Relypsa (RLYP) 10-Q 7 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	1-May-15
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	RLYP
Entity Registrant Name	Relypsa Inc
Entity Central Index Key	1416792
Current Fiscal Year End Date	-19
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		41,464,385

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$82,771	$30,264
Short-term investments	239,550	105,493
Restricted cash	268	268
Other receivables	1,297	425
Prepaid expenses and other current assets	2,232	2,756
Total current assets	326,118	139,206
Long-term investments	2,006
Restricted cash	686	686
Property and equipment, net	4,893	3,467
Other assets	9,923	8,480
Total assets	343,626	151,839
Current liabilities:
Accounts payable	4,886	3,156
Accrued payroll and related expenses	2,771	4,393
Accrued liabilities	10,245	7,778
Deferred rent, current portion	64	1,156
Line of credit, current portion	438	432
Capital loan, current portion	1,379
Total current liabilities	19,783	16,915
Long-term liabilities:
Deferred rent, long-term	1,720	983
Line of credit	167	267
Capital loan	14,015	15,213
Total liabilities	35,685	33,378
Commitments and contingencies
Stockholders’ equity:
Preferred stock: $0.001 par value; 5,000 shares authorized at March 31, 2015 and December 2014; no shares issued and outstanding at March 31, 2015 and December 31, 2014
Common stock: $0.001 par value; 300,000 shares authorized at March 31, 2015 and December 31, 2014; 41,432 and 35,045 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	41	35
Additional paid-in capital	643,289	424,175
Accumulated other comprehensive income (loss)	4	-21
Accumulated deficit	-335,393	-305,728
Total stockholders’ equity	307,941	118,461
Total liabilities and stockholders’ equity	$343,626	$151,839

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	41,432,000	35,045,000
Common stock, shares outstanding	41,432,000	35,045,000

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations (Unaudited) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating expenses:
Research and development	$15,780	$10,909
General and administrative	13,487	4,795
Total operating expenses	29,267	15,704
Loss from operations	-29,267	-15,704
Interest and other income (expense), net	84	27
Interest expense	-482	-391
Net loss	($29,665)	($16,068)
Net loss per share, basic and diluted	($0.78)	($0.54)
Weighted average common shares used to compute net loss per share, basic and diluted	37,829,239	29,710,415

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	($29,665)	($16,068)
Other comprehensive loss:
Unrealized gain on available-for-sale securities, net of tax	25	4
Total comprehensive loss	($29,640)	($16,064)

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net loss	($29,665)	($16,068)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,897	263
Stock-based compensation	3,626	1,998
Amortization of debt issuance costs	10	9
Amortization of debt discount	37	37
Accretion of final debt payment	149	95
Investment premium amortization		148
Loss on disposal of fixed assets	13
Changes in assets and liabilities:
Other receivables	-872	-620
Prepaid expenses and other current assets	521	332
Other assets and restricted cash	-1,443	-234
Accounts payable	1,540	-690
Accrued and other liabilities	845	-209
Deferred rent	-355	446
Net cash used in operating activities	-23,697	-14,493
Investing activities
Purchases of investments	-175,883	-52,963
Proceeds from maturities of short-term investments	39,620
Purchases of property and equipment	-2,921	-350
Net cash used in investing activities	-139,184	-53,313
Financing activities
Net proceeds from public offerings	213,711
Proceeds from common stock option exercise	1,395
Proceeds from purchases under the Employee Stock Purchase Plan	388
Net proceeds from warrant exercise		5
Net proceeds from equipment line of credit		-760
Repayment of equipment line of credit	-106	-100
Net cash provided by (used in) financing activities	215,388	-855
Net increase (decrease) in cash and cash equivalents	52,507	-68,661
Cash and cash equivalents at beginning of period	30,264	94,759
Cash and cash equivalents at end of period	82,771	26,098
Noncash investing and financing activities
Change in unrealized gain on investments	25	4
Accounts payable related to purchase of property and equipment	$190	$467

Description_of_Business_and_Si

Description of Business and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Description of Business and Significant Accounting Policies	1.  Description of Business and Significant Accounting Policies
	Organization
	Relypsa, Inc. (Relypsa or the Company) is a biopharmaceutical company dedicated to the development and commercialization of new non-absorbed polymeric drugs for important applications in renal, cardiovascular and metabolic disease. Relypsa’s lead product candidate is Patiromer for Oral Suspension, or Patiromer FOS. A new drug application has been filed with the U.S. Food and Drug Administration (FDA) for Patiromer FOS for the treatment of hyperkalemia and is currently under review. The FDA has assigned a Prescription Drug User Fee Act, or PDUFA, action date of October 21, 2015 for completion of review for the Company’s New Drug Application (NDA). The Company commenced operations on October 29, 2007. The Company’s principal operations are based in Redwood City, California and it operates in one segment. On October 28, 2014, Relypsa UK LTD was incorporated as a wholly-owned subsidiary of the Company.
	The information included in this quarterly report on Form 10-Q should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 filed with the U.S. Securities Exchange Commission (SEC).
	Offerings
	On December 4, 2014, the Company filed a shelf registration statement on Form S-3, which permitted: (a) the offering, issuance and sale by the Company of up to a maximum aggregate offering price of $250.0 million of its common stock, preferred stock, debt securities, warrants, purchase contracts and/or units; and (b) as part of the $250.0 million, the offering, issuance and sale by the Company of up to a maximum aggregate offering price of $70.0 million of its common stock that may be issued and sold under a sales agreement with Cantor Fitzgerald & Co in one or more at-the-market offerings. As of December 31, 2014, the Company had sold 514,710 shares pursuant to its at-the-market program at an average price of $32.17 for aggregate offering proceeds of $16.6 million and the Company received aggregate net proceeds of $16.1 million.
	During January and February 2015, the Company sold 1,549,910 shares pursuant to the Company’s at-the-market program at an average price of $34.48 for aggregate offering proceeds of $53.4 million, and the Company received aggregate net proceeds of $51.8 million.  During the first quarter of 2015, the Company exhausted its current at-the-market offering in full.
	On March 3, 2015, the Company completed an underwritten public offering of 4,485,000 shares of common stock at an offering price of $38.50 per share for gross proceeds of $172.7 million. The Company received net proceeds from the offering of $161.9 million, after deducting the underwriting discounts and expenses.
	Basis of Presentation
	There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2015 as compared to the significant accounting policies described in the Company’s audited consolidated financial statements included in the Company’s Annual Report on Form 10-K filed with the SEC for the year ended December 31, 2014.
	The accompanying financial information for the three months ended March 31, 2015 is unaudited. These unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP and applicable rules and regulations of the SEC regarding interim financial reporting. Certain information and note disclosures normally included in the consolidated financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014, and include all adjustments, which include only normal recurring adjustments. Intercompany transactions and balances have been eliminated in consolidation. The results for the three months ended March 31, 2015 are not necessarily indicative of the results expected for the full fiscal year or any other period(s).
	Use of Estimates
	The preparation of these unaudited interim condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and judgments that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, manufacturing accruals, fair value of assets and liabilities, common stock, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
	Recent Accounting Pronouncements
	In April 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-03, Simplifying the Presentation of Debt Issuance Costs. The update changes the presentation of debt issuance costs in financial statements. ASU 2015-03 requires an entity to present such costs in the balance sheet as a direct deduction from the related debt liability rather than an asset. Amortization of the costs will continue to be reported as interest expense. It is effective for annual reporting periods beginning after December 15, 2016. Implementation of this update will not have a material impact on the Company's consolidated financial statements.
	Liquidity
	The Company has never been profitable and, as of March 31, 2015, the Company has an accumulated deficit of $335.4 million. The Company may continue to incur substantial operating losses even after it begins to generate meaningful revenues from Patiromer FOS, if approved. The Company will need additional funding to support future operating activities and adequate funding may not be available to the Company on acceptable terms, or at all. The Company’s failure to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition. The Company will need to generate significant revenues to achieve profitability and it may never do so.
	Research and Development Expenses
	Research and development costs are charged to expense as incurred and consist of costs incurred to further the Company’s research and development activities including salaries and related employee benefits, costs associated with clinical trials, costs related to pre-commercialization manufacturing activities such as manufacturing process validation activities and the manufacturing of commercial supply prior to approval, nonclinical research and development activities, regulatory activities, research-related overhead expenses and fees paid to external service providers and contract research and manufacturing organizations that conduct certain research and development activities on behalf of the Company.
	Net Loss per Common Share
	Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per common share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period using the treasury stock method.
	The following outstanding shares of common stock equivalents were excluded from the computations of diluted net loss per common share attributable to common stockholders for the periods presented as the effect of including such securities would be antidilutive (in thousands):
		March, 31
		2015		2014
	Warrants to purchase common stock		15		64
	Options to purchase common stock		3,731		3,610
	Restricted stock units		122		5
	Common stock subject to repurchase		1		4
			3,869		3,683

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	2.  Fair Value Measurements
	Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value should maximize the use of observable inputs and minimize the use of unobservable inputs. There is a three-level valuation hierarchy for disclosure of fair value measurements, as follows:
	Level 1 – Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.
	Level 2 – Inputs (other than quoted market prices included in Level 1) that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life.
	Level 3 – Unobservable inputs that are supported by little or no market activity and reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model.
	A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement.
	The following tables set forth the fair value of the Company’s financial instruments that were measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 (in thousands):
		Level 1			Level 2		Level 3		Total
	31-Mar-15
	Financial assets:
	Money market funds	$	15,648		$	—	$	—	$	15,648
	Corporate bonds		—			146,683		—		146,683
	Agency bonds		—			61,538		—		61,538
	Commercial paper		—			96,801		—		96,801
	Total financial assets	$	15,648		$	305,022	$	—	$	320,670
	Liabilities:
	Contingent put option liability	$	—		$	—	$	233	$	233
	Total liabilities	$	—		$	—	$	233	$	233
		Level 1			Level 2		Level 3		Total
	31-Dec-14
	Financial assets:
	Money market funds	$	10,202		$	—	$	—	$	10,202
	Corporate bonds		—			71,763		—		71,763
	Agency bonds		—			15,162		—		15,162
	Commercial paper		—			30,846		—		30,846
	Total financial assets	$	10,202		$	117,771	$	—	$	127,973
	Liabilities:
	Contingent put option liability	$	—		$	—	$	233	$	233
	Total liabilities	$	—		$	—	$	233	$	233
	As of March 31, 2015, the Company’s Level 3 liability is comprised of a contingent put option liability. The following table sets forth a summary of the changes in the estimated fair value of the Company’s contingent put option, which are measured at fair value on a recurring basis (in thousands):
	Balance as of December 31, 2014		$	233
	Decrease in fair value included in other income (expense)			—
	Balance as of March 31, 2015		$	233
	Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds as Level 1. When quoted market prices are not available for the specific security, then the Company estimates fair value by using benchmark yields, reported trades, broker/dealer quotes, and issuer spreads; these securities are classified as Level 2. The Company classifies corporate bonds, commercial paper, agency bonds and certificates of deposit as Level 2. In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3. The Company classified a contingent put option liability as a Level 3 liability. See Note 4 “Borrowings,” for further description. The fair value of the contingent put option liability was determined by using a risk-neutral valuation model, wherein the fair value of the underlying debt facility is estimated both with and without the presence of the default provisions, holding all other assumptions constant. The resulting difference between the two estimated fair values is the estimated fair value of the default provisions, or the contingent put option. The fair value of the underlying debt facility is estimated by calculating the expected cash flows in consideration of an estimated probability of default and expected recovery rate in default, and discounting such cash flows back to the reporting date using a risk-free rate. The carrying value of the underlying debt facility or capital loan approximates fair value. Changes to the estimated fair value of the contingent put option will be recorded in interest and other income (expense), net in the condensed consolidated statement of operations.
	The carrying values of the Company’s financial instruments, such as cash equivalents, other receivables, accounts payable, accrued liabilities and line of credit approximate fair value due to the short-term nature of these items.
	There were no transfers between Level 1, Level 2, and Level 3 during the periods presented.

Cash_Cash_Equivalents_and_Inve

Cash, Cash Equivalents, and Investments	3 Months Ended
	Mar. 31, 2015
Cash And Cash Equivalents [Abstract]
Cash,Cash Equivalents, and Investments	3.  Cash, Cash Equivalents, and Investments
	The following is a summary of cash, cash equivalents, and investments (in thousands):
		Amortized		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair
				Gains		Losses			Value
	31-Mar-15
	Cash and money market funds	$	19,305	$	—	$	—		$	19,305
	Corporate bonds		146,709		10		(36	)		146,683
	Agency bonds		61,541		3		(6	)		61,538
	Commercial paper		96,768		33		—			96,801
	Total financial assets	$	324,323	$	46	$	(42	)	$	324,327
	Reported as:
	Cash and cash equivalents								$	82,771
	Investments									241,556
									$	324,327
		Amortized		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair
				Gains		Losses			Value
	31-Dec-14
	Cash and money market funds	$	17,986	$	—	$	—		$	17,986
	Corporate bonds		71,794		2		(33	)		71,763
	Agency bonds		15,163		2		(3	)		15,162
	Commercial paper		30,835		11		—			30,846
	Total financial assets	$	135,778	$	15	$	(36	)	$	135,757
	Reported as:
	Cash and cash equivalents								$	30,264
	Investments									105,493
									$	135,757
	For the three months ended March 31, 2015 and the year ended December 31, 2014, there were no realized gains or losses on the available-for-sale securities. As of March 31, 2015, the Company had available-for-sale securities classified as short-term investments of $239.6 million and available-for-sale securities classified as long-term investments of $2.0 million.
	All of the Company’s available-for-sale securities are subject to a periodic impairment review. The Company considers a debt security to be impaired when its fair value is less than its carrying cost, in which case the Company would further review the investment to determine whether it is other-than-temporarily impaired. When the Company evaluates an investment for other-than-temporary impairment, the Company reviews factors such as the length of time and extent to which fair value has been below cost basis, the financial condition of the issuer and any changes thereto, intent to sell, and whether it is more likely than not the Company will be required to sell the investment before the recovery of its cost basis. If an investment is other-than-temporarily impaired, the Company writes it down through earnings to its impaired value and establishes that as a new cost basis for the investment. The Company did not identify any of its available-for-sale securities as other-than-temporarily impaired in any of the periods presented. As of March 31, 2015, no investment was in a continuous unrealized loss position for more than one year, the unrealized losses were not due to change in credit risk and the Company believes that is more likely than not the investments will be held until maturity or a forecasted recovery of fair value.

Borrowings

Borrowings	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Borrowings	4.  Borrowings
	Capital Loan
	On May 30, 2014, the Company entered into an Amended and Restated Loan and Security Agreement (the Amended Loan Agreement) with Oxford Finance LLC and Silicon Valley Bank to amend and restate in its entirety the Loan and Security Agreement, (the Original Agreement), dated January 31, 2013. Per the terms of the Amended Loan Agreement, upon closing, the Company immediately drew $15.0 million, of which approximately $11.0 million was used to repay the outstanding debt under the Original Agreement, and approximately $0.4 million was used to satisfy the accrued portion of the final payment fee under the Original Agreement. Payments on the new $15.0 million loan will be interest only through January 2016, followed by 30 months of equal monthly payments of interest and principal. Due to the acceptance of the Company’s New Drug Application for Patiromer FOS by the U.S. Food and Drug Administration in December 2014, the interest only payment period was extended until January 2016 and the Company may, at its option, draw an additional $20.0 million between July 1, 2015 and December 31, 2015. The Company will be required to make a final payment upon loan maturity of 8.5% of the amounts advanced and the unaccrued portion of the final payment fee under the Original Agreement in the amount of approximately $0.4 million. The interest rate for the first tranche is 7.40% and the interest rate on the second tranche will be equal to the greater of (i) the three month LIBOR rate plus 7.17% or (ii) 7.40%.
	On January 31, 2013, the Company issued warrants to purchase 54,437 shares of Series C-1 convertible preferred stock at an exercise price of $9.1848 in connection with the Original Agreement. Upon the Company’s IPO in November 2013, the warrants to purchase convertible preferred stock were converted to warrants to purchase common stock. 13,609 of these warrants were exercised during 2014, resulting in the net issuance of 7,808 shares of common stock.  The remaining 40,828 warrants were exercised in the three months ended March 31, 2015, resulting in the net issuance of 29,690 shares of common stock.
	On May 30, 2014, the Company issued warrants to purchase 12,661 shares of common stock at an exercise price of $23.69 in connection with the first $15.0 million tranche under the Amended Loan Agreement. The fair value of the warrants was $0.2 million at the issuance date and was estimated using the Black-Scholes model with the following assumptions: a risk-free interest rate of 2.06%, a life of 7 years, a volatility factor of 91.67%, and no dividend yield. This amount is recorded as a debt discount, which will be amortized into interest expense over the repayment period. Interest expense was $0.5 million and $0.4 million for the three months ended March 31, 2015 and 2014.
	Upon an event of default, Oxford Finance LLC and Silicon Valley Bank have the option to accelerate repayment of the Amended Loan Agreement, including payment of any applicable prepayment charges, which range from 1%-3% of the outstanding loan balance and accrued interest, as well as a final payment fee. This option is considered a contingent put option liability, as the holder of the loan may exercise the option in the event of default, and is considered an embedded derivative, which must be valued and separately accounted for in the Company’s consolidated financial statements. As of March 31, 2015 the estimated fair value of the contingent put option liability was $0.2 million, which was determined by using a risk-neutral valuation model, see Note 2 for details on fair value measurement of the option.
	The Amended Loan Agreement includes customary operating but non-financial covenants, including limitations on the Company’s ability to incur additional indebtedness, issue dividends and transfer or encumber any collateral securing the debt, as well as a cross-default provision with regard to the Company’s equipment line of credit. As of March 31, 2015, principal of $15.0 million was outstanding under the Amended Loan Agreement, and the Company was in compliance with all required covenants.
	Line of Credit
	In May 2013, the Company entered into a $1.6 million equipment line of credit with a bank. The terms of repayment are 36 monthly payments, and the interest rate is fixed at 5.75%. The Company will be required to make a final payment of 9.25% of the amounts advanced. The outstanding balance on the credit line is secured by a first priority lien over all equipment purchased using the line of credit. In connection with the Company’s equipment line of credit, the Company issued a warrant to purchase 6,968 shares of Series C-1 convertible preferred stock. Upon the Company’s IPO in November 2013, the warrants to purchase convertible preferred stock were converted to warrants to purchase common stock.
	The fair value of the warrants of $25,000 at the issuance date was estimated using the Black-Scholes model with the following assumptions: a risk-free interest rate of 1.07%, a life of 7 years, a volatility factor of 91.6%, and no dividend yield. This amount is recorded as a debt discount, which is being amortized into interest expense over the repayment period. Interest expense was approximately $21,000 and $46,000 for the three months ended March 31, 2015 and 2014. These warrants were exercised during 2014, resulting in the net issuance of 3,998 shares of common stock.
	The equipment line of credit includes customary operating but non-financial covenants, including limitations on the Company’s ability to incur additional indebtedness, issue dividends and transfer or encumber any collateral securing the debt, as well as a cross-default provision with regard to the Company’s term loan. The Company utilized $1.3 million of the line of credit in the second quarter of 2013, and the remaining $0.3 million balance available under the line of credit expired unused on June 30, 2013. As of March 31, 2015, principal of $0.5 million was outstanding under the line of credit, and the Company was in compliance with all required covenants.

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5.  Commitments and Contingencies
	Lanxess Corporation
	On January 9, 2014, the Company entered into a Manufacturing and Supply Agreement (the Lanxess Supply Agreement) with Lanxess that supersedes an earlier agreement, the Memorandum of Understanding that was executed on November 27, 2012. Under the Supply Agreement, Lanxess has agreed to manufacture and supply for commercial sale the active pharmaceutical ingredient (API) for Patiromer FOS. The Lanxess Supply Agreement terminates on December 31, 2020 unless terminated earlier. The Company may extend the Lanxess Supply Agreement for an additional five years with notice. The Lanxess Supply Agreement may be terminated (i) by the Company with notice if it abandons development or manufacturing of Patiromer FOS or fails to obtain FDA approval or the parties disagree regarding the feasibility or price of certain specification changes, or with notice at least 24 months in advance, which may be given after October 1, 2015, (ii) by Lanxess with notice if the Company fails to issue certain purchase orders, or with notice at least 24 months in advance, which may be given after October 1, 2015 and (iii) by either party with notice in the event of certain delays by the other party in performing its material obligations, or with notice if the parties fail to timely agree on certain price terms beginning in September 2015. Under the Lanxess Supply Agreement, Lanxess is obligated to manufacture the Company’s commercial supply of API for Patiromer FOS, and the Company is obligated to purchase from Lanxess such products manufactured, pursuant to the terms and conditions of the Lanxess Supply Agreement.
	During 2013 and 2014, the Company paid Lanxess for plant modifications that are required to support the manufacturing scale up of API for Patiromer FOS in anticipation of commercial launch. These payments are recorded in other assets and are being amortized to research and development expenses in accordance with the period over which the Company expects to derive future economic value. Upon receiving FDA approval, the amortization cost will no longer be recognized as a research and development cost expense, but as part of the cost basis of inventory. Lanxess will have full ownership of the purchased equipment and may manufacture other products with the modified plant when not occupied by production of the API for Patiromer FOS.
	DPx Fine Chemicals
	On May 14, 2014, the Company entered into a Manufacturing and Supply Agreement (the DPx Supply Agreement) with DPx Fine Chemicals Austria GmbH & Co KG (DPx Fine Chemicals), formally DSM Fine Chemicals Austria NFG GMBH & Co. KG. Under the DPx Supply Agreement, DPx Fine Chemicals has agreed to manufacture and supply for commercial sale the API for Patiromer FOS. Under the DPx Supply Agreement, the Company is obligated to make certain minimum purchases of API. The DPx Supply Agreement may be terminated (i) by the Company with notice if it abandons development or commercialization of Patiromer FOS or fails to obtain FDA approval, or with 12 months’ notice and without cause after DPx Fine Chemicals’ manufacture and release of certain quantity of API; (ii) by DPx Fine Chemicals within 24 months’ notice and without cause after its manufacture and release of a certain quantity of API; and (iii) by either party with notice for the other party’s uncured material breach, insolvency, liquidation, bankruptcy or dissolution.
	DPx Fine Chemicals has agreed to make plant modifications under the DPx Supply Agreement and will be the exclusive owner of the purchased equipment. DPx Fine Chemicals may manufacture other products with the modified plant when not occupied by the API for Patiromer FOS. Under the DPx Supply Agreement, the Company has agreed to reimburse DPx Fine Chemicals up to a specified amount for plant modifications. These payments will be recorded in other assets and upon being placed into service, these payments will be amortized to research and development expenses in accordance with the period over which the Company expects to derive future economic value. Upon receiving FDA approval, the amortization cost will no longer be recognized as a research and development cost expense, but as part of the cost basis of inventory. DPx Fine Chemicals will have full ownership of the purchased equipment and may manufacture other products with the modified plant.
	Patheon
	On September 5, 2014, the Company entered into a multi-year supply agreement (the Patheon Supply Agreement) with Patheon, Inc. (Patheon). Under the Patheon Supply Agreement, Patheon has agreed to manufacture and supply for commercial sale the bulk and finished drug product, referred to as Patiromer FOS. The Company has agreed to supply API for Patiromer FOS to Patheon for use in the manufacture and supply of the bulk and finished drug product, and has agreed, subject to certain conditions, to purchase certain quantities of bulk and finished drug product from Patheon. The Patheon Supply Agreement may be terminated by the Company with written notice under certain provisions.
	Patheon has agreed to make facility improvements under the Patheon Supply Agreement and will be the exclusive owner of the purchased equipment and facility improvements. Patheon may manufacture other products with the facility improvements when not occupied by manufacturing Patiromer FOS. Under the Patheon Supply Agreement, the Company has agreed to reimburse Patheon up to a specified amount for plant modifications. These payments are recorded in other assets and upon being placed in service, these payments will be amortized to research and development expenses in accordance with the period over which the Company expects to derive future economic value.  Upon receiving FDA approval, the amortization cost will no longer be recognized as a research and development cost expense, but as part of the cost basis of inventory.
	The following are the combined future minimum payments under the terms of the Lanxess Supply Agreement, the DPx Supply Agreement, and the Patheon Supply Agreement as of March 31, 2015.  These amounts are based on forecasts that include estimates of future market demand, quantity discounts and manufacturing efficiencies (in thousands):
	2015	$	41,756
	2016		46,900
	2017		37,800
	2018		42,400
	2019		42,201
	Thereafter		22,000
	Total future minimum payments	$	233,057
	Operating Lease
	On June 26, 2014, the Company entered into a new lease (the Lease) for office and laboratory facilities in Redwood City, California that serves as the Company’s principal executive offices.
	The Lease commenced on February 1, 2015, following the landlord’s construction of certain improvements to the premises required under the Lease.  The Lease terminates 10 years after commencement and the Company has an option to extend the Lease for an additional five years upon written notice to landlord.
	The Lease contains rent escalation provisions over the term of the Lease. In accordance with the terms of the Lease the Company provided a security deposit in the form of a $0.7 million irrevocable letter of credit that is collateralized by a $0.7 million restricted deposit at the Company’s bank. The total rent obligation will be expensed ratably over the term of the Lease.
	Future minimum operating lease payments at March 31, 2015 are as follows (in thousands):
	2015	$	1,805
	2016		3,209
	2017		3,373
	2018		3,449
	2019		3,544
	Thereafter		20,064
	Total future minimum payments	$	35,444
	The Company utilized a one-time allowance of approximately $0.6 million for costs related to relocation, cabling, furniture, fixtures and equipment. The Company is also entitled, at its election, to an additional allowance of approximately $2.2 million for certain move and tenant improvement related costs incurred by the Company prior to the second anniversary of the Lease commencement. In the event the Company elects to use all or any portion of the additional allowance, the base rent will increase.

Equity_Compensation_Plans_and_

Equity Compensation Plans and Stock Based Compensation	3 Months Ended
	Mar. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Compensation Plans and Stock Based Compensation	6.  Equity Compensation Plans and Stock Based Compensation
	The Company adopted the 2007 Equity Incentive Plan (the 2007 Plan) which provides for the granting of stock options to employees, directors and consultants of the Company. Options granted under the 2007 Plan may be either incentive stock options or nonqualified stock options. Incentive stock options may be granted only to Company employees. Nonqualified stock options may be granted to Company employees, outside directors and consultants. Options under the 2007 Plan may be granted for periods of up to ten years and are exercisable immediately, subject to rights of repurchase by the Company, which lapse over the period the applicable shares vest. Employee options granted by the Company generally vest over four years.
	In November 2013, the Company’s stockholders approved the 2013 Equity Incentive Plan (the 2013 Plan). Options granted under the 2013 Plan may be granted for periods of up to ten years and are generally exercisable when vested. Any remaining shares available for future issuance under the 2007 Stock Plan are available for issuance under the 2013 Plan.  The 2013 plan reserve will automatically increase annually from January 1, 2014 through January 1, 2023 by an amount equal to the smaller of: (a) 2,553,174 shares, (b) four percent of the number of shares of common stock issued and outstanding on the immediately preceding December 31, or (c) an amount determined by the Company's board of directors. As of March 31, 2015, a total of 1,963,355 shares were authorized for grant under the 2013 Plan. In June 2014, the Company’s board of directors approved the 2014 Employment Commencement Incentive Plan (the Inducement Plan), under which 1,000,000 shares were reserved. As of March 31, 2015, 614,600 shares of the Company’s common stock were subject to inducement grants that were issued pursuant to the Inducement Plan. The awards were made pursuant to the NASDAQ inducement grant exception as a component of the Company’s new hires’ employment compensation.
	The Company adopted the ESPP on November 2013 and in August 2014, the ESPP was initiated. As of March 31, 2015, the Company has reserved 587,438 shares of common stock for issuance under the ESPP, which permits eligible employees to purchase common stock at a discount through payroll deductions. The ESPP is a compensatory plan as defined by the authoritative guidance for stock compensation. As such stock-based compensation expense has been recorded during the three months ended March 31, 2015.
	The following table summarizes option activity under the 2007 Plan, the 2013 Plan, the Inducement Plan, and related information (in thousands, except per share and contractual term amounts):
		Shares			Shares Subject		Weighted-		Weighted-		Aggregate
		Available			to Outstanding		Average		Average		Intrinsic
		for			Options		Exercise Price		Remaining		Value
		Grant					Per Share		Contractual
									Term
									(in years)
	Options Outstanding at December 31, 2014		1,167			3,813	$	11.05
	Additional shares reserved under plan		1,402			—		—
	Options granted		(263	)		263		33.34
	Options exercised		—			-304		4.59
	Options forfeited		41			-41		22.4
	Restricted Stock Units canceled		1			—		—
	Balances at March 31, 2015		2,348			3,731	$	13.02		8.3	$	86,287
	Vested and expected to vest at March 31, 2015					3,579	$	12.72		8.2	$	83,850
	Vested at March 31, 2015					1,310	$	6.07		7.4	$	39,340
	The weighted-average grant-date estimated fair value of options granted during the three months ended March 31, 2015 and 2014 was $25.07 and $30.44, respectively. The aggregate intrinsic value of options outstanding and exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the NASDAQ listing fair value of the Company’s common stock as of March 31, 2015.
	Stock-Based Compensation Expense
	Stock-based compensation expense included in the Company’s consolidated statements of operations is as follows (in thousands):
		Three Months Ended March 31
		2015			2014
	Research and development:
	Employees	$	883		$	225
	Nonemployee consultants		1,238			1,209
	General and administrative:
	Employees		1,505			564
	Nonemployee consultants		—			—
	Total stock-based compensation expense	$	3,626		$	1,998
	As of March 31, 2015, the total unrecognized stock-based compensation expense related to stock options and ESPP stock repurchase rights was $33.3 million, which is expected to be recognized over an estimated weighted-average period of 2.87 years.
	The estimated grant date fair value of employee stock options was calculated using the Black-Scholes valuation model, based on the following assumptions:
		Three Months Ended March 31,
		2015			2014
	Expected volatility		87% - 92%			109%
	Expected dividends		0%			0%
	Expected term (in years)		6			6
	Risk-free rate		1.3% –1.8%			1.8% – 1.9%
	The fair value of nonemployee stock options was calculated using the Black-Scholes valuation model, based on the following assumptions:
		Three Months Ended March 31,
			2015		2014
	Expected volatility		91% - 92%			107%-122%
	Expected dividends		0%			0%
	Expected term (in years)		6 – 8			9-Jun
	Risk-free rate		1.5% – 1.8%			2.0%-2.6%
	Restricted Stock Units
	During 2014, the Company granted restricted stock unit (“RSUs”) awards subject to time-based vesting criteria from the 2013 Plan. RSUs subject to time-based vesting criteria entitle holders to receive shares of common stock at the end of a specified period of time. For RSUs subject to time-based vesting criteria, vesting is based on continuous employment or service of the holder to the Company. The fair value of RSUs is measured based on the number of shares granted and the closing market price of our common stock on the date of grant. The following table summarizes restricted stock unit activity for the three months ended March 31, 2015 (in thousands, except per share amounts):
		Restricted Stock Units
		Number of Shares			Weighted Average
					Grant Date Fair
					Value Per Share
	Nonvested at December 31, 2014		123		$	26.85
	Granted		—			—
	Vested		—			—
	Canceled		(1	)		27.21
	Nonvested at March 31, 2015		122		$	26.85
	As of March 31, 2015, none of the restricted stock units granted by the Company have vested.

Description_of_Business_and_Si1

Description of Business and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Organization	Organization
	Relypsa, Inc. (Relypsa or the Company) is a biopharmaceutical company dedicated to the development and commercialization of new non-absorbed polymeric drugs for important applications in renal, cardiovascular and metabolic disease. Relypsa’s lead product candidate is Patiromer for Oral Suspension, or Patiromer FOS. A new drug application has been filed with the U.S. Food and Drug Administration (FDA) for Patiromer FOS for the treatment of hyperkalemia and is currently under review. The FDA has assigned a Prescription Drug User Fee Act, or PDUFA, action date of October 21, 2015 for completion of review for the Company’s New Drug Application (NDA). The Company commenced operations on October 29, 2007. The Company’s principal operations are based in Redwood City, California and it operates in one segment. On October 28, 2014, Relypsa UK LTD was incorporated as a wholly-owned subsidiary of the Company.
	The information included in this quarterly report on Form 10-Q should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014 filed with the U.S. Securities Exchange Commission (SEC).
Offerings	Offerings
	On December 4, 2014, the Company filed a shelf registration statement on Form S-3, which permitted: (a) the offering, issuance and sale by the Company of up to a maximum aggregate offering price of $250.0 million of its common stock, preferred stock, debt securities, warrants, purchase contracts and/or units; and (b) as part of the $250.0 million, the offering, issuance and sale by the Company of up to a maximum aggregate offering price of $70.0 million of its common stock that may be issued and sold under a sales agreement with Cantor Fitzgerald & Co in one or more at-the-market offerings. As of December 31, 2014, the Company had sold 514,710 shares pursuant to its at-the-market program at an average price of $32.17 for aggregate offering proceeds of $16.6 million and the Company received aggregate net proceeds of $16.1 million.
	During January and February 2015, the Company sold 1,549,910 shares pursuant to the Company’s at-the-market program at an average price of $34.48 for aggregate offering proceeds of $53.4 million, and the Company received aggregate net proceeds of $51.8 million.  During the first quarter of 2015, the Company exhausted its current at-the-market offering in full.
	On March 3, 2015, the Company completed an underwritten public offering of 4,485,000 shares of common stock at an offering price of $38.50 per share for gross proceeds of $172.7 million. The Company received net proceeds from the offering of $161.9 million, after deducting the underwriting discounts and expenses.
Basis of Presentation	Basis of Presentation
	There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2015 as compared to the significant accounting policies described in the Company’s audited consolidated financial statements included in the Company’s Annual Report on Form 10-K filed with the SEC for the year ended December 31, 2014.
	The accompanying financial information for the three months ended March 31, 2015 is unaudited. These unaudited interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP and applicable rules and regulations of the SEC regarding interim financial reporting. Certain information and note disclosures normally included in the consolidated financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014, and include all adjustments, which include only normal recurring adjustments. Intercompany transactions and balances have been eliminated in consolidation. The results for the three months ended March 31, 2015 are not necessarily indicative of the results expected for the full fiscal year or any other period(s).
Use of Estimates	Use of Estimates
	The preparation of these unaudited interim condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and judgments that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, manufacturing accruals, fair value of assets and liabilities, common stock, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	In April 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-03, Simplifying the Presentation of Debt Issuance Costs. The update changes the presentation of debt issuance costs in financial statements. ASU 2015-03 requires an entity to present such costs in the balance sheet as a direct deduction from the related debt liability rather than an asset. Amortization of the costs will continue to be reported as interest expense. It is effective for annual reporting periods beginning after December 15, 2016. Implementation of this update will not have a material impact on the Company's consolidated financial statements.
Liquidity	Liquidity
	The Company has never been profitable and, as of March 31, 2015, the Company has an accumulated deficit of $335.4 million. The Company may continue to incur substantial operating losses even after it begins to generate meaningful revenues from Patiromer FOS, if approved. The Company will need additional funding to support future operating activities and adequate funding may not be available to the Company on acceptable terms, or at all. The Company’s failure to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition. The Company will need to generate significant revenues to achieve profitability and it may never do so.
Research and Development Expenses	Research and Development Expenses
	Research and development costs are charged to expense as incurred and consist of costs incurred to further the Company’s research and development activities including salaries and related employee benefits, costs associated with clinical trials, costs related to pre-commercialization manufacturing activities such as manufacturing process validation activities and the manufacturing of commercial supply prior to approval, nonclinical research and development activities, regulatory activities, research-related overhead expenses and fees paid to external service providers and contract research and manufacturing organizations that conduct certain research and development activities on behalf of the Company.
Net Loss per Common Share
	Net Loss per Common Share
	Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per common share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period using the treasury stock method.
	The following outstanding shares of common stock equivalents were excluded from the computations of diluted net loss per common share attributable to common stockholders for the periods presented as the effect of including such securities would be antidilutive (in thousands):
		March, 31
		2015		2014
	Warrants to purchase common stock		15		64
	Options to purchase common stock		3,731		3,610
	Restricted stock units		122		5
	Common stock subject to repurchase		1		4
			3,869		3,683

Description_of_Business_and_Si2

Description of Business and Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Schedule of Shares Excluded from Computations of Diluted Net Loss per Common Share	The following outstanding shares of common stock equivalents were excluded from the computations of diluted net loss per common share attributable to common stockholders for the periods presented as the effect of including such securities would be antidilutive (in thousands):
		March, 31
		2015		2014
	Warrants to purchase common stock		15		64
	Options to purchase common stock		3,731		3,610
	Restricted stock units		122		5
	Common stock subject to repurchase		1		4
			3,869		3,683

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments Measured at Fair Value on Recurring Basis	The following tables set forth the fair value of the Company’s financial instruments that were measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 (in thousands):
		Level 1			Level 2		Level 3		Total
	31-Mar-15
	Financial assets:
	Money market funds	$	15,648		$	—	$	—	$	15,648
	Corporate bonds		—			146,683		—		146,683
	Agency bonds		—			61,538		—		61,538
	Commercial paper		—			96,801		—		96,801
	Total financial assets	$	15,648		$	305,022	$	—	$	320,670
	Liabilities:
	Contingent put option liability	$	—		$	—	$	233	$	233
	Total liabilities	$	—		$	—	$	233	$	233
		Level 1			Level 2		Level 3		Total
	31-Dec-14
	Financial assets:
	Money market funds	$	10,202		$	—	$	—	$	10,202
	Corporate bonds		—			71,763		—		71,763
	Agency bonds		—			15,162		—		15,162
	Commercial paper		—			30,846		—		30,846
	Total financial assets	$	10,202		$	117,771	$	—	$	127,973
	Liabilities:
	Contingent put option liability	$	—		$	—	$	233	$	233
	Total liabilities	$	—		$	—	$	233	$	233
Summary of Changes in Estimated Fair Value of Level 3 Instruments Measured at Fair Value on Recurring Basis	As of March 31, 2015, the Company’s Level 3 liability is comprised of a contingent put option liability. The following table sets forth a summary of the changes in the estimated fair value of the Company’s contingent put option, which are measured at fair value on a recurring basis (in thousands):
	Balance as of December 31, 2014		$	233
	Decrease in fair value included in other income (expense)			—
	Balance as of March 31, 2015		$	233

Cash_Cash_Equivalents_and_Inve1

Cash, Cash Equivalents, and Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Cash And Cash Equivalents [Abstract]
Summary of Cash, Cash Equivalents, and Investments	The following is a summary of cash, cash equivalents, and investments (in thousands):
		Amortized		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair
				Gains		Losses			Value
	31-Mar-15
	Cash and money market funds	$	19,305	$	—	$	—		$	19,305
	Corporate bonds		146,709		10		(36	)		146,683
	Agency bonds		61,541		3		(6	)		61,538
	Commercial paper		96,768		33		—			96,801
	Total financial assets	$	324,323	$	46	$	(42	)	$	324,327
	Reported as:
	Cash and cash equivalents								$	82,771
	Investments									241,556
									$	324,327
		Amortized		Gross		Gross			Estimated
		Cost		Unrealized		Unrealized			Fair
				Gains		Losses			Value
	31-Dec-14
	Cash and money market funds	$	17,986	$	—	$	—		$	17,986
	Corporate bonds		71,794		2		(33	)		71,763
	Agency bonds		15,163		2		(3	)		15,162
	Commercial paper		30,835		11		—			30,846
	Total financial assets	$	135,778	$	15	$	(36	)	$	135,757
	Reported as:
	Cash and cash equivalents								$	30,264
	Investments									105,493
									$	135,757

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments Under Supply Agreement	The following are the combined future minimum payments under the terms of the Lanxess Supply Agreement, the DPx Supply Agreement, and the Patheon Supply Agreement as of March 31, 2015.  These amounts are based on forecasts that include estimates of future market demand, quantity discounts and manufacturing efficiencies (in thousands):
	2015	$	41,756
	2016		46,900
	2017		37,800
	2018		42,400
	2019		42,201
	Thereafter		22,000
	Total future minimum payments	$	233,057
Schedule of Future Minimum Payments Under Operating Lease	Future minimum operating lease payments at March 31, 2015 are as follows (in thousands):
	2015	$	1,805
	2016		3,209
	2017		3,373
	2018		3,449
	2019		3,544
	Thereafter		20,064
	Total future minimum payments	$	35,444

Equity_Compensation_Plans_and_1

Equity Compensation Plans and Stock Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Option Activity Under 2007 Plan 2013 Plan and Inducement Plan and Related Information	The following table summarizes option activity under the 2007 Plan, the 2013 Plan, the Inducement Plan, and related information (in thousands, except per share and contractual term amounts):
		Shares			Shares Subject		Weighted-		Weighted-		Aggregate
		Available			to Outstanding		Average		Average		Intrinsic
		for			Options		Exercise Price		Remaining		Value
		Grant					Per Share		Contractual
									Term
									(in years)
	Options Outstanding at December 31, 2014		1,167			3,813	$	11.05
	Additional shares reserved under plan		1,402			—		—
	Options granted		(263	)		263		33.34
	Options exercised		—			-304		4.59
	Options forfeited		41			-41		22.4
	Restricted Stock Units canceled		1			—		—
	Balances at March 31, 2015		2,348			3,731	$	13.02		8.3	$	86,287
	Vested and expected to vest at March 31, 2015					3,579	$	12.72		8.2	$	83,850
	Vested at March 31, 2015					1,310	$	6.07		7.4	$	39,340
Schedule of Stock-Based Compensation Expense	Stock-based compensation expense included in the Company’s consolidated statements of operations is as follows (in thousands):
		Three Months Ended March 31
		2015			2014
	Research and development:
	Employees	$	883		$	225
	Nonemployee consultants		1,238			1,209
	General and administrative:
	Employees		1,505			564
	Nonemployee consultants		—			—
	Total stock-based compensation expense	$	3,626		$	1,998
Summary of Restricted Stock Unit Activity	The following table summarizes restricted stock unit activity for the three months ended March 31, 2015 (in thousands, except per share amounts):
		Restricted Stock Units
		Number of Shares			Weighted Average
					Grant Date Fair
					Value Per Share
	Nonvested at December 31, 2014		123		$	26.85
	Granted		—			—
	Vested		—			—
	Canceled		(1	)		27.21
	Nonvested at March 31, 2015		122		$	26.85
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Schedule of Valuation Assumptions Used to Calculate Fair Value of Stock Options	The estimated grant date fair value of employee stock options was calculated using the Black-Scholes valuation model, based on the following assumptions:
		Three Months Ended March 31,
		2015			2014
	Expected volatility		87% - 92%			109%
	Expected dividends		0%			0%
	Expected term (in years)		6			6
	Risk-free rate		1.3% –1.8%			1.8% – 1.9%
Non Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Schedule of Valuation Assumptions Used to Calculate Fair Value of Stock Options	The fair value of nonemployee stock options was calculated using the Black-Scholes valuation model, based on the following assumptions:
		Three Months Ended March 31,
			2015		2014
	Expected volatility		91% - 92%			107%-122%
	Expected dividends		0%			0%
	Expected term (in years)		6 – 8			9-Jun
	Risk-free rate		1.5% – 1.8%			2.0%-2.6%

Description_of_Business_and_Si3

Description of Business and Significant Accounting Policies - Additional Information (Details) (USD $)	0 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended
	Mar. 03, 2015	Feb. 28, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 04, 2014
			Segment
Description Of Business And Significant Accounting Policies [Line Items]
Commencement date of operations			29-Oct-07
Number of business segments			1
Issuance of common stock, shares		1,549,910
Shares issued, price per share		$34.48
Gross proceeds from issuance of common stock	$172,700,000	$53,400,000
Aggregate net proceeds from issuance of common stock	161,900,000	51,800,000	213,711,000
Accumulated deficit	335,400,000		-335,393,000	-305,728,000
Common Stock
Description Of Business And Significant Accounting Policies [Line Items]
Issuance of common stock, shares	4,485,000
Shares issued, price per share	$38.50
Shelf Registration | Maximum
Description Of Business And Significant Accounting Policies [Line Items]
Aggregate offering price					250,000,000
Shelf Registration | Common Stock | Maximum
Description Of Business And Significant Accounting Policies [Line Items]
Aggregate offering price					70,000,000
Shelf Registration
Description Of Business And Significant Accounting Policies [Line Items]
Issuance of common stock, shares				514,710
Shares issued, price per share				$32.17
Gross proceeds from issuance of common stock				16,600,000
Aggregate net proceeds from issuance of common stock				$16,100,000
Relypsa UK LTD
Description Of Business And Significant Accounting Policies [Line Items]
Date of entity incorporation			28-Oct-14

Description_of_Business_and_Si4

Description of Business and Significant Accounting Policies - Schedule of Shares Excluded from Computations of Diluted Net Loss per Common Share (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computations of diluted net loss per common share	3,869,000	3,683,000
Warrants To Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computations of diluted net loss per common share	15,000	64,000
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computations of diluted net loss per common share	3,731,000	3,610,000
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computations of diluted net loss per common share	122,000	5,000
Common Stock Subject to Repurchase
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computations of diluted net loss per common share	1,000	4,000

Fair_Value_Measurements_Fair_V

Fair Value Measurements - Fair Value of Financial Instruments Measured at Fair Value on Recurring Basis (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Financial assets:
Total financial assets	$320,670	$127,973
Liabilities:
Total liabilities	233	233
Contingent Put Option Liability
Liabilities:
Total liabilities	233	233
Level 1
Financial assets:
Total financial assets	15,648	10,202
Level 2
Financial assets:
Total financial assets	305,022	117,771
Level 3
Liabilities:
Total liabilities	233	233
Level 3 | Contingent Put Option Liability
Liabilities:
Total liabilities	233	233
Corporate Bonds
Financial assets:
Total financial assets	146,683	71,763
Corporate Bonds | Level 2
Financial assets:
Total financial assets	146,683	71,763
Agency Bonds
Financial assets:
Total financial assets	61,538	15,162
Agency Bonds | Level 2
Financial assets:
Total financial assets	61,538	15,162
Money Market Funds
Financial assets:
Total financial assets	15,648	10,202
Money Market Funds | Level 1
Financial assets:
Total financial assets	15,648	10,202
Commercial Paper
Financial assets:
Total financial assets	96,801	30,846
Commercial Paper | Level 2
Financial assets:
Total financial assets	$96,801	$30,846

Fair_Value_Measurements_Summar

Fair Value Measurements - Summary of Changes in Estimated Fair Value of Level 3 Instruments Measured at Fair Value on Recurring Basis (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Debt Instrument Fair Value Carrying Value [Abstract]
Beginning Balance	$233	$233
Ending Balance	$233	$233

Cash_Cash_Equivalents_and_Inve2

Cash, Cash Equivalents, and Investments - Summary of Cash, Cash Equivalents, and Investments (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Cash And Cash Equivalents [Line Items]
Amortized Cost	$324,323	$135,778
Gross Unrealized Gains	46	15
Gross Unrealized Losses	-42	-36
Estimated Fair Value	324,327	135,757
Cash and cash equivalents	82,771	30,264	26,098	94,759
Investments	241,556	105,493
Total financial assets	324,327	135,757
Cash and Money Market Funds
Cash And Cash Equivalents [Line Items]
Amortized Cost	19,305	17,986
Estimated Fair Value	19,305	17,986
Commercial Paper
Cash And Cash Equivalents [Line Items]
Amortized Cost	96,768	30,835
Gross Unrealized Gains	33	11
Estimated Fair Value	96,801	30,846
Corporate Bonds
Cash And Cash Equivalents [Line Items]
Amortized Cost	146,709	71,794
Gross Unrealized Gains	10	2
Gross Unrealized Losses	-36	-33
Estimated Fair Value	146,683	71,763
Agency Bonds
Cash And Cash Equivalents [Line Items]
Amortized Cost	61,541	15,163
Gross Unrealized Gains	3	2
Gross Unrealized Losses	-6	-3
Estimated Fair Value	$61,538	$15,162

Cash_Cash_Equivalents_and_Inve3

Cash, Cash Equivalents, and Investments - Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Cash And Cash Equivalents [Abstract]
Realized gain or losses on available-for-sale securities	$0	$0
Available-for-sale securities, current	239,600,000
Available-for-sale securities, noncurrent	2,000,000
Available for sale securities, continuous unrealized loss position for more than one year	$0

Borrowings_Additional_Informat

Borrowings - Additional Information (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	30-May-14	31-May-13	Jan. 31, 2013
Debt Instrument [Line Items]
Line of credit amount				$1,600,000
Line of credit, terms of repayment	The terms of repayment are 36 monthly payments
Line of credit, interest rate	5.75%
Line of credit, remaining and expired amount	300,000
Line of credit, expiry date	30-Jun-13
Line of credit principal amount outstanding	500,000
Line of Credit
Debt Instrument [Line Items]
Number of debt repayments	36
Final payment as a percentage of amounts borrowed	9.25%
Warrant issued to purchase common stock	3,998
Fair value of warrants	25,000
Warrants, fair value assumptions, interest rate	1.07%
Warrants, fair value assumptions, expected life	7 years
Warrants, fair value assumptions, volatility factor	91.60%
Warrants, fair value assumptions, dividend yield	0.00%
Interest expense	21,000	46,000
Line of credit, utilized amount	1,300,000
Series C Preferred Stock | Line of Credit
Debt Instrument [Line Items]
Warrants issued to purchase preferred stock				6,968
Capital Loan
Debt Instrument [Line Items]
Proceeds From Issuance Of Long Term Debt	15,000,000		15,000,000
Repayment of outstanding debt	11,000,000
Final payment fee	400,000
Advance not yet received	20,000,000
Debt instrument, payment terms	Payments on the new $15.0 million loan will be interest only through January 2016, followed by 30 months of equal monthly payments of interest and principal
Number of debt repayments	30
Final payment as a percentage of amounts borrowed	8.50%
Exercise price of warrants			$23.69
Warrants exercised	40,828	13,609
Warrant issued to purchase common stock	29,690	7,808	12,661
Fair value of warrants	200,000
Warrants, fair value assumptions, interest rate	2.06%
Warrants, fair value assumptions, expected life	7 years
Warrants, fair value assumptions, volatility factor	91.67%
Warrants, fair value assumptions, dividend yield	0.00%
Interest expense	500,000	400,000
Estimated fair value of contingent put option liability	200,000
Principal amount outstanding on loan	$15,000,000
Capital Loan | Minimum
Debt Instrument [Line Items]
Prepayment charges of outstanding loan	1.00%
Capital Loan | Maximum
Debt Instrument [Line Items]
Prepayment charges of outstanding loan	3.00%
Capital Loan | Series C Preferred Stock
Debt Instrument [Line Items]
Warrants issued to purchase preferred stock					54,437
Exercise price of warrants					$9.18
Capital Loan | Initial advance
Debt Instrument [Line Items]
Debt instrument, interest rate	7.40%
Capital Loan | Three Month LIBOR Rate | Second Tranche
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	7.17%

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Commitments And Contingencies [Line Items]
Supply agreement term	The Lanxess Supply Agreement terminates on December 31, 2020 unless terminated earlier. The Company may extend the Lanxess Supply Agreement for an additional five years with notice.
Agreement termination date	31-Dec-20
Extended agreement period	5 years
Additional lease allowance	$2.20
One-time lease improvement allowance	0.6
Lease commencement date	1-Feb-15
Operating lease, term of contract	10 years
Operating lease, renewal term	5 years
Irrevocable Letter of Credit
Commitments And Contingencies [Line Items]
Security deposit	$0.70
Patheon Inc
Commitments And Contingencies [Line Items]
Supply agreement term	The Patheon Supply Agreement may be terminated by the Company with written notice under certain provisions.

Commitments_and_Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments Under Supply Agreement(Details) (DPx Fine Chemicals, Lanxess and Patheon, USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
DPx Fine Chemicals, Lanxess and Patheon
Long Term Purchase Commitment [Line Items]
2015	$41,756
2016	46,900
2017	37,800
2018	42,400
2019	42,201
Thereafter	22,000
Total future minimum payments	$233,057

Commitments_and_Contingencies_3

Commitments and Contingencies - Schedule of Future Minimum Payments Under Operating Lease (Details) (USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]
2015	$1,805
2016	3,209
2017	3,373
2018	3,449
2019	3,544
Thereafter	20,064
Total future minimum payments	$35,444

Equity_Compensation_Plans_and_2

Equity Compensation Plans and Stock Based Compensation - Additional Information (Details) (USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant-date fair value of options grant	$25.07	$30.44
Unrecognized compensation cost	$33.30
Expected period of compensation expense recognized	2 years 10 months 13 days
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units, vested	0
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance	587,438
2007 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted period	10 years
Option vest over period	4 years
2013 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted period	10 years
Share-based compensation description	Options granted under the 2013 Plan may be granted for periods of up to ten years and are generally exercisable when vested. Any remaining shares available for future issuance under the 2007 Stock Plan are available for issuance under the 2013 Plan. The 2013 plan reserve will automatically increase annually from January 1, 2014 through January 1, 2023 by an amount equal to the smaller of: (a) 2,553,174 shares, (b) four percent of the number of shares of common stock issued and outstanding on the immediately preceding December 31, or (c) an amount determined by the Company's board of directors.
Increase of shares reserve under the plan	2,553,174
Percentage of common stock issued and outstanding	4.00%
Beginning date for increase in share reserve	1-Jan-14
Ending date for increase in share reserve	1-Jan-23
Share-based compensation authorized	1,963,355
2014 Employment Commencement Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for inducement options			1,000,000
Share issued or transferred under the Plan	614,600

Equity_Compensation_Plans_and_3

Equity Compensation Plans and Stock Based Compensation - Summary of Option Activity Under 2007 Plan 2013 Plan and Inducement Plan and Related Information (Details) (2007 Plan, 2013 Plan and Inducement Plan, USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015
2007 Plan, 2013 Plan and Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Available for Grant, Options Outstanding, beginning balance	1,167,000
Shares Available for Grant, Additional shares reserved	1,402,000
Shares Available for Grant, Options granted	-263,000
Shares Available for Grant, Options forfeited	41,000
Shares Available for Grant, Restricted stock units cancelled	1,000
Shares Available for Grant, Options Outstanding, ending balance	2,348,000
Shares Subject to Outstanding Options, Options Outstanding, beginning balance	3,813,000
Shares Subject to Outstanding Options, Options granted	263,000
Shares Subject to Outstanding Options, Options exercised	-304,000
Shares subject to Outstanding Options, Options forfeited	-41,000
Shares Subject to Outstanding Options, Options Outstanding, ending balance	3,731,000
Shares Subject to Outstanding Options, Vested and expected to vest	3,579,000
Shares Subject to Outstanding Options, Vested	1,310,000
Weighted-Average Exercise Price Per Share, Options Outstanding, beginning balance	$11.05
Weighted-Average Exercise Price Per Share, Options granted	$33.34
Weighted-Average Exercise Price Per Share, Options exercised	$4.59
Weighted-Average Exercise Price Per Share, Options forfeited	$22.40
Weighted-Average Exercise Price Per Share, Options Outstanding, ending balance	$13.02
Weighted-Average Exercise Price Per Share, Vested and expected to vest	$12.72
Weighted-Average Exercise Price Per Share, Vested	$6.07
Weighted-Average Remaining Contractual Term, Options Outstanding	8 years 3 months 18 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	8 years 2 months 12 days
Weighted-Average Remaining Contractual Term, Vested	7 years 4 months 24 days
Aggregate Intrinsic Value, Options Outstanding	$86,287
Aggregate Intrinsic Value, Vested and expected to vest	83,850
Aggregate intrinsic value, Vested	$39,340

Equity_Compensation_Plans_and_4

Equity Compensation Plans and Stock Based Compensation - Schedule of Stock-Based Compensation Expense (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$3,626	$1,998
Research and Development | Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	883	225
Research and Development | Non-employee Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	1,238	1,209
General and Administrative | Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$1,505	$564

Equity_Compensation_Plans_and_5

Equity Compensation Plans and Stock Based Compensation - Schedule of Valuation Assumptions Used to Calculate Fair Value of Employee Stock Options (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility		109.00%
Expected dividends	0.00%	0.00%
Expected term (in years)	6 years	6 years
Risk-free rate, minimum	1.30%	1.80%
Risk-free rate, maximum	1.80%	1.90%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	87.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	92.00%

Equity_Compensation_Plans_and_6

Equity Compensation Plans and Stock Based Compensation - Schedule of Valuation Assumptions Used to Calculate Fair Value of Nonemployee Stock Options (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividends	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	91.00%	107.00%
Expected term (in years)	6 years	6 years
Risk-free rate	1.50%	2.00%
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	92.00%	122.00%
Expected term (in years)	8 years	9 years
Risk-free rate	1.80%	2.60%

Equity_Compensation_Plans_and_7

Equity Compensation Plans and Stock Based Compensation - Summary of Restricted Stock Unit Activity (Details) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015
Compensation Related Costs [Abstract]
Number of Shares, Nonvested at Beginning	123
Number of Shares, Canceled	-1
Number of Shares, Nonvested at Ending	122
Weighted Average Grant Date Fair Value Per Share, Nonvested at Beginning	$26.85
Weighted Average Grant Date Fair Value Per Share, Canceled	$27.21
Weighted Average Grant Date Fair Value Per Share, Nonvested at Ending	$26.85