Keryx Biopharmaceuticals (KERX) 10-Q 8 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	1-May-14
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Trading Symbol	'KERX	'
Entity Registrant Name	'KERYX BIOPHARMACEUTICALS INC	'
Entity Central Index Key	'0001114220	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	91,452,573

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$105,257	$55,696
Short-term investment securities	49,665	'
Interest receivable	195	'
Other current assets	1,245	1,232
Total current assets	156,362	56,928
Property, plant and equipment, net	538	349
Goodwill	3,208	3,208
Other assets, net	217	281
Total assets	160,325	60,766
Current liabilities:	'	'
Accounts payable and accrued expenses	15,955	14,004
Accrued compensation and related liabilities	414	1,324
Total current liabilities	16,369	15,328
Other liabilities	41	38
Total liabilities	16,410	15,366
Commitments and contingencies	'	'
Stockholders' equity:	'	'
Preferred stock, $0.001 par value per share (5,000,000 shares authorized, no shares issued and outstanding)	'	'
Common stock, $0.001 par value per share (130,000,000 shares authorized, 91,335,160 and 82,723,145 shares issued, 91,255,212 and 82,643,197 shares outstanding at March 31, 2014 and December 31, 2013, respectively)	91	83
Additional paid-in capital	597,051	485,014
Treasury stock, at cost, 79,948 shares at March 31, 2014 and December 31, 2013, respectively	-357	-357
Accumulated deficit	-452,870	-439,340
Total stockholders' equity	143,915	45,400
Total liabilities and stockholders' equity	$160,325	$60,766

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	'	'
Preferred stock, shares outstanding	'	'
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares issued	91,335,160	82,723,145
Common stock, shares outstanding	91,255,212	82,643,197
Treasury stock, shares	79,948	79,948

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
License revenue	$10,000	$7,000
Research and development:	'	'
Non-cash compensation	804	191
Other research and development	15,555	6,239
Total research and development	16,359	6,430
General and administrative:	'	'
Non-cash compensation	1,748	390
Other general and administrative	5,544	2,338
Total general and administrative	7,292	2,728
Total operating expenses	23,651	9,158
Operating loss	-13,651	-2,158
Interest and other income, net	121	103
Loss before income taxes	-13,530	-2,055
Income taxes	'	'
Net loss	($13,530)	($2,055)
Basic and diluted net loss per common share	($0.15)	($0.03)
Weighted average shares used in computing basic and diluted net loss per common share	88,517,437	77,990,094

Consolidated_Statement_of_Stoc

Consolidated Statement of Stockholders' Equity (USD $)	Total		Common stock		Additional paid-in capital	Treasury stock	Accumulated deficit
In Thousands, except Share data, unless otherwise specified
Beginning Balance at Dec. 31, 2013	$45,400		$83		$485,014	($357)	($439,340)
Beginning Balance (in shares) at Dec. 31, 2013	'		82,723,145		'	79,948	'
Changes during the period:	'		'		'	'	'
Issuance of common stock in public offering (net of offering costs of $7,460) (in shares)	'		7,935,000		'	'	'
Issuance of common stock in public offering (net of offering costs of $7,460)	107,597		8		107,589	'	'
Issuance of restricted stock (in shares)	'		386,958		'	'	'
Issuance of restricted stock	'	[1]	'	[1]	'	'	'
Forfeiture of restricted stock ( in shares )	'		-15,791		'	'	'
Forfeiture of restricted stock	'	[1]	'	[1]	'	'	'
Issuance of common stock in connection with exercise of options (in shares)	'		305,848		'	'	'
Issuance of common stock in connection with exercise of options	1,896		'		1,896	'	'
Compensation in respect of options and restricted stock granted to employees, directors and third-parties	2,552		'		2,552	'	'
Net loss	-13,530		'		'	'	-13,530
Ending Balance at Mar. 31, 2014	$143,915		$91		$597,051	($357)	($452,870)
Ending Balance (in shares) at Mar. 31, 2014	'		91,335,160		'	79,948	'
[1]	Amount less than one thousand dollars.

Consolidated_Statement_of_Stoc1

Consolidated Statement of Stockholders' Equity (Parenthetical) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
Issuance of common stock in public offering, offering costs	$7,460

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES	'	'
Net loss	($13,530)	($2,055)
Adjustments to reconcile net loss to cash flows used in operating activities:	'	'
Stock compensation expense	2,552	581
Depreciation and amortization	32	10
Changes in assets and liabilities:	'	'
Increase in other current assets	-13	-1,314
Increase in accrued interest receivable	-195	'
Decrease in other assets	64	35
Increase in accounts payable and accrued expenses	1,951	1,242
Decrease in accrued compensation and related liabilities	-910	-625
Increase (decrease) in other liabilities	3	-12
Net cash used in operating activities	-10,046	-2,138
CASH FLOWS FROM INVESTING ACTIVITIES	'	'
Purchases of property, plant and equipment	-221	-45
Investment in held-to-maturity short-term securities	-49,772	'
Proceeds from maturity of held-to-maturity short-term securities	107	'
Net cash used in investing activities	-49,886	-45
CASH FLOWS FROM FINANCING ACTIVITIES	'	'
Gross proceeds from public offerings	115,057	80,393
Offering costs related to public offerings	-7,460	-5,637
Proceeds from exercise of options	1,896	93
Net cash provided by financing activities	109,493	74,849
NET INCREASE IN CASH AND CASH EQUIVALENTS	49,561	72,666
Cash and cash equivalents at beginning of period	55,696	14,677
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$105,257	$87,343

General

General	3 Months Ended
	Mar. 31, 2014
General	'
	NOTE 1 - GENERAL
	Basis of Presentation
	We are a biopharmaceutical company focused on focused on bringing innovative therapies to market for patients suffering from renal disease. Most of our biopharmaceutical development and substantially all of our administrative operations during the three months ended March 31, 2014 and 2013 were conducted in the United States of America.
	The accompanying unaudited consolidated financial statements were prepared in accordance with U.S. generally accepted accounting principles (“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 the consolidated financial statements have been included. Nevertheless, these unaudited 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, 2013. The results of operations for the three months ended March 31, 2014, are not necessarily indicative of the results that may be expected for the entire fiscal year or any other interim period.
	Except for 2009, we have incurred substantial operating losses since our inception, and expect to continue to incur operating losses for the foreseeable future and may never become profitable. As of March 31, 2014, we have an accumulated deficit of $452.9 million.
	Our major sources of cash have been proceeds from various public and private offerings of our common stock, option and warrant exercises, interest income, and from the upfront and milestone payments from our Sublicense Agreement with Japan Tobacco Inc. (“JT”) and Torii Pharmaceutical Co., Ltd. (“Torii”) and miscellaneous payments from our other prior licensing activities. We have not yet commercialized any drug candidate and cannot be sure if we will ever be able to do so. Even if we commercialize a drug candidate, we may not become profitable. Our ability to achieve profitability depends on a number of factors, including our ability to complete our development efforts, obtain regulatory approval for our drug candidate, successfully complete any post-approval regulatory obligations and successfully manufacture and commercialize our drug candidate alone or in partnership. We may continue to incur substantial operating losses even if we begin to generate revenues from our drug candidate, if approved.
	We have completed a U.S.-based Phase 3 clinical program for Zerenex for the treatment of hyperphosphatemia (elevated phosphate levels) in patients with chronic kidney disease, or CKD, on dialysis, conducted pursuant to a Special Protocol Assessment, or SPA, agreement with the U.S. Food and Drug Administration, or FDA. Our New Drug Application, or NDA, is currently under review by the FDA with an assigned Prescription Drug User Fee Act, or PDUFA, goal date of June 7, 2014. In addition, in March 2014, we submitted a Marketing Authorization Application, or MAA, with the European Medicines Agency, or EMA, seeking the approval of Zerenex as a treatment for hyperphosphatemia in patients with CKD, including dialysis and non-dialysis dependent CKD, or NDD-CKD. Also in March 2014, the EMA validated our MAA, confirming that the submission is sufficiently complete to begin the formal review process.
	We have also completed a U.S.-based Phase 2 study of Zerenex for the management of elevated serum phosphorus levels and iron deficiency anemia in subjects with Stage 3 to 5 NDD-CKD.
	In January 2014, we raised approximately $107.6 million, net of underwriting discounts and offering expenses of approximately $7.5 million, in an underwritten public offering. We have a shelf registration statement on Form S-3 filed and declared effective by the Securities and Exchange Commission in August 2013, which provides for the offering of up to $150 million of common stock and warrants in the aggregate. Subsequent to the underwritten public offering completed in January 2014, there remains approximately $34.9 million of our common stock and warrants available for sale on this shelf registration statement. See Note 3 for additional information.
	In January 2014, our Japanese partner, JT and Torii, received manufacturing and marketing approval of ferric citrate from the Japanese Ministry of Health, Labour and Welfare. Ferric citrate, to be marketed in Japan by JT’s subsidiary, Torii, under the brand name Riona®, is indicated as an oral treatment for the improvement of hyperphosphatemia in patients with CKD, including dialysis and NDD-CKD. Under the license agreement with JT and Torii, Keryx received a non-refundable payment of $10.0 million in February 2014 for the achievement of the marketing approval milestone. Keryx will also receive double-digit tiered royalties on net sales of Riona® in Japan, as well as up to an additional $55.0 million upon the achievement of certain annual net sales milestones. See Note 4 for additional information.
	We currently expect that our existing capital resources combined with future anticipated cash flows will be sufficient to operate our business plan. The actual amount of cash that we will need to operate is subject to many factors, including, but not limited to, the timing and expenditures associated with the build-up of pre-launch/launch inventory and capacity expansion, the timing and expenditures associated with the respective regulatory review processes for our U.S. NDA and EU MAA filings, the timing and expenditures associated with pre-commercial/commercial activities related to Zerenex, and the timing, design and conduct of clinical trials for Zerenex. We may depend upon significant additional financings to provide the cash necessary to execute our current operations, including the commercialization of Zerenex.
	Our common stock is listed on the NASDAQ Capital Market and trades under the symbol “KERX.”
	Cash and Cash Equivalents
	We treat liquid investments with original maturities of three months or less when purchased as cash and cash equivalents.
	Investment Securities
	We classify our short-term debt securities as held-to-maturity. Held-to-maturity securities are those securities in which we have the ability and intent to hold the security until maturity. Held-to-maturity securities are recorded at amortized cost, adjusted for the amortization or accretion of premiums or discounts. Premiums and discounts are amortized or accreted over the life of the related held-to-maturity security as an adjustment to yield using the effective interest method. Available-for-sale investment securities are recorded at fair value (see Note 2 – Fair Value Measurements). Other-than-temporary impairment charges are included in interest and other income, net, and unrealized gains (losses), if determined to be temporary, are included in accumulated other comprehensive income (loss) in stockholders’ equity.
	The following table summarizes our investment securities at March 31, 2014, and December 31, 2013:
	(in thousands)	March 31, 2014		December 31, 2013
	Short-term investments (held to maturity):
	Obligations of domestic governmental agencies (mature between May 2014 and January 2015)	$	49,665	$	—
	Total short-term investment securities	$	49,665	$	—
	Revenue Recognition
	We recognize license revenue in accordance with the revenue recognition guidance of the FASB Accounting Standards Codification (the “Codification”). We analyze each element of our licensing agreement to determine the appropriate revenue recognition. The terms of the license agreement may include payments to us of non-refundable up-front license fees, milestone payments if specified objectives are achieved, and/or royalties on product sales. We recognize revenue from upfront payments over the period of significant involvement under the related agreements unless the fee is in exchange for products delivered or services rendered that represent the culmination of a separate earnings process and no further performance obligation exists under the contract. We recognize milestone payments as revenue upon the achievement of specified milestones only if (1) the milestone payment is non-refundable, (2) substantive effort is involved in achieving the milestone, (3) the amount of the milestone is reasonable in relation to the effort expended or the risk associated with achievement of the milestone, and (4) the milestone is at risk for both parties. If any of these conditions are not met, we defer the milestone payment and recognize it as revenue over the estimated period of performance under the contract.
	Stock-Based Compensation
	We recognize all share-based payments to employees and to non-employee directors for service on our board of directors as compensation expense in the consolidated financial statements based on the grant date fair values of such payments. Stock-based compensation expense recognized each period is based on the value of the portion of share-based payment awards that is ultimately expected to vest during the period. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	For share-based payments to consultants and other third-parties, compensation expense is determined at the “measurement date.” The expense is recognized over the vesting period of the award. Until the measurement date is reached, the total amount of compensation expense remains uncertain. We record compensation expense based on the fair value of the award at the reporting date. The awards to consultants and other third-parties are then revalued, or the total compensation is recalculated based on the then current fair value, at each subsequent reporting date.
	Income Taxes
	As of March 31, 2014, we have U.S. net operating loss carryforwards of approximately $411.1 million which expire from 2019 through 2033. We have established a 100% valuation allowance against our net deferred tax assets due to our history of pre-tax losses and the likelihood that the deferred tax assets will not be realizable. Due to our historical equity transactions, the utilization of certain tax loss carryforwards may be subject to annual limitations imposed by Internal Revenue Code Section 382 relating to the change of control provisions.
	We are not aware of any unrecorded tax liabilities which would impact our financial position or our results of operations.
	Net Loss Per 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 options outstanding as of March 31, 2014 and 2013, which are not included in the computation of net loss per share amounts, were 4,360,925 and 3,882,100, respectively.
	Comprehensive Loss
	Comprehensive loss is the same as net loss for all periods presented.
	Segment Reporting
	We operate in only one reportable segment: the Products segment.
	Impairment of Goodwill
	Goodwill is reviewed for impairment annually, or when events arise that could indicate that an impairment exists. We test for goodwill impairment using a two-step process. The first step compares the fair value of the reporting unit with the unit’s carrying value, including goodwill. When the carrying value of the reporting unit is greater than fair value, the unit’s goodwill may be impaired, and the second step must be completed to measure the amount of the goodwill impairment charge, if any. In the second step, the implied fair value of the reporting unit’s goodwill is compared with the carrying amount of the unit’s goodwill. If the carrying amount is greater than the implied fair value, the carrying value of the goodwill must be written down to its implied fair value. As of December 31, 2013, management concluded that there was no impairment of our goodwill. As of March 31, 2014, management determined that there were no impairment indicators that would trigger a goodwill impairment analysis.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
Fair Value Measurements	'
	NOTE 2 - FAIR VALUE MEASUREMENTS
	We measure certain financial assets and liabilities at fair value on a recurring basis in the financial statements. The hierarchy ranks the quality and reliability of inputs, or assumptions, used in the determination of fair value and requires financial assets and liabilities carried at fair value to be classified and disclosed in one of the following three categories:
		•		Level 1 – quoted prices in active markets for identical assets and liabilities;
		•		Level 2 – inputs other than Level 1 quoted prices that are directly or indirectly observable; and
		•		Level 3 – unobservable inputs that are not corroborated by market data.
	We review investment securities for impairment and to determine the classification of the impairment as temporary or other-than-temporary. Losses are recognized in our consolidated statement of operations when a decline in fair value is determined to be other-than-temporary. We review our investments on an ongoing basis for indications of possible impairment. Once identified, the determination of whether the impairment is temporary or other-than-temporary requires significant judgment.
	The following table provides the fair value measurements of applicable financial assets as of March 31, 2014:
			Financial assets at fair value
			as of March 31, 2014
	(in thousands)		Level 1		Level 2		Level 3
	Money market funds (1)		$	73,755	$	—	$	—
	Obligations of domestic governmental agencies (held-to-maturity) (2)			49,665		—		—
	Total		$	123,420	$	—	$	—
	-1	Included in cash and cash equivalents on our consolidated balance sheet. The carrying amount of money market funds is a reasonable estimate of fair value.
	-2	Amortized cost approximates fair value.

Stockholders_Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2014
Stockholders' Equity	'
	NOTE 3 - STOCKHOLDERS’ EQUITY
	Common Stock
	On January 22, 2014, we announced the pricing of an underwritten public offering, whereby we sold 7,935,000 shares of our common stock at a price of $14.50 per share for gross proceeds of approximately $115.1 million. Net proceeds from this offering were approximately $107.6 million, net of underwriting discounts and offering expenses of approximately $7.5 million. The shares were sold under a Registration Statement (No. 333-190353) on Form S-3, filed by us with the Securities and Exchange Commission. This shelf registration statement on Form S-3, filed and declared effective by the SEC in August 2013, provides for the offering of up to $150 million of common stock and warrants in the aggregate. Subsequent to this underwritten public offering, there remains approximately $34.9 million of our common stock and warrants available for sale on this shelf registration statement. We may offer the securities under our shelf registration statement from time to time in response to market conditions or other circumstances if we believe such a plan of financing is in our best interests and the best interests of our stockholders.
	Equity Incentive Plans
	Total shares available for the issuance of stock options or other stock-based awards under our stock option and incentive plans were 1,932,432 shares at March 31, 2014.
	Stock Options
	The following table summarizes stock option activity for the three months ended March 31, 2014:
		Number			Weighted-			Weighted-		Aggregate
		of shares			average			average		intrinsic
					exercise price			contractual		value
								term
								(in years)
	Outstanding at December 31, 2013		3,845,370		$	5.75			6.2	$	28,361,438
	Granted		850,550			13.89
	Exercised		(305,848	)		6.2				$	2,824,735
	Forfeited		(29,147	)		9.47
	Expired		—			—
	Outstanding at March 31, 2014		4,360,925		$	7.28			6.7	$	42,547,170
	Vested and expected to vest at March 31, 2014		4,300,598		$	7.25			6.7	$	42,090,718
	Exercisable at March 31, 2014		2,452,611		$	5.48			5	$	28,347,377
	Upon the exercise of stock options, we issue new shares of our common stock. As of March 31, 2014, 192,500 options issued to employees and 50,000 options issued to consultants are unvested, milestone-based options.
	Restricted Stock
	Certain employees, directors and consultants have been awarded restricted stock under our incentive plans. The time-vesting restricted stock grants vest primarily over a period of three years. The following table summarizes restricted share activity for the three months ended March 31, 2014:
		Number of			Weighted average			Aggregate
		shares			grant date			intrinsic
					fair value			value
	Outstanding at December 31, 2013		1,420,930		$	5.27		$	18,401,044
	Granted		386,958			13.91
	Vested		(135,183	)		6.01		$	1,675,558
	Forfeited		(15,791	)		9.59
	Outstanding at March 31, 2014		1,656,914		$	7.19		$	28,233,815
	As of March 31, 2014, 393,000 and 100,000 shares of restricted stock issued to employees and consultants, respectively, are unvested, milestone-based shares.
	On September 14, 2009, we entered in an employment agreement with Ron Bentsur, our Chief Executive Officer, which was amended on January 13, 2012, and further amended on June 11, 2013. The agreement, as amended, terminates on May 20, 2015, subject to certain early termination events. As of March 31, 2014, Mr. Bentsur has been granted a total of 750,000 shares of restricted stock based on the achievement of certain milestone awards described in his employment agreement. In addition, as of March 31, 2014, Mr. Bentsur has the opportunity to earn certain milestone awards as follows:
	(1) 500,000 shares of fully vested common stock will be granted to Mr. Bentsur, upon the first to occur of (a) our first commercial sale of Zerenex in the U.S. off an approved NDA, (b) our receipt of the first royalty upon the commercial sale of Zerenex in the U.S. by a partner to whom we have sold exclusive or non-exclusive commercial rights, or (c) our complete outlicensing of the entire product rights of Zerenex in the U.S.
	(2) 100,000 shares of restricted stock will be granted to Mr. Bentsur upon each event of our outlicensing Zerenex in a foreign market, other than Japan, resulting in a greater than $10 million non-refundable cash payment to us with a gross deal value to us of at least $50 million. Such restricted stock will vest in equal installments over each of the first three anniversaries of the date of grant, provided that Mr. Bentsur remains an employee during such vesting period.
	Stock-Based Compensation
	We incurred $2,552,000 and $581,000 of non-cash compensation expense related to equity incentive grants during the three months ended March 31, 2014 and 2013, respectively. 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 and the expected vesting period. 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.
	Black-Scholes Option Valuation Assumptions	Three months ended March 31,
		2014			2013
	Risk-free interest rates		2	%		0.6	%
	Dividend yield		—			—
	Volatility		104.9	%		102.4	%
	Weighted-average expected term		6.0 years			4.0 years
	The weighted average grant date fair value of options granted for the three months ended March 31, 2014 and 2013 was $11.28 and $2.73 per option, respectively. We used historical information to estimate forfeitures within the valuation model. As of March 31, 2014, there was $10.3 million and $9.9 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 2.6 years and 2.5 years, respectively. These amounts do not include, as of March 31, 2014, 242,500 options outstanding and 493,000 shares of restricted stock outstanding which are milestone-based and vest upon certain corporate milestones, such as FDA approval of our drug candidate and change in control. Stock-based compensation will be measured and recorded if and when it is probable that the milestone will occur.

License_Agreements

License Agreements	3 Months Ended
	Mar. 31, 2014
License Agreements	'
	NOTE 4 - LICENSE AGREEMENTS
	In September 2007, we entered into a Sublicense Agreement with JT and Torii, JT’s pharmaceutical business subsidiary, under which JT and Torii obtained the exclusive sublicense rights for the development and commercialization of ferric citrate in Japan, which is being developed in the U.S. under the trade name Zerenex. 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 (the “Revised 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 2014, JT and Torii received manufacturing and marketing approval of ferric citrate from the Japanese Ministry of Health, Labour and Welfare. Ferric citrate, to be marketed in Japan by JT’s subsidiary, Torii Pharmaceutical Co., Ltd., under the brand name Riona®, is indicated as an oral treatment for the improvement of hyperphosphatemia in patients with CKD. Under the terms of the license agreement with JT and Torii, Keryx received a non-refundable payment of $10.0 million in February 2014 for the achievement of the marketing approval milestone. As a result, we recorded license revenue of $10.0 million in accordance with our revenue recognition policy, which is included in the three months ended March 31, 2014. Keryx will also receive double-digit tiered royalties on net sales of Riona® in Japan, as well as up to an additional $55.0 million upon the achievement of certain annual net sales milestones.

Legal_Proceedings

Legal Proceedings	3 Months Ended
	Mar. 31, 2014
Legal Proceedings	'
	NOTE 5 - LEGAL PROCEEDINGS
	On February 1, 2013, a lawsuit was filed against us and our chief executive officer on behalf of a putative class of all of our shareholders (other than the defendants) who acquired our shares between June 1, 2009 and April 1, 2012. Smith v. Keryx Biopharmaceuticals, Inc., et al., Case No. 1:13-CV-0755-TPG (S.D.N.Y.). On February 26, 2013, a substantially similar lawsuit was filed against us and our chief executive officer as well as our chief financial officer. Park v. Keryx Biopharmaceuticals, Inc., et al., Case No. 1:13-CV-1307-TPG (S.D.N.Y.). On June 10, 2013, the Court entered an Order consolidating the two lawsuits and appointing a lead plaintiff. The case was styled In re Keryx Biopharmaceuticals, Inc. Securities Litigation, Case No. 1:13-CV-0755-KBF (S.D.N.Y.). On July 10, 2013, the lead plaintiff filed a Consolidated Amended Complaint that, in substance, repeated the claims alleged in the consolidated lawsuits. The Consolidated Amended Complaint asserted claims against (i) us for alleged violations of Section 10(b) of the Securities Exchange Act of 1934 (“Exchange Act”) and Rule 10b-5 promulgated thereunder and (ii) our chief executive officer for alleged violations of Sections 10(b) and 20(a) of the Exchange Act and Rule 10b-5. The claims in the Consolidated Amended Complaint were premised on general allegations that we and the individual defendant participated directly or indirectly in the preparation and/or issuance of purportedly false and misleading earnings reports, SEC filings, press releases, and other public statements, which allegedly caused our stock to trade at artificially inflated prices. On August 26, 2013, we filed a motion to dismiss the Consolidated Amended Complaint. On February 14, 2014, the Court entered an Opinion and Order granting the motion to dismiss. The Court entered Judgment for the Defendants on February 24, 2014. The lead plaintiff did not appeal the Judgment and this matter is now concluded.

General_Policies

General (Policies)	3 Months Ended
	Mar. 31, 2014
Basis of Presentation	'
	Basis of Presentation
	We are a biopharmaceutical company focused on focused on bringing innovative therapies to market for patients suffering from renal disease. Most of our biopharmaceutical development and substantially all of our administrative operations during the three months ended March 31, 2014 and 2013 were conducted in the United States of America.
	The accompanying unaudited consolidated financial statements were prepared in accordance with U.S. generally accepted accounting principles (“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 the consolidated financial statements have been included. Nevertheless, these unaudited 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, 2013. The results of operations for the three months ended March 31, 2014, are not necessarily indicative of the results that may be expected for the entire fiscal year or any other interim period.
	Except for 2009, we have incurred substantial operating losses since our inception, and expect to continue to incur operating losses for the foreseeable future and may never become profitable. As of March 31, 2014, we have an accumulated deficit of $452.9 million.
	Our major sources of cash have been proceeds from various public and private offerings of our common stock, option and warrant exercises, interest income, and from the upfront and milestone payments from our Sublicense Agreement with Japan Tobacco Inc. (“JT”) and Torii Pharmaceutical Co., Ltd. (“Torii”) and miscellaneous payments from our other prior licensing activities. We have not yet commercialized any drug candidate and cannot be sure if we will ever be able to do so. Even if we commercialize a drug candidate, we may not become profitable. Our ability to achieve profitability depends on a number of factors, including our ability to complete our development efforts, obtain regulatory approval for our drug candidate, successfully complete any post-approval regulatory obligations and successfully manufacture and commercialize our drug candidate alone or in partnership. We may continue to incur substantial operating losses even if we begin to generate revenues from our drug candidate, if approved.
	We have completed a U.S.-based Phase 3 clinical program for Zerenex for the treatment of hyperphosphatemia (elevated phosphate levels) in patients with chronic kidney disease, or CKD, on dialysis, conducted pursuant to a Special Protocol Assessment, or SPA, agreement with the U.S. Food and Drug Administration, or FDA. Our New Drug Application, or NDA, is currently under review by the FDA with an assigned Prescription Drug User Fee Act, or PDUFA, goal date of June 7, 2014. In addition, in March 2014, we submitted a Marketing Authorization Application, or MAA, with the European Medicines Agency, or EMA, seeking the approval of Zerenex as a treatment for hyperphosphatemia in patients with CKD, including dialysis and non-dialysis dependent CKD, or NDD-CKD. Also in March 2014, the EMA validated our MAA, confirming that the submission is sufficiently complete to begin the formal review process.
	We have also completed a U.S.-based Phase 2 study of Zerenex for the management of elevated serum phosphorus levels and iron deficiency anemia in subjects with Stage 3 to 5 NDD-CKD.
	In January 2014, we raised approximately $107.6 million, net of underwriting discounts and offering expenses of approximately $7.5 million, in an underwritten public offering. We have a shelf registration statement on Form S-3 filed and declared effective by the Securities and Exchange Commission in August 2013, which provides for the offering of up to $150 million of common stock and warrants in the aggregate. Subsequent to the underwritten public offering completed in January 2014, there remains approximately $34.9 million of our common stock and warrants available for sale on this shelf registration statement. See Note 3 for additional information.
	In January 2014, our Japanese partner, JT and Torii, received manufacturing and marketing approval of ferric citrate from the Japanese Ministry of Health, Labour and Welfare. Ferric citrate, to be marketed in Japan by JT’s subsidiary, Torii, under the brand name Riona®, is indicated as an oral treatment for the improvement of hyperphosphatemia in patients with CKD, including dialysis and NDD-CKD. Under the license agreement with JT and Torii, Keryx received a non-refundable payment of $10.0 million in February 2014 for the achievement of the marketing approval milestone. Keryx will also receive double-digit tiered royalties on net sales of Riona® in Japan, as well as up to an additional $55.0 million upon the achievement of certain annual net sales milestones. See Note 4 for additional information.
	We currently expect that our existing capital resources combined with future anticipated cash flows will be sufficient to operate our business plan. The actual amount of cash that we will need to operate is subject to many factors, including, but not limited to, the timing and expenditures associated with the build-up of pre-launch/launch inventory and capacity expansion, the timing and expenditures associated with the respective regulatory review processes for our U.S. NDA and EU MAA filings, the timing and expenditures associated with pre-commercial/commercial activities related to Zerenex, and the timing, design and conduct of clinical trials for Zerenex. We may depend upon significant additional financings to provide the cash necessary to execute our current operations, including the commercialization of Zerenex.
	Our common stock is listed on the NASDAQ Capital Market and trades under the symbol “KERX.”
Cash and Cash Equivalents	'
	Cash and Cash Equivalents
	We treat liquid investments with original maturities of three months or less when purchased as cash and cash equivalents.
Investment Securities	'
	Investment Securities
	We classify our short-term debt securities as held-to-maturity. Held-to-maturity securities are those securities in which we have the ability and intent to hold the security until maturity. Held-to-maturity securities are recorded at amortized cost, adjusted for the amortization or accretion of premiums or discounts. Premiums and discounts are amortized or accreted over the life of the related held-to-maturity security as an adjustment to yield using the effective interest method. Available-for-sale investment securities are recorded at fair value (see Note 2 – Fair Value Measurements). Other-than-temporary impairment charges are included in interest and other income, net, and unrealized gains (losses), if determined to be temporary, are included in accumulated other comprehensive income (loss) in stockholders’ equity.
	The following table summarizes our investment securities at March 31, 2014, and December 31, 2013:
	(in thousands)	March 31, 2014		December 31, 2013
	Short-term investments (held to maturity):
	Obligations of domestic governmental agencies (mature between May 2014 and January 2015)	$	49,665	$	—
	Total short-term investment securities	$	49,665	$	—
Revenue Recognition	'
	Revenue Recognition
	We recognize license revenue in accordance with the revenue recognition guidance of the FASB Accounting Standards Codification (the “Codification”). We analyze each element of our licensing agreement to determine the appropriate revenue recognition. The terms of the license agreement may include payments to us of non-refundable up-front license fees, milestone payments if specified objectives are achieved, and/or royalties on product sales. We recognize revenue from upfront payments over the period of significant involvement under the related agreements unless the fee is in exchange for products delivered or services rendered that represent the culmination of a separate earnings process and no further performance obligation exists under the contract. We recognize milestone payments as revenue upon the achievement of specified milestones only if (1) the milestone payment is non-refundable, (2) substantive effort is involved in achieving the milestone, (3) the amount of the milestone is reasonable in relation to the effort expended or the risk associated with achievement of the milestone, and (4) the milestone is at risk for both parties. If any of these conditions are not met, we defer the milestone payment and recognize it as revenue over the estimated period of performance under the contract.
Stock-Based Compensation	'
	Stock-Based Compensation
	We recognize all share-based payments to employees and to non-employee directors for service on our board of directors as compensation expense in the consolidated financial statements based on the grant date fair values of such payments. Stock-based compensation expense recognized each period is based on the value of the portion of share-based payment awards that is ultimately expected to vest during the period. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.
	For share-based payments to consultants and other third-parties, compensation expense is determined at the “measurement date.” The expense is recognized over the vesting period of the award. Until the measurement date is reached, the total amount of compensation expense remains uncertain. We record compensation expense based on the fair value of the award at the reporting date. The awards to consultants and other third-parties are then revalued, or the total compensation is recalculated based on the then current fair value, at each subsequent reporting date.
Income Taxes	'
	Income Taxes
	As of March 31, 2014, we have U.S. net operating loss carryforwards of approximately $411.1 million which expire from 2019 through 2033. We have established a 100% valuation allowance against our net deferred tax assets due to our history of pre-tax losses and the likelihood that the deferred tax assets will not be realizable. Due to our historical equity transactions, the utilization of certain tax loss carryforwards may be subject to annual limitations imposed by Internal Revenue Code Section 382 relating to the change of control provisions.
	We are not aware of any unrecorded tax liabilities which would impact our financial position or our results of operations.
Net Loss Per Share	'
	Net Loss Per 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 options outstanding as of March 31, 2014 and 2013, which are not included in the computation of net loss per share amounts, were 4,360,925 and 3,882,100, respectively.
Comprehensive Loss	'
	Comprehensive Loss
	Comprehensive loss is the same as net loss for all periods presented.
Segment Reporting	'
	Segment Reporting
	We operate in only one reportable segment: the Products segment.
Impairment of Goodwill	'
	Impairment of Goodwill
	Goodwill is reviewed for impairment annually, or when events arise that could indicate that an impairment exists. We test for goodwill impairment using a two-step process. The first step compares the fair value of the reporting unit with the unit’s carrying value, including goodwill. When the carrying value of the reporting unit is greater than fair value, the unit’s goodwill may be impaired, and the second step must be completed to measure the amount of the goodwill impairment charge, if any. In the second step, the implied fair value of the reporting unit’s goodwill is compared with the carrying amount of the unit’s goodwill. If the carrying amount is greater than the implied fair value, the carrying value of the goodwill must be written down to its implied fair value. As of December 31, 2013, management concluded that there was no impairment of our goodwill. As of March 31, 2014, management determined that there were no impairment indicators that would trigger a goodwill impairment analysis.

General_Tables

General (Tables)	3 Months Ended
	Mar. 31, 2014
Summary of Investment Securities	'
	The following table summarizes our investment securities at March 31, 2014, and December 31, 2013:
	(in thousands)	March 31, 2014		December 31, 2013
	Short-term investments (held to maturity):
	Obligations of domestic governmental agencies (mature between May 2014 and January 2015)	$	49,665	$	—
	Total short-term investment securities	$	49,665	$	—

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
Fair Value Measurements of Financial Assets	'
	The following table provides the fair value measurements of applicable financial assets as of March 31, 2014:
			Financial assets at fair value
			as of March 31, 2014
	(in thousands)		Level 1		Level 2		Level 3
	Money market funds (1)		$	73,755	$	—	$	—
	Obligations of domestic governmental agencies (held-to-maturity) (2)			49,665		—		—
	Total		$	123,420	$	—	$	—
	-1	Included in cash and cash equivalents on our consolidated balance sheet. The carrying amount of money market funds is a reasonable estimate of fair value.
	-2	Amortized cost approximates fair value.

Stockholders_Equity_Tables

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2014
Summary of Stock Option Activity	'
	The following table summarizes stock option activity for the three months ended March 31, 2014:
		Number			Weighted-			Weighted-		Aggregate
		of shares			average			average		intrinsic
					exercise price			contractual		value
								term
								(in years)
	Outstanding at December 31, 2013		3,845,370		$	5.75			6.2	$	28,361,438
	Granted		850,550			13.89
	Exercised		(305,848	)		6.2				$	2,824,735
	Forfeited		(29,147	)		9.47
	Expired		—			—
	Outstanding at March 31, 2014		4,360,925		$	7.28			6.7	$	42,547,170
	Vested and expected to vest at March 31, 2014		4,300,598		$	7.25			6.7	$	42,090,718
	Exercisable at March 31, 2014		2,452,611		$	5.48			5	$	28,347,377
Summary of Restricted Share Activity	'
	The following table summarizes restricted share activity for the three months ended March 31, 2014:
		Number of			Weighted average			Aggregate
		shares			grant date			intrinsic
					fair value			value
	Outstanding at December 31, 2013		1,420,930		$	5.27		$	18,401,044
	Granted		386,958			13.91
	Vested		(135,183	)		6.01		$	1,675,558
	Forfeited		(15,791	)		9.59
	Outstanding at March 31, 2014		1,656,914		$	7.19		$	28,233,815
Black-Scholes Option Valuation Assumptions	'
	Black-Scholes Option Valuation Assumptions	Three months ended March 31,
		2014			2013
	Risk-free interest rates		2	%		0.6	%
	Dividend yield		—			—
	Volatility		104.9	%		102.4	%
	Weighted-average expected term		6.0 years			4.0 years

General_Additional_Information

General - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended
	Feb. 28, 2014	Jan. 22, 2014	Aug. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
				Segment
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]	'	'	'	'	'	'
Accumulated deficit	'	'	'	($452,870,000)	'	($439,340,000)
Proceeds from public offering, net	'	'	'	115,057,000	80,393,000	'
Underwriting discounts and offering expenses	'	'	'	7,460,000	'	'
Shelf registration statements, offering maximum amount of common stock and warrant	'	34,900,000	150,000,000	'	'	'
License agreements, non-refundable milestone payment received	10,000,000	'	'	'	'	'
License agreements, potential milestone receivable	'	'	'	55,000,000	'	'
Net operating loss carryforwards	'	'	'	411,100,000	'	'
Net operating loss carryforwards, valuation allowance percentage	'	'	'	100.00%	'	'
Option outstanding, not included in computation of net loss per share amount	'	'	'	4,360,925	3,882,100	'
Number of reportable segments	'	'	'	1	'	'
Impairment of goodwill	'	'	'	0	'	'
Maximum	'	'	'	'	'	'
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]	'	'	'	'	'	'
Liquid investments, original maturities	'	'	'	'3 months	'	'
Net operating loss carryforwards, expiration period	'	'	'	'2033	'	'
Minimum	'	'	'	'	'	'
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]	'	'	'	'	'	'
Net operating loss carryforwards, expiration period	'	'	'	'2019	'	'
Public offering	'	'	'	'	'	'
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]	'	'	'	'	'	'
Proceeds from public offering, net	'	107,600,000	'	'	'	'
Underwriting discounts and offering expenses	'	$7,500,000	'	'	'	'

Summary_of_Investment_Securiti

Summary of Investment Securities (Detail) (USD $)	Mar. 31, 2014
In Thousands, unless otherwise specified
Investment [Line Items]	'
Obligations of domestic governmental agencies (mature between May 2014 and January 2015)	$49,665
Total short-term investment securities	$49,665

Fair_Value_Measurements_of_Fin

Fair Value Measurements of Financial Assets (Detail) (Level 1, USD $)	Mar. 31, 2014
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'
Financial assets at fair value	$123,420
Money market funds	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'
Financial assets at fair value	73,755	[1]
Obligations of domestic governmental agencies | Held-to-maturity Securities	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'
Financial assets at fair value	$49,665	[2]
[1]	Included in cash and cash equivalents on our consolidated balance sheet. The carrying amount of money market funds is a reasonable estimate of fair value.
[2]	Amortized cost approximates fair value.

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (USD $)

1 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

1 Months Ended

Jan. 22, 2014

Aug. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Jan. 22, 2014

Chief Executive Officer

Scenario 1

Scenario 2

Restricted Stock

Restricted Stock

Restricted Stock

Employee Stock Option

Stock Option

Stock Option

Maximum

Unvested milestone-based employee awards

Unvested milestone based consultant awards

Unvested Milestone-Based Options

Unvested Milestone-Based Options

Milestone-based and vest upon certain corporate milestones

Milestone-based and vest upon certain corporate milestones

Public offering

Chief Executive Officer

Scenario 2

Restricted Stock

Restricted Stock

Employee Stock Option

Non Employee Stock Options

Restricted Stock

Stock Option

Stockholders Equity Note [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock issued during period, shares, new issues

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7,935,000

Share price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$14.50

Proceeds from issuance of common stock, gross

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$115,100,000

Proceeds from issuance of common stock, net

'

'

115,057,000

80,393,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

107,600,000

Underwriting discounts and offering expenses

'

'

7,460,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7,500,000

Shelf registration statements, offering maximum amount of common stock and warrant

34,900,000

150,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares available for the issuance of stock options

'

'

1,932,432

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of options

'

'

'

'

'

'

'

'

'

'

'

4,360,925

3,845,370

'

'

'

192,500

50,000

'

242,500

'

Stock awards vesting period

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

Restricted stock issued

'

'

'

'

'

'

'

1,656,914

1,420,930

'

'

'

'

'

393,000

100,000

'

'

493,000

'

'

Number of shares of restricted stock granted

'

'

'

'

'

'

'

'

'

750,000

'

'

'

'

'

'

'

'

'

'

'

Employment agreement, termination date

'

'

'

'

'2015-05-20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of shares of restricted stock to be granted

'

'

'

'

'

500,000

100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Minimum non-refundable cash payment from outlicensing Zerenex in foreign market other than Japan to trigger granting of 100,000 shares of restricted stock

'

'

'

'

'

'

10,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Gross deal value from outlicensing Zerenex in foreign market other than Japan to trigger granting of 100,000 shares of restricted stock

'

'

'

'

'

'

50,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Non cash compensation expense related to equity incentive granted

'

'

2,552,000

581,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average grant date fair value of options granted

'

'

$11.28

$2.73

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total unrecognized compensation cost related to non-vest stock options

'

'

10,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total unrecognized compensation cost related to restricted stock

'

'

'

'

'

'

'

$9,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average recognition periods for unrecognized compensation cost

'

'

'

'

'

'

'

'2 years 6 months

'

'

'2 years 7 months 6 days

'

'

'

'

'

'

'

'

'

'

Summary_of_Stock_Option_Activi

Summary of Stock Option Activity (Detail) (Stock Option, USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Stock Option	'	'
Number of shares	'	'
Outstanding at beginning of period	3,845,370	'
Granted	850,550	'
Exercised	-305,848	'
Forfeited	-29,147	'
Expired	'	'
Outstanding at end of period	4,360,925	3,845,370
Vested and expected to vest at March 31, 2014	4,300,598	'
Exercisable at March 31, 2014	2,452,611	'
Weighted-average exercise price	'	'
Outstanding at beginning of period	$5.75	'
Granted	$13.89	'
Exercised	$6.20	'
Forfeited	$9.47	'
Expired	'	'
Outstanding at end of period	$7.28	$5.75
Vested and expected to vest at March 31, 2014	$7.25	'
Exercisable at March 31, 2014	$5.48	'
Weighted-average contractual term	'	'
Outstanding	'6 years 8 months 12 days	'6 years 2 months 12 days
Vested and expected to vest at March 31, 2014	'6 years 8 months 12 days	'
Exercisable at March 31, 2014	'5 years	'
Aggregate intrinsic value	'	'
Outstanding at beginning of period	$28,361,438	'
Granted	'	'
Exercised	2,824,735	'
Forfeited	'	'
Expired	'	'
Outstanding at end of period	42,547,170	28,361,438
Vested and expected to vest at March 31, 2014	42,090,718	'
Exercisable at March 31, 2014	$28,347,377	'

Summary_of_Restricted_Share_Ac

Summary of Restricted Share Activity (Detail) (Restricted Stock, USD $)	3 Months Ended
	Mar. 31, 2014
Restricted Stock	'
Number of shares	'
Outstanding at beginning of period	1,420,930
Granted	386,958
Vested	-135,183
Forfeited	-15,791
Outstanding at end of period	1,656,914
Weighted average grant date fair value	'
Outstanding at beginning of period	$5.27
Granted	$13.91
Vested	$6.01
Forfeited	$9.59
Outstanding at end of period	$7.19
Aggregate intrinsic value	'
Outstanding at beginning of period	$18,401,044
Granted	'
Vested	$1,675,558
Forfeited	'
Outstanding at end of period	$28,233,815

Black_Scholes_Option_Valuation

Black Scholes Option Valuation Assumptions (Detail)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Risk-free interest rates	2.00%	0.60%
Dividend yield	'	'
Volatility	104.90%	102.40%
Weighted-average expected term	'6 years	'4 years

License_Agreements_Additional_

License Agreements - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Feb. 28, 2014	Mar. 31, 2014	Mar. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'
License agreements, non-refundable milestone payment received	$10,000,000	'	'
License revenue	'	10,000,000	7,000,000
License agreements, potential milestone receivable	'	$55,000,000	'