FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Included in cash and cash equivalents
Amortized Cost	$ 5,784	$ 19,177
Gross Unrealized Losses		(1)
Estimated Fair Value	5,784	19,176
Restricted cash
Amortized Cost	267	267
Estimated Fair Value	267	267
Marketable securities
Amortized Cost	127,835	125,397
Gross Unrealized Gains	115	50
Gross Unrealized Losses	(25)	(262)
Estimated Fair Value	127,925	125,185
Money market funds
Included in cash and cash equivalents
Amortized Cost	4,284	4,577
Estimated Fair Value	4,284	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	1,500	5,002
Gross Unrealized Losses		(1)
Estimated Fair Value	1,500	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	17,006	10,007
Gross Unrealized Gains	5
Gross Unrealized Losses		(57)
Estimated Fair Value	17,011	9,950
Commercial paper (due in less than 1 year)
Marketable securities
Amortized Cost	40,000	27,661
Gross Unrealized Gains	63	49
Gross Unrealized Losses	(4)	(2)
Estimated Fair Value	40,059	27,708
Corporate notes (due in less than 1 year)
Marketable securities
Amortized Cost	62,330	64,892
Gross Unrealized Gains	29	1
Gross Unrealized Losses	(16)	(77)
Estimated Fair Value	62,343	64,816
Corporate notes (due in 1 to 2 years)
Marketable securities
Amortized Cost	8,499	22,837
Gross Unrealized Gains	18
Gross Unrealized Losses	(5)	(126)
Estimated Fair Value	$ 8,512	$ 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 carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

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The aggregate value of all restricted investments.

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