Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Net operating loss carryforwards	$ 79,050,000	$ 66,209,000
Research and development credit carryforwards	26,112,000	25,058,000
Net Operating loss Carryforwards resulting from excess tax deduction	4,400,000
Increase (decrease) in valuation allowance	10,000,000
Net Operating Loss Carryforwards
Income Taxes [Line Items]
Increase (decrease) in deferred tax assets	(11,200,000)
General Business Credits
Income Taxes [Line Items]
Increase (decrease) in deferred tax assets	(636,000)
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	206,900,000
Net operating loss carryforwards, expiration date	2033
Research and Development Credit
Income Taxes [Line Items]
Net operating loss carryforwards, expiration date	2033
Research and development credit carryforwards	$ 26,000,000