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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$ 44,089	$ 101,501
Less Than 12 Months - Gross Unrealized Losses	(46)	(256)
More Than 12 Months - Estimated Fair Value	3,398	6,301
More Than 12 Months - Gross Unrealized Losses	(1)	(7)
Total - Estimated Fair Value	47,487	107,802
Total - Gross Unrealized Losses	(47)	(263)
Government-sponsored enterprise securities (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	5,002	9,950
Less Than 12 Months - Gross Unrealized Losses	(2)	(57)
Total - Estimated Fair Value	5,002	9,950
Total - Gross Unrealized Losses	(2)	(57)
Commercial paper (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	4,967	7,834
Less Than 12 Months - Gross Unrealized Losses	(1)	(2)
Total - Estimated Fair Value	4,967	7,834
Total - Gross Unrealized Losses	(1)	(2)
Corporate notes (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	25,533	61,006
Less Than 12 Months - Gross Unrealized Losses	(16)	(71)
More Than 12 Months - Estimated Fair Value	3,398	6,301
More Than 12 Months - Gross Unrealized Losses	(1)	(7)
Total - Estimated Fair Value	28,931	67,307
Total - Gross Unrealized Losses	(17)	(78)
Corporate notes (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	8,587	22,711
Less Than 12 Months - Gross Unrealized Losses	(27)	(126)
Total - Estimated Fair Value	8,587	22,711
Total - Gross Unrealized Losses	$ (27)	$ (126)

X

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
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+ References

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