FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Included in cash and cash equivalents:
Amortized Cost	$ 11,193	$ 19,177
Gross Unrealized Losses		(1)
Estimated Fair Value	11,193	19,176
Restricted cash:
Amortized Cost	268	267
Estimated Fair Value	268	267
Marketable securities:
Amortized Cost	116,042	125,397
Gross Unrealized Gains	54	50
Gross Unrealized Losses	(107)	(262)
Estimated Fair Value	115,989	125,185
Money market funds
Included in cash and cash equivalents:
Amortized Cost	11,193	4,577
Estimated Fair Value	11,193	4,577
Commercial paper
Included in cash and cash equivalents:
Amortized Cost		7,599
Estimated Fair Value		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		5,002
Gross Unrealized Losses		(1)
Estimated Fair Value		5,001
Certificate of deposit
Restricted cash:
Amortized Cost	268	267
Estimated Fair Value	268	267
Government-sponsored enterprise securities (due in less than one year)
Marketable securities:
Amortized Cost	5,000
Gross Unrealized Losses	(3)
Estimated Fair Value	4,997
Government-sponsored enterprise securities (due in one to two years)
Marketable securities:
Amortized Cost	12,500	10,007
Gross Unrealized Losses	(42)	(57)
Estimated Fair Value	12,458	9,950
Commercial paper (due in less than one year)
Marketable securities:
Amortized Cost	31,024	27,661
Gross Unrealized Gains	50	49
Gross Unrealized Losses	(5)	(2)
Estimated Fair Value	31,069	27,708
Corporate notes (due in less than one year)
Marketable securities:
Amortized Cost	66,012	64,892
Gross Unrealized Gains	4	1
Gross Unrealized Losses	(47)	(77)
Estimated Fair Value	65,969	64,816
Corporate notes (due in one to two years)
Marketable securities:
Amortized Cost	1,506	22,837
Gross Unrealized Losses	(10)	(126)
Estimated Fair Value	$ 1,496	$ 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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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Fair value portion 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.

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Amount of 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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The aggregate value of all restricted investments.

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