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Reconciliation of Income Tax Expense on Pretax Income at Statutory Rate and Income Tax Expense (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Reconciliation Of Income Taxes [Line Items] |  |  |
Differences between Cayman and foreign statutory tax rates | $ 5,286 | $ 846 | $ 12,509
Permanent differences | 1,441 | 4,109 | (703)
Temporary differences | (129) | 638 | (159)
Alternative minimum tax | 1 | 1 | 9
Income tax on undistributed earnings | 1,196 | 575 | 408
Net changes in income tax credit | 20 | 3,917 | 116
Net changes in valuation allowance of deferred income tax assets | 2,439 | (1,820) | 1,243
Net operating loss carryforwards | (1,180) | (294) | (1,431)
Liabilities related to unrealized tax benefits | (3,066) | (171) | (302)
Adjustment of prior years' taxes and others | (196) | (125) | 101
Income tax expense | 5,812 | 7,676 | 11,791
Cayman Islands Tax Information Authority [Member] |  |  |
Reconciliation Of Income Taxes [Line Items] |  |  |
Tax expense at statutory rate |  |  |

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