DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	3 Months Ended		1 Months Ended
	Mar. 31, 2015 ReportingUnit Segment	Mar. 31, 2014	Jul. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract]
Minimum age of children for management of nephropathic cystinosis	6 years
Period of orphan drug exclusivity for PROCYSBI in U.S.	7 years
Period of orphan drug exclusivity for PROCYSBI in EU	10 years
Segment Information [Abstract]
Number of segment	1
Cash and Cash Equivalents [Abstract]
Maximum maturity period for investments considered as highly liquid investments	3 months
Cash and cash equivalents	$ 134,537,000	$ 68,075,000		$ 149,613,000	$ 83,052,000
Cash and cash equivalents held by foreign subsidiaries	10,600,000
Fixed Assets [Abstract]
Useful life of significant additions and improvements in fixed assets for capitalization, minimum	1 year
Goodwill and Intangible Assets [Abstract]
Estimated useful life of intangible assets	20 years
Number of reporting unit	1
Convertible Notes [Abstract]
Maturity date	Aug. 01, 2019
Employee Stock Purchase Plan [Abstract]
Employee stock purchase plan maximum shares issued in shares)	1,000,000
Common stock purchase price percentage on fair value (in hundredths)	85.00%
Income taxes [Abstract]
Accrued interest or penalties related to uncertain tax positions	$ 0
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	13,640,271	9,919,147
Officers and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	9,663,956	9,584,383
Convertible Debt [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	3,428,571	0
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	334,764	334,764
Restricted Stock Awards Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potentially dilutive securities (in shares)	212,980	0
Loan Agreement with HC Royalty [Member]
Note Payable [Abstract]
Annual fixed interest rate (in hundredths)			8.00%
Convertible Notes [Abstract]
Maturity date			Jun. 30, 2015