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FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Included in cash and cash equivalents
Amortized Cost	$ 10,546	$ 19,177
Gross Unrealized Gains	1
Gross Unrealized Losses		(1)
Estimated Fair Value	10,547	19,176
Restricted cash
Amortized Cost	267	267
Estimated Fair Value	267	267
Marketable securities
Amortized Cost	128,783	125,397
Gross Unrealized Gains	86	50
Gross Unrealized Losses	(47)	(262)
Estimated Fair Value	128,822	125,185
Money market funds
Included in cash and cash equivalents
Amortized Cost	3,798	4,577
Estimated Fair Value	3,798	4,577
Commercial paper
Included in cash and cash equivalents
Amortized Cost	3,497	7,599
Gross Unrealized Gains	1
Estimated Fair Value	3,498	7,599
Government-sponsored enterprise securities
Included in cash and cash equivalents
Amortized Cost		1,999
Estimated Fair Value		1,999
Corporate notes
Included in cash and cash equivalents
Amortized Cost	3,251	5,002
Gross Unrealized Losses		(1)
Estimated Fair Value	3,251	5,001
Certificate of deposit
Restricted cash
Amortized Cost	267	267
Estimated Fair Value	267	267
Government-sponsored enterprise securities (due in 1 to 2 years)
Marketable securities
Amortized Cost	17,021	10,007
Gross Unrealized Gains	1
Gross Unrealized Losses	(2)	(57)
Estimated Fair Value	17,020	9,950
Commercial paper (due in less than 1 year)
Marketable securities
Amortized Cost	34,605	27,661
Gross Unrealized Gains	58	49
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	34,662	27,708
Corporate notes (due in less than 1 year)
Marketable securities
Amortized Cost	62,186	64,892
Gross Unrealized Gains	15	1
Gross Unrealized Losses	(17)	(77)
Estimated Fair Value	62,184	64,816
Corporate notes (due in 1 to 2 years)
Marketable securities
Amortized Cost	14,971	22,837
Gross Unrealized Gains	12
Gross Unrealized Losses	(27)	(126)
Estimated Fair Value	$ 14,956	$ 22,711

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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 before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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