Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Cumulative change in ownership	More than 50% occurs within a three-year period
Deferred tax assets	$ 124,903,000	$ 119,801,000
Percentage of cumulative change in ownership	50.00%
Deferred tax assets for net operating losses	85,510,000	82,753,000
Tax credits	19,903,000	19,903,000
Accrual for interest or penalties	0	0
Interest or penalties expense	0	0	0
Tax year open to examination	1997
Valuation allowance	124,903,000	119,801,000
Net operating loss carryforwards related to windfall tax benefits	1,600,000
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	307,300,000	300,800,000
Federal research and development credit and orphan drug credit carryforwards	26,300,000	26,300,000
Domestic Tax Authority [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration year	2018
Federal research and development credit and orphan drug credit carryforwards, expiration year	2018
Domestic Tax Authority [Member] | Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration year	2034
Federal research and development credit and orphan drug credit carryforwards, expiration year	2033
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	275,000,000	282,100,000
Federal research and development credit and orphan drug credit carryforwards	$ 8,800,000	$ 8,800,000
State and Local Jurisdiction [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration year	2015
State and Local Jurisdiction [Member] | Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration year	2034