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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$ 101,501	$ 111,321
Less Than 12 Months - Gross Unrealized Losses	(256)	(100)
More Than 12 Months - Estimated Fair Value	6,301
More Than 12 Months - Gross Unrealized Losses	(7)
Total - Estimated Fair Value	107,802	111,321
Total - Gross Unrealized Losses	(263)	(100)
Government-sponsored enterprise securities (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value		400
Less Than 12 Months - Gross Unrealized Losses		(1)
Total - Estimated Fair Value		400
Total - Gross Unrealized Losses		(1)
Government-sponsored enterprise securities (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	9,950	5,549
Less Than 12 Months - Gross Unrealized Losses	(57)	(7)
Total - Estimated Fair Value	9,950	5,549
Total - Gross Unrealized Losses	(57)	(7)
Commercial paper (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	7,834
Less Than 12 Months - Gross Unrealized Losses	(2)
Total - Estimated Fair Value	7,834
Total - Gross Unrealized Losses	(2)
Corporate notes (due in less than 1 year)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	61,006	92,989
Less Than 12 Months - Gross Unrealized Losses	(71)	(63)
More Than 12 Months - Estimated Fair Value	6,301
More Than 12 Months - Gross Unrealized Losses	(7)
Total - Estimated Fair Value	67,307	92,989
Total - Gross Unrealized Losses	(78)	(63)
Corporate notes (due in 1 to 2 years)
Marketable securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	22,711	12,383
Less Than 12 Months - Gross Unrealized Losses	(126)	(29)
Total - Estimated Fair Value	22,711	12,383
Total - Gross Unrealized Losses	$ (126)	$ (29)

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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