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Cash Equivalents, Restricted Cash and Short-Term Investments Classified as Available-for-sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 76,831	$ 119,057
Gross Unrealized Gains	34	2
Gross Unrealized Losses		(6)
Estimated Fair Value	76,865	119,053
Restricted cash
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		50
Estimated Fair Value		50
Federal Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,995	14,774
Gross Unrealized Gains	11	1
Estimated Fair Value	10,006	14,775
Federal Agency Securities | Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		999
Estimated Fair Value		999
Money Market Funds | Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	15,369	29,090
Estimated Fair Value	15,369	29,090
U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	51,467	74,144
Gross Unrealized Gains	23	1
Gross Unrealized Losses		(6)
Estimated Fair Value	51,490	74,139
Cash and Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	15,369	30,089
Short-Term Investments
Schedule Of Available For Sale Securities [Line Items]
Estimated Fair Value	$ 61,496	$ 88,914

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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