Revenue Recognition - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended			9 Months Ended
	Sep. 03, 2014	Jan. 30, 2014	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue recognized							$ 2,115,000
Non-refundable up-front payment							2,000,000
Payment to be received upon signing of agreement							126,000
Revenue recognized under revenue recognition, up front payment						$ 2,000,000
Royalty and other revenue					$ 126,000			$ 2,117,000
Technology Transfer
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue recognized						$ 0
Estimated selling price				$ 300,000			300,000
Consideration allocated to transaction				11,000			11,000
Royalty and other revenue			$ 126,000
Clinical Development
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Milestone Payment							60,000,000
Potential milestone payments to be received				60,000,000			60,000,000
Initial Commercial Sales
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Potential milestone payments to be received				100,000,000			100,000,000
BioMarin Pharmaceutical, Inc. | Asset Purchase Agreement
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Upfront payment received under purchase agreement		$ 2,000,000
Potential milestone payments to be received				160,000,000			160,000,000
Provision for refund							0
Revenue recognized				$ 0			$ 0	$ 2,100,000
BioMarin Pharmaceutical, Inc. | Clinical Development | Asset Purchase Agreement
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Percentage relate to clinical development from Milestone payment							37.00%
BioMarin Pharmaceutical, Inc. | Initial Commercial Sales | Asset Purchase Agreement
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Percentage relate to clinical development from Milestone payment							63.00%
BioMarin Pharmaceutical, Inc. | Technology Transfer Payments | Asset Purchase Agreement
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Milestone Payment	$ 126,000