Summary of Significant Accounting Policies - Schedule of Financial Assets That Have Been Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial assets
Total	$ 200,325	$ 192,982
Current [Member] \| Corporate Debt Securities [Member]
Financial assets
Investments	86,447	10,135
Current [Member] \| Commercial Paper [Member]
Financial assets
Investments	29,828	29,980
Current [Member] \| US Government and Agency Securities [Member]
Financial assets
Investments	1,000
Current [Member] \| Certificates of Deposit [Member]
Financial assets
Investments		15,000
Non-current [Member] \| US Government and Agency Securities [Member]
Financial assets
Investments		3,545
Non-current [Member] \| Corporate Debt Securities (One to Two Year Maturity) [Member]
Financial assets
Investments	33,878	5,113
Money Market Funds [Member]
Financial assets
Cash equivalents	49,172	129,209
Level 1 [Member]
Financial assets
Total	49,172	129,209
Level 1 [Member] \| Money Market Funds [Member]
Financial assets
Cash equivalents	49,172	129,209
Level 2 [Member]
Financial assets
Total	151,153	63,773
Level 2 [Member] \| Current [Member] \| Corporate Debt Securities [Member]
Financial assets
Investments	86,447	10,135
Level 2 [Member] \| Current [Member] \| Commercial Paper [Member]
Financial assets
Investments	29,828	29,980
Level 2 [Member] \| Current [Member] \| US Government and Agency Securities [Member]
Financial assets
Investments	1,000
Level 2 [Member] \| Current [Member] \| Certificates of Deposit [Member]
Financial assets
Investments		15,000
Level 2 [Member] \| Non-current [Member] \| US Government and Agency Securities [Member]
Financial assets
Investments		3,545
Level 2 [Member] \| Non-current [Member] \| Corporate Debt Securities (One to Two Year Maturity) [Member]
Financial assets
Investments	$ 33,878	$ 5,113

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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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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- References

No definition available.

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Available-for-Sale Securities
-URI http://asc.fasb.org/extlink&oid=6505594

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 1
-Subparagraph a, f, g
-Article 7

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