CASH EQUIVALENTS AND INVESTMENTS - Schedule of Activity for Short-Term Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Cash equivalents, amortized cost	$ 1,254	$ 6,619
Cash equivalents, fair value	1,254	6,619
Marketable securities, amortized cost	17,274	61,880
Marketable securities, unrealized gains	0	7
Marketable securities, unrealized losses	(50)	(51)
Marketable securities, fair value	17,224	61,836
Investments, amortized cost	9,083	32,451
Investments, unrealized gains	0	3
Investments, unrealized losses	(52)	(83)
Investments, fair value	$ 9,031	32,371
Minimum
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Period considered to classify available-for-sale securities as investments	1 year
Maximum
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Period considered to classify available-for-sale securities as investments	2 years
Municipal obligations
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost		3,264
Marketable securities, unrealized gains		0
Marketable securities, unrealized losses		(3)
Marketable securities, fair value		3,261
U.S. government agency notes
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	$ 4,091	16,477
Marketable securities, unrealized gains	0	3
Marketable securities, unrealized losses	(19)	(3)
Marketable securities, fair value	4,072	16,477
Investments, amortized cost	3,992	19,473
Investments, unrealized gains	0	3
Investments, unrealized losses	(28)	(39)
Investments, fair value	3,964	19,437
Corporate debt securities
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	8,048	41,893
Marketable securities, unrealized gains	0	4
Marketable securities, unrealized losses	(31)	(45)
Marketable securities, fair value	8,017	41,852
Investments, amortized cost	3,908	10,520
Investments, unrealized gains	0	0
Investments, unrealized losses	(24)	(44)
Investments, fair value	3,884	10,476
Certificates of deposit
Amortized cost, gross unrealized gains and losses and fair value of marketable debt and equity securities and investments
Marketable securities, amortized cost	5,135	246
Marketable securities, unrealized gains	0	0
Marketable securities, unrealized losses	0	0
Marketable securities, fair value	5,135	246
Investments, amortized cost	1,183	2,458
Investments, unrealized gains	0	0
Investments, unrealized losses	0	0
Investments, fair value	$ 1,183	$ 2,458

Represents the period considered to classify available-for-sale debt securities as investments.

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Represents the amortized cost of cash equivalents.

+ References

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This item represents the cost of debt and equity securities, which are categorized as long-term investments, 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.

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This item represents the gross unrealized gains for securities, at a point in time, which are categorized as long-term investments.

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This item represents the gross unrealized losses for securities, at a point in time, which are categorized as long-term investments.

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This item represents the cost of debt and equity securities, which are categorized as marketable securities, 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.

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This item represents the gross unrealized gains for securities, at a point in time, which are categorized as marketable securities.

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- Definition

Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ 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 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

+ 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 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of investments in debt and equity securities, including, but not limited to, held-to-maturity, trading and available-for-sale expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-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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