Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		$ 192,602,000
Cash, cash equivalents and short-term investments, Gross unrealized losses		(111,000)
Cash, cash equivalents and short-term investments, Fair market value	$ 0	192,491,000
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		75,304,000
Cash, cash equivalents and short-term investments, Fair market value		75,304,000
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		48,936,000
Cash, cash equivalents and short-term investments, Gross unrealized losses		(37,000)
Cash, cash equivalents and short-term investments, Fair market value		48,899,000
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		50,966,000
Cash, cash equivalents and short-term investments, Gross unrealized losses		(48,000)
Cash, cash equivalents and short-term investments, Fair market value		50,918,000
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		17,396,000
Cash, cash equivalents and short-term investments, Gross unrealized losses		(26,000)
Cash, cash equivalents and short-term investments, Fair market value		17,370,000
Cash and Cash Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		80,304,000
Cash, cash equivalents and short-term investments, Fair market value		80,304,000
Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Cash, cash equivalents and short-term investments, Amortized cost		112,298,000
Cash, cash equivalents and short-term investments, Gross unrealized losses		(111,000)
Cash, cash equivalents and short-term investments, Fair market value		$ 112,187,000

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

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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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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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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