Income Taxes - Reconciliation of Federal Statutory Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefit	3.45%	3.45%	3.45%
Permanent differences-derivative loss (gain)	(9.10%)	0.11%	110.51%
Permanent differences-other	2.24%	(1.07%)	44.12%
Research and development ("R&D") credit	2.73%	4.91%	(129.12%)
Other	0.61%	0.64%	(30.89%)
Decrease in valuation allowance	(33.93%)	(42.04%)	(24.82%)
Federal statutory income tax rate, Total	0.00%	0.00%	7.25%

Effective income tax rate reconciliation permanent differences.

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Effective income tax rate reconciliation permanent differences other.

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

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage 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 changes in the valuation allowance for deferred tax assets.

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