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

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value portion of contractual obligation to pay money on demand or on fixed or determinable dates.

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FAIR VALUE - Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Fair value measurements
Cash and cash equivalents	$ 39,206	$ 48,921	$ 52,151	$ 41,135
Marketable securities	235,464	262,179
Fair Value
Fair value measurements
Total	274,670	311,100
Fair Value Inputs Level 1
Fair value measurements
Total	30,706	48,921
Fair Value Inputs Level 2
Fair value measurements
Total	243,964	262,179
Long-term debt	4,600	4,700
Cash and Money Market \| Fair Value
Fair value measurements
Cash and cash equivalents	30,706	48,921
Cash and Money Market \| Fair Value Inputs Level 1
Fair value measurements
Cash and cash equivalents	30,706	48,921
Corporate bonds \| Fair Value
Fair value measurements
Marketable securities	110,397	136,937
Corporate bonds \| Fair Value Inputs Level 2
Fair value measurements
Marketable securities	110,397	136,937
U.S. government agency securities \| Fair Value
Fair value measurements
Cash and cash equivalents	3,000
Marketable securities	49,463	49,474
U.S. government agency securities \| Fair Value Inputs Level 2
Fair value measurements
Cash and cash equivalents	3,000
Marketable securities	49,463	49,474
Asset backed securities \| Fair Value
Fair value measurements
Marketable securities	54,241	55,640
Asset backed securities \| Fair Value Inputs Level 2
Fair value measurements
Marketable securities	54,241	55,640
Commercial paper. \| Fair Value
Fair value measurements
Cash and cash equivalents	4,700
Marketable securities	17,110	19,076
Commercial paper. \| Fair Value Inputs Level 2
Fair value measurements
Cash and cash equivalents	4,700
Marketable securities	17,110	19,076
Certificates of deposit \| Fair Value
Fair value measurements
Cash and cash equivalents	800
Marketable securities	4,253	1,052
Certificates of deposit \| Fair Value Inputs Level 2
Fair value measurements
Cash and cash equivalents	800
Marketable securities	$ 4,253	$ 1,052