Financial Instruments - Summary of Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	$ 55,371	$ 61,985
Available-for-sale securities, Gross Unrealized Gains	11	7
Available-for-sale securities, Gross Unrealized Losses	(123)	(156)
Estimated Fair Values	55,259	61,836
Corporate Bonds And Notes
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	43,517	36,590
Available-for-sale securities, Gross Unrealized Gains	11	7
Available-for-sale securities, Gross Unrealized Losses	(83)	(95)
Estimated Fair Values	43,445	36,502
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	3,733	5,220
Available-for-sale securities, Gross Unrealized Gains	0	0
Available-for-sale securities, Gross Unrealized Losses	(2)	(4)
Estimated Fair Values	3,731	5,216
Treasury And Agency Notes And Bills
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	6,000	6,029
Available-for-sale securities, Gross Unrealized Gains	0	0
Available-for-sale securities, Gross Unrealized Losses	(38)	(57)
Estimated Fair Values	5,962	5,972
Money Market Funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	2,121	14,146
Available-for-sale securities, Gross Unrealized Gains	0	0
Available-for-sale securities, Gross Unrealized Losses	0	0
Estimated Fair Values	2,121	14,146
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Values	2,121	14,457
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Values	$ 53,138	$ 47,379

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 5
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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