Income Taxes - Reconciliation between the Benefit (Provision) for Income Taxes at Statutory Rate and Effective Tax Rate (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
Sale of IP rights to foreign subsidiary	0.00%	(13.80%)	22.50%
Benefit from foreign losses	0.00%	0.00%	7.80%
Foreign withholding	(0.20%)	(1.20%)	0.50%
Stock compensation expense	(2.00%)	(6.60%)	5.80%
Meals & entertainment	0.00%	0.00%	0.10%
Foreign rate differential	(17.00%)	(1.20%)	(24.00%)
Prior year true-up items	(0.10%)	(0.30%)	1.70%
Tax reserves	(0.10%)	1.80%	3.90%
Loss on foreign share transfer	0.00%	0.00%	5.90%
Credits	0.40%	1.60%	(35.50%)
State Refunds	0.00%	3.80%	0.00%
Other	0.00%	(1.60%)	3.90%
2017 Tax Act impact - federal rate change	(28.70%)	0.00%	0.00%
Valuation allowance	11.60%	(193.40%)	8.20%
Effective tax rate	(1.10%)	(175.90%)	35.80%

Effective Income Tax Rate Reconciliation, Benefit From Foreign Losses

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Effective Income Tax Rate Reconciliation, Foreign Sale Of Intangible Assets, Related Party

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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 Foreign Withholding which can be suitable for both positive as well as negative value.

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Effective Income Tax Rate Reconciliation, Loss On Foreign Share Transfer

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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 Tax Reserves which can be suitable for both positive as well as negative value.

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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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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 statutory income tax expense (benefit) outside of the country of domicile.

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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 revisions of previously reported income tax expense.

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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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