Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	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	$ 120,798,000	$ 124,903,000
Percentage of cumulative change in ownership	50.00%
Deferred tax assets for net operating losses	$ 83,143,000	85,510,000
Tax credits	19,903,000	19,903,000
Accrual for interest or penalties	0	0
Interest or penalties expense	0	0	$ 0
Valuation allowance	120,798,000	124,903,000
Net operating loss carryforwards related to windfall tax benefits	1,600,000
Gross unrecognized tax benefits	$ 4,340,000	582,000	$ 0	$ 0
Tax year open to examination	1997
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	311,300,000	307,300,000
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	2035
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	$ 262,800,000	275,000,000
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	2016
State and Local Jurisdiction [Member] | Latest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration year	2035