Fair Value of Financial Instruments - Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial Assets
Marketable securities available-for-sale	$ 522	$ 51,009
Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	21,834	18,903
Marketable securities available-for-sale	522	51,009
Financial Assets Total	22,356	69,912
Financial Liabilities
Fair value of early conversion feature of convertible debt		82
Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	21,834	3
Marketable securities available-for-sale	0	3,722
Financial Assets Total	21,834	3,725
Financial Liabilities
Fair value of early conversion feature of convertible debt		0
Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	0	18,900
Marketable securities available-for-sale	522	47,287
Financial Assets Total	522	66,187
Financial Liabilities
Fair value of early conversion feature of convertible debt		0
Level 3 \| Fair Value, Measurements, Recurring
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		82
Corporate bonds
Financial Assets
Marketable securities available-for-sale	$ 522	25,657
Corporate bonds \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		25,657
Corporate bonds \| Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Corporate bonds \| Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		25,657
Corporate bonds \| Level 3 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Asset-backed securities
Financial Assets
Marketable securities available-for-sale		12,393
Asset-backed securities \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		12,393
Asset-backed securities \| Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Asset-backed securities \| Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		12,393
Asset-backed securities \| Level 3 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Mortgage-backed securities
Financial Assets
Marketable securities available-for-sale		4,779
Mortgage-backed securities \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		4,779
Mortgage-backed securities \| Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Mortgage-backed securities \| Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		4,779
Mortgage-backed securities \| Level 3 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Government and agency securities
Financial Assets
Marketable securities available-for-sale		5,712
Government and agency securities \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		5,712
Government and agency securities \| Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		3,722
Government and agency securities \| Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		1,990
Government and agency securities \| Level 3 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Municipal bonds
Financial Assets
Marketable securities available-for-sale		2,468
Municipal bonds \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		2,468
Municipal bonds \| Level 1 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		0
Municipal bonds \| Level 2 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		2,468
Municipal bonds \| Level 3 \| Fair Value, Measurements, Recurring
Financial Assets
Marketable securities available-for-sale		$ 0

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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
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-URI http://asc.fasb.org/extlink&oid=6506951

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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

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