Fair Value Measurements - Estimated Value of Cash Equivalents and Marketable Securities and Gross Unrealized Holding Gains and Losses (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Cash Equivalents and Marketable Securities [Line Items]
Cash equivalents, Amortized cost	$ 11,837
Cash equivalents, Estimated Fair Value	11,837
Corporate Debt Securities [Member]
Cash Equivalents and Marketable Securities [Line Items]
Cash equivalents, Amortized cost	2,180
Cash equivalents, Estimated Fair Value	2,180
Money Market Funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Cash equivalents, Amortized cost	9,657
Cash equivalents, Estimated Fair Value	9,657
Marketable Securities [Member]
Cash Equivalents and Marketable Securities [Line Items]
Marketable securities, Amortized cost	32,195
Marketable securities, Unrealized gain	3
Marketable securities, Unrealized loss	(18)
Marketable securities, Estimated Fair Value	32,180
Marketable Securities [Member] \| Corporate Debt Securities [Member]
Cash Equivalents and Marketable Securities [Line Items]
Marketable securities, Amortized cost	9,294
Marketable securities, Unrealized loss	(5)
Marketable securities, Estimated Fair Value	9,289
Marketable Securities [Member] \| Commercial Paper [Member]
Cash Equivalents and Marketable Securities [Line Items]
Marketable securities, Amortized cost	22,901
Marketable securities, Unrealized gain	3
Marketable securities, Unrealized loss	(13)
Marketable securities, Estimated Fair Value	$ 22,891

Cash equivalents amortized cost.

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- Definition

Cash equivalents and marketable securities.

+ References

No definition available.

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- Definition

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

+ References

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
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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- Definition

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://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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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity 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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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ 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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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

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