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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FAIR VALUE (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Fair value measurements
Cash and cash equivalents	$ 40,679,000	$ 58,131,000	$ 17,806,000	$ 12,851,000
Marketable securities	204,472,000us-gaap_AvailableForSaleSecurities	224,625,000us-gaap_AvailableForSaleSecurities
Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Total	245,151,000	282,756,000
Fair Value Inputs Level1 [Member]
Fair value measurements
Total	40,679,000	53,569,000
Fair Value Inputs Level2 [Member]
Fair value measurements
Total	204,472,000	229,187,000
Long-term debt	1,000,000
Cash and Money Market [Member] \| Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Cash and cash equivalents	40,679,000	53,569,000
Cash and Money Market [Member] \| Fair Value Inputs Level1 [Member]
Fair value measurements
Cash and cash equivalents	40,679,000	53,569,000
Corporate bonds [Member] \| Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Cash and cash equivalents		4,562,000
Marketable securities	133,438,000	141,124,000
Corporate bonds [Member] \| Fair Value Inputs Level2 [Member]
Fair value measurements
Cash and cash equivalents		4,562,000
Marketable securities	133,438,000	141,124,000
U. S. government agency securities [Member] \| Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Marketable securities	14,158,000	18,688,000
U. S. government agency securities [Member] \| Fair Value Inputs Level2 [Member]
Fair value measurements
Marketable securities	14,158,000	18,688,000
Asset backed securities [Member] \| Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Marketable securities	52,879,000	60,820,000
Asset backed securities [Member] \| Fair Value Inputs Level2 [Member]
Fair value measurements
Marketable securities	52,879,000	60,820,000
Commercial Paper [Member]. \| Estimate Of Fair Value Fair Value Disclosure [Member]
Fair value measurements
Marketable securities	3,997,000	3,993,000
Commercial Paper [Member]. \| Fair Value Inputs Level2 [Member]
Fair value measurements
Marketable securities	$ 3,997,000	$ 3,993,000