Amount of current and deferred federal income tax expense (benefit) attributable to income (loss) from continuing operations.

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Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Provision for federal income taxes	$ 0	$ 0	$ 0
Increase in valuation allowance	12,700,000	9,100,000
Unrecognized tax benefits	332,000us-gaap_UnrecognizedTaxBenefits	287,000us-gaap_UnrecognizedTaxBenefits	73,000us-gaap_UnrecognizedTaxBenefits	62,000us-gaap_UnrecognizedTaxBenefits
Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	85,700,000
Federal [Member] \| Research and Development Tax Credits [Member]
Income Tax Contingency [Line Items]
Tax credits	840,000
Tax credit, expiration	Begin to expire in 2029
Federal [Member] \| Orphan Drug Credit [Member]
Income Tax Contingency [Line Items]
Tax credits	1,800,000
Tax credit, expiration	Begins to expire in 2033
State [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards	55,100,000
Operating loss carryforwards, expiration	Begin to expire in 2029
State [Member] \| Research and Development Tax Credits [Member]
Income Tax Contingency [Line Items]
Tax credits	$ 698,000