Cash, Cash Equivalents and Investments - Additional Information (Detail) - USD ($)	12 Months Ended
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

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration