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Cash, Cash Equivalents and Investments - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Cash and Cash Equivalents [Abstract] |  |  |
Cash balance included foreign bank balance | $ 67,502,000 | $ 66,777,000 |
Gross realized gains on sale of debt securities | 669,000 | 929,000 | $ 292,000
Gross realized losses on sale of debt securities | $ 168,000 | $ 100,000 | $ 101,000

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- Definition Due from foreign banks. + References No definition available. + Details
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Balance Type: | debit
Period Type: | instant

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | credit
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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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