Fair Value of Financial Instruments - Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financial Assets
Marketable securities available-for-sale	$ 27,771	$ 51,009
Corporate bonds
Financial Assets
Marketable securities available-for-sale	16,407	25,657
Asset-backed securities
Financial Assets
Marketable securities available-for-sale	4,855	12,393
Government and agency securities
Financial Assets
Marketable securities available-for-sale	3,522	5,712
Mortgage-backed securities
Financial Assets
Marketable securities available-for-sale	2,196	4,779
Municipal bonds
Financial Assets
Marketable securities available-for-sale	791	2,468
Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	4,689	18,903
Marketable securities available-for-sale	27,771	51,009
Financial Assets Total	32,460	69,912
Financial Liabilities
Fair value of early conversion feature of convertible debt	0	82
Fair Value, Measurements, Recurring \| Corporate bonds
Financial Assets
Marketable securities available-for-sale	16,407	25,657
Fair Value, Measurements, Recurring \| Asset-backed securities
Financial Assets
Marketable securities available-for-sale	4,855	12,393
Fair Value, Measurements, Recurring \| Government and agency securities
Financial Assets
Marketable securities available-for-sale	3,522	5,712
Fair Value, Measurements, Recurring \| Mortgage-backed securities
Financial Assets
Marketable securities available-for-sale	2,196	4,779
Fair Value, Measurements, Recurring \| Municipal bonds
Financial Assets
Marketable securities available-for-sale	791	2,468
Fair Value, Measurements, Recurring \| Level 1
Financial Assets
Cash equivalents	0	3
Marketable securities available-for-sale	2,477	3,722
Financial Assets Total	2,477	3,725
Financial Liabilities
Fair value of early conversion feature of convertible debt	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Corporate bonds
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Asset-backed securities
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Government and agency securities
Financial Assets
Marketable securities available-for-sale	2,477	3,722
Fair Value, Measurements, Recurring \| Level 1 \| Mortgage-backed securities
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Municipal bonds
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 2
Financial Assets
Cash equivalents	4,689	18,900
Marketable securities available-for-sale	25,294	47,287
Financial Assets Total	29,983	66,187
Financial Liabilities
Fair value of early conversion feature of convertible debt	0	0
Fair Value, Measurements, Recurring \| Level 2 \| Corporate bonds
Financial Assets
Marketable securities available-for-sale	16,407	25,657
Fair Value, Measurements, Recurring \| Level 2 \| Asset-backed securities
Financial Assets
Marketable securities available-for-sale	4,855	12,393
Fair Value, Measurements, Recurring \| Level 2 \| Government and agency securities
Financial Assets
Marketable securities available-for-sale	1,045	1,990
Fair Value, Measurements, Recurring \| Level 2 \| Mortgage-backed securities
Financial Assets
Marketable securities available-for-sale	2,196	4,779
Fair Value, Measurements, Recurring \| Level 2 \| Municipal bonds
Financial Assets
Marketable securities available-for-sale	791	2,468
Fair Value, Measurements, Recurring \| Level 3
Financial Assets
Cash equivalents	0	0
Marketable securities available-for-sale	0	0
Financial Assets Total	0	0
Financial Liabilities
Fair value of early conversion feature of convertible debt	0	82
Fair Value, Measurements, Recurring \| Level 3 \| Corporate bonds
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Asset-backed securities
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Government and agency securities
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Mortgage-backed securities
Financial Assets
Marketable securities available-for-sale	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Municipal bonds
Financial Assets
Marketable securities available-for-sale	$ 0	$ 0

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

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-Publisher FASB
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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
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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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