Income Taxes - Additional Information (Detail) (USD $)			12 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 Federal Tax	Sep. 30, 2013 Minimum	Sep. 30, 2013 Maximum
Income Taxes [Line Items]
Deferred tax asset, exercise of stock options		$ 1,800,000
Deferred tax assets valuation allowance		204,300,000
Unrecognized tax benefits or liabilities	0	0
Accrued interest or penalties related to uncertain tax positions		0
Federal tax net operating loss carryforward			277,700,000
Federal research and experimentation and orphan drug credit carryforward			53,300,000
Restricted NOLs			67,200,000
Federal tax credits			$ 4,800,000
Tax years open to examination by major taxing jurisdictions				1998	2012