$ 998,538
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to accumulated deficit					$ 600

Stock-Based Compensation Expe40

Stock-Based Compensation Expense - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for the issuance of stock options (in shares)	7,768,360		7,768,360
Stock awards vesting period			3 years
Stock-based compensation expense related to equity incentive granted	$ 4,972	$ 3,672	$ 8,653	$ 7,336
Weighted average grant date fair value of stock options granted (in dollars per shares)	$ 2.42	$ 4.65	$ 2.87	$ 3.86
Total unrecognized compensation cost related to non-vest stock options	$ 9,200		$ 9,200
Non-vested Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average recognition periods for unrecognized compensation cost			2 years 2 months 12 days
Non-vested Stock Options | Unvested Performance-Based Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options (in shares)	3,177,500		3,177,500
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock issued (in shares)	2,322,510		2,322,510		1,884,297
Total unrecognized compensation cost related to restricted stock	$ 8,100		$ 8,100
Weighted average recognition periods for unrecognized compensation cost			1 year 10 months 12 days
Restricted Stock | Performance-based and vest upon achievement of certain corporate milestones
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock issued (in shares)	310,000		310,000

Stock-Based Compensation Expe41

Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) - Un-vested, Performance-Based Options	6 Months Ended
	Jun. 30, 2018$ / sharesshares
Number of shares
Outstanding at beginning of period (in shares) | shares	11,967,815
Granted (in shares) | shares	980,000
Exercised (in shares) | shares	(204,521)
Forfeited or Expired (in shares) | shares	(1,699,249)
Outstanding at end of period (in shares) | shares	11,044,045
Vested and expected to vest at period end (in shares) | shares	8,917,383
Exercisable at period end (in shares) | shares	5,809,968
Weighted-average exercise price
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 6.73
Granted (in dollars per share) | $ / shares	4.11
Exercised (in dollars per share) | $ / shares	3.80
Forfeited and Expired (in dollars per share) | $ / shares	5.85
Outstanding at end of period (in dollars per share) | $ / shares	6.68
Vested and expected to vest at period end (in dollars per share) | $ / shares	6.93
Exercisable at period end (in dollars per share) | $ / shares	$ 8

Stock-Based Compensation Expe42

Stock-Based Compensation Expense - Summary of Restricted Share Activity (Detail) - Restricted Stock	6 Months Ended
	Jun. 30, 2018$ / sharesshares
Number of shares
Outstanding at beginning of period (in shares) | shares	1,884,297
Granted (in shares) | shares	1,523,650
Vested (in shares) | shares	(598,170)
Forfeited (in shares) | shares	(487,267)
Outstanding at end of period (in shares) | shares	2,322,510
Weighted average grant date fair value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 6.39
Granted (in dollars per share) | $ / shares	4.45
Vested (in dollars per share) | $ / shares	5.62
Forfeited (in dollars per share) | $ / shares	4.90
Outstanding at end of period (in dollars per share) | $ / shares	$ 5.63

Stock-Based Compensation Expe43

Stock-Based Compensation Expense - Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,972	$ 3,672	$ 8,653	$ 7,336
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	25	28	43	88
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	570	483	1,312	1,061
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,377	$ 3,161	$ 7,298	$ 6,187

License Agreements - Additional

License Agreements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		152 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revised agreement potential milestone receivable			$ 55,000
Adjustment to accumulated deficit	$ 1,041,336		1,041,336		$ 1,041,336		$ 998,538
License revenue	1,644	$ 1,028	2,773	$ 2,343
License expense	$ 987	$ 617	$ 1,664	$ 1,406
Licensing Agreements
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments to acquire right for development and marketing of Ferric Citrate					$ 11,600
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Adjustment to accumulated deficit						$ 600

Accounts Payable And Accrued 45

Accounts Payable And Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Commercial rebates and fees	$ 21,056	$ 16,362
Accounts payable	17,582	6,474
Professional, license, and other fees and expenses	9,252	5,257
Accrued compensation and related liabilities	5,994	7,504
Accrued manufacturing expenses	763	9,434
Total accounts payable and accrued expenses	$ 54,647	$ 45,031

Debt - Additional Information (

Debt - Additional Information (Detail)	Jun. 28, 2018shares	May 09, 2018USD ($)appointmentshares$ / shares	Oct. 14, 2015$ / shares	Oct. 31, 2015USD ($)	Jun. 30, 2018USD ($)shares	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)shares	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)shares	Jun. 08, 2017shares
Debt Conversion [Line Items]
Proceeds from issuance of convertible senior notes							$ 10,000,000	$ 0
Common stock, shares authorized (in shares) | shares					230,000,000		230,000,000		230,000,000	230,000,000
Proceeds from issuance of common stock, net of commission		$ 10,000,000					$ 0	73,125,000
Stock issued during period, shares, new issues | shares		2,200,000
Interest expense					$ 1,300,000	$ 1,300,000	63,000,000	$ 63,000,000
Notes, carrying amount					130,088,000		130,088,000		$ 125,000,000
Notes, fair value					$ 133,800,000		$ 133,800,000		$ 155,400,000
Convertible Senior Notes, due 2020
Debt Conversion [Line Items]
Proceeds from issuance of convertible senior notes				$ 125,000,000
Minimum aggregate principal amount outstanding for declaration notice					25.00%		25.00%
Conversion ratio			0.2673797
Conversion price, per share (in dollars per share) | $ / shares			$ 3.74
Repurchase price percentage of the principal amount							100.00%
Convertible Senior Notes, due 2020 | Default (other than certain events of bankruptcy, insolvency or reorganization)
Debt Conversion [Line Items]
Redemption percentage							100.00%
Convertible Senior Notes, due 2020 | Events of bankruptcy, insolvency or reorganization
Debt Conversion [Line Items]
Redemption percentage							100.00%
Convertible Senior Notes due 2021
Debt Conversion [Line Items]
Conversion ratio		0.215983
Asset-backed Credit Facility
Debt Conversion [Line Items]
Line of credit facility, maximum borrowing capacity		$ 40,000,000
Convertible Debt | Convertible Senior Notes due 2021
Debt Conversion [Line Items]
Conversion price, per share (in dollars per share) | $ / shares		$ 4.63
Senior notes issued		$ 164,746,000
Shares, outstanding (in shares) | shares		33,400,000
Stock issued during period, shares, new issues | shares	4,000,000	4,000,000
Debt discount					$ 36,000,000		$ 36,000,000
Baupost
Debt Conversion [Line Items]
Number of allowable board of director appointments | appointment		1
Ownership percentage, board of directors appointment threshold		20.00%
Ownership percentage, board of directors observer appointment threshold		10.00%

Income Taxes (Details)

Income Taxes (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Income Tax Disclosure [Abstract]
Reduction to deferred tax liability as result of the Tax Cuts and Jobs Act	$ 0.6
Income tax benefit as result of the Tax Cuts and Jobs Act	$ 0.6

Other Income (Expense), Net - C

Other Income (Expense), Net - Components of Other Income (Expense), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 179	$ 118	$ 380	$ 235
Other income (expense)	(230)	(5)	(209)	(8)
Fair value adjustment to derivative liability	0	225	0	225
Total other income (expense), net	$ (51)	$ 338	$ 171	$ 452

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Detail) - Pending Litigation - lawsuit	Dec. 16, 2016	Jun. 30, 2018
Loss Contingencies [Line Items]
Loss contingency, number of class action lawsuits		4
Filed US District Court, S. District New York
Loss Contingencies [Line Items]
Loss contingency, number of class action lawsuits		3
Breach of Fiduciary Duties
Loss Contingencies [Line Items]
New claims filed	2

Strategic Merger with Akebia 50

Strategic Merger with Akebia Therapeutics, Inc. - Narrative (Details) $ / shares in Units, shares in Millions	Jun. 28, 2018USD ($)$ / sharesshares	May 09, 2018shares	Jun. 30, 2018$ / shares	Dec. 31, 2017$ / shares
Business Acquisition [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.001	$ 0.001
Additional shares issued (in shares)		2.2
Keryx Biopharmaceuticals
Business Acquisition [Line Items]
Contingent termination fee | $	$ 22,000,000
Akebia Therapeutics | Keryx Biopharmaceuticals
Business Acquisition [Line Items]
Conversion rate of acquiree stock	0.37433
Common stock, par value (in dollars per share) | $ / shares	$ 0.00001
Voting rights percentage	50.00%
Contingent termination fee | $	$ 22,000,000
Convertible Debt | Convertible Senior Notes due 2021
Business Acquisition [Line Items]
Additional shares issued (in shares)	4	4
Shares issued in conversion of debt (in shares)		35.6

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events - Narrative (Details) - Revolving Credit Facility - Line of Credit - Subsequent Event	Jul. 18, 2018USD ($)
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity	$ 40,000,000
Greater of variable or stated interest rate (stated interest rate)	6.75%
Line of credit term	2 years
Annual fee, percentage of outstanding balance	1.00%
Commitment fee percentage	0.25%
Termination fee percentage	2.00%
Prime Rate
Subsequent Event [Line Items]
Greater of variable or stated interest rate (variable interest rate)	2.00%