Income Taxes - Reconciliation Between Provision for Income Taxes and Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Computed "expected" tax benefit	$ (5,607)	$ (10,621)	$ (7,712)
State income taxes, net of federal benefit	(444)	(1,947)	451
Tax effect of:
Change in valuation allowance	5,102	13,074	(37,179)
Expiration of prior year credits and net operating losses	675	(237)	45,382
Research and development and other tax credits carryovers	0	(672)	(1,097)
Stock compensation	274	337	358
Other	0	66	(203)
Provision for income taxes	$ 0us-gaap_IncomeTaxExpenseBenefit	$ 0us-gaap_IncomeTaxExpenseBenefit	$ 0us-gaap_IncomeTaxExpenseBenefit

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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Income tax reconciliation expiration of prior year credits and net operating losses.

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