Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes [Line Items]
Deferred tax liability associated with the issuance of the convertible notes									$ 22,700,000
Net operating loss carry forwards	44,100,000								44,100,000
Net loss	(28,034,000)	(39,701,000)	(16,379,000)	(34,198,000)	(30,856,000)	(27,392,000)	(30,249,000)	(13,530,000)	(118,312,000)	(102,027,000)	(73,109,000)
Annual limitation on net operating loss	77,300,000								77,300,000
Deferred tax asset attributable to excess stock option deductions									7,200,000
Valuation allowance	227,821,000				181,521,000				227,821,000	181,521,000
Deferred tax assets, increase in valuation allowance									46,300,000
Unrecognized tax benefit liability	2,700,000				2,700,000				2,700,000	2,700,000	10,261,000	10,011,000
Maximum
Income Taxes [Line Items]
State income tax returns examination period, years									5
Minimum
Income Taxes [Line Items]
State income tax returns examination period, years									3
State Tax Audit
Income Taxes [Line Items]
Reduction in a liability for unrecognized tax benefit								3,600,000
State Matters
Income Taxes [Line Items]
Reduction in a liability for unrecognized tax benefit								500,000
Federal
Income Taxes [Line Items]
Net operating loss carry forwards	350,800,000								350,800,000
Tax credit carryforwards	51,600,000								51,600,000
State
Income Taxes [Line Items]
Net operating loss carry forwards	$ 404,500,000								$ 404,500,000