Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Loss Carryforwards [Line Items]
Cumulative change in ownership	More than 50% occurs within a three-year period
Percentage of cumulative change in ownership	50.00%
Deferred tax assets for net operating losses	$ 82,753,000	$ 76,152,000
Tax credits	19,903,000	18,405,000
Accrual for interest or penalties	0	0
Interest or penalties expense	0	0	0
Valuation allowance	119,801,000	106,727,000
Net operating loss carryforwards related to windfall tax benefits	1,600,000
Research development and investment credit [Member]
Operating Loss Carryforwards [Line Items]
Federal research and development credit and orphan drug credit carryforwards	8,800,000	8,600,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	101,200,000
Research and development credits and other tax credits	12,200,000
Net operating loss carryforwards	301,000,000	285,500,000
Federal research and development credit and orphan drug credit carryforwards	26,300,000	25,300,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	17,200,000
Net operating loss carryforwards	$ 282,200,000	$ 261,300,000