Income Taxes - Reconciliation of Statutory Effective Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax benefit at federal statutory rate	35.00%	35.00%
State income tax benefit, net of federal benefit	2.00%	54.40%
Nondeductible executive compensation	(5.60%)	(5.20%)
Tax Cuts and Jobs Act of 2017	(55.60%)	0.00%
Change in valuation allowances	42.60%	(72.20%)
Discrete adjustments for stock based compensation	(3.70%)	(0.00%)
General business credit	2.50%	19.60%
Federal return to provision	(0.00%)	(6.10%)
Other	(3.20%)	(27.70%)
Net income tax benefit (expense)	14.00%	(2.20%)

Effective Income Tax Rate Reconciliation, Nondeductible Executive Compensation, Percent

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Effective income tax rate reconciliation tax adjustments settlements and unusual provisions.

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
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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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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 applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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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 tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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