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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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.

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No definition available.

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Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

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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.

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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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No definition available.

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Fair value of asset after deduction of liability.

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No definition available.

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

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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The cash outflow associated with the acquisition of a controlling interest in another entity or an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, joint venture or equity method investment).

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair value Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair value measurements
Strategic investments		$ 18,107	$ 2,000
Carrying Value
Fair value measurements
Strategic investments	$ 18,100
Equity investments under cost method		20,100	2,000
Long-term debt		155,800	156,800
Level 2 \| Estimated Fair Value
Fair value measurements
Long-term debt		159,200	159,900
Recurring basis
Fair value measurements
Total assets and liabilities measured at fair value		60,367
Total assets measured at fair value			68,636
Recurring basis \| Interest rate swap
Fair value measurements
Derivative liabilities		52
Recurring basis \| Certificate of deposit
Fair value measurements
Cash and cash equivalents		391	391
Recurring basis \| Money market funds
Fair value measurements
Cash and cash equivalents		2,894	29,027
Recurring basis \| Short Term Investments
Fair value measurements
Investments		7,076	9,237
Recurring basis \| Commercial paper
Fair value measurements
Cash and cash equivalents		49,954	29,981
Recurring basis \| Level 1
Fair value measurements
Total assets and liabilities measured at fair value		3,449
Total assets measured at fair value			30,778
Recurring basis \| Level 1 \| Money market funds
Fair value measurements
Cash and cash equivalents		2,894	29,027
Recurring basis \| Level 1 \| Short Term Investments
Fair value measurements
Investments		555	1,751
Recurring basis \| Level 2
Fair value measurements
Total assets and liabilities measured at fair value		56,918
Total assets measured at fair value			37,858
Recurring basis \| Level 2 \| Interest rate swap
Fair value measurements
Derivative liabilities		52
Recurring basis \| Level 2 \| Certificate of deposit
Fair value measurements
Cash and cash equivalents		391	391
Recurring basis \| Level 2 \| Money market funds
Fair value measurements
Cash and cash equivalents			29,981
Recurring basis \| Level 2 \| Short Term Investments
Fair value measurements
Investments		6,521	$ 7,486
Recurring basis \| Level 2 \| Commercial paper
Fair value measurements
Cash and cash equivalents		$ 49,954