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FAIR VALUE MEASUREMENTS - SECURITIES WITH UNREALIZED LOSSES (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	$ 66,534	$ 101,501
Less Than 12 Months - Gross Unrealized Losses	(97)	(256)
More Than 12 Months - Estimated Fair Value	6,944	6,301
More Than 12 Months - Gross Unrealized Losses	(10)	(7)
Total - Estimated Fair Value	73,478	107,802
Total - Gross Unrealized Losses	(107)	(263)
Government-sponsored enterprise securities (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	4,997
Less Than 12 Months - Gross Unrealized Losses	(3)
Total - Estimated Fair Value	4,997
Total - Gross Unrealized Losses	(3)
Government-sponsored enterprise securities (due in one to two years)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	12,458	9,950
Less Than 12 Months - Gross Unrealized Losses	(42)	(57)
Total - Estimated Fair Value	12,458	9,950
Total - Gross Unrealized Losses	(42)	(57)
Commercial paper (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	8,365	7,834
Less Than 12 Months - Gross Unrealized Losses	(5)	(2)
Total - Estimated Fair Value	8,365	7,834
Total - Gross Unrealized Losses	(5)	(2)
Corporate notes (due in less than one year)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	39,218	61,006
Less Than 12 Months - Gross Unrealized Losses	(37)	(71)
More Than 12 Months - Estimated Fair Value	6,944	6,301
More Than 12 Months - Gross Unrealized Losses	(10)	(7)
Total - Estimated Fair Value	46,162	67,307
Total - Gross Unrealized Losses	(47)	(78)
Corporate notes (due in one to two years)
Available for sale securities with unrealized losses
Less Than 12 Months - Estimated Fair Value	1,496	22,711
Less Than 12 Months - Gross Unrealized Losses	(10)	(126)
Total - Estimated Fair Value	1,496	22,711
Total - Gross Unrealized Losses	$ (10)	$ (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
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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+ References

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ References

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