MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2012

Marketable Securities and Fair Value Measurements [Abstract]

Schedule of fair value of available-for-sale marketable securities

December 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Security type
Corporate debt securities-short term	$	64,921	$	45	$	(22	)	$	64,944
Corporate debt securities-long term		49,460		93		(14	)		49,539
Total available-for-sale marketable securities	$	114,381	$	138	$	(36	)	$	114,483

December 31, 2011	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Security type
U.S. Federal Treasury and U.S. government agencies securities-short term	$	17,259	$	1	$	(1	)	$	17,259
Corporate debt securities-short term		39,828		22		(36	)		39,814
		57,087		23		(37	)		57,073
U.S. Federal Treasury and U.S. government agencies securities-long term		33,556		13		(6	)		33,563
Corporate debt securities-long term		5,235		2		(1	)		5,236
		38,791		15		(7	)		38,799
Total available-for-sale marketable securities	$	95,878	$	38	$	(44	)	$	95,872

Schedule of fair value of trading securities

December 31, 2012	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Security type
Auction rate securities	$	2,100	$	—	$	(311	)	$	1,789
Total trading securities	$	2,100	$	—	$	(311	)	$	1,789

December 31, 2011	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Security type
Auction rate securities	$	2,100	$	—	$	(424	)	$	1,676
Total trading securities	$	2,100	$	—	$	(424	)	$	1,676

Schedule of assets measured at fair value on a recurring basis

	December 31, 2012		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	11,754	$	11,754	$	—	$	—
Corporate debt securities-short term		64,944		—		64,944		—
Corporate debt securities-long term		49,539		—		49,539		—
Auction rate securities-long term		1,789		—		—		1,789
Total	$	128,026	$	11,754	$	114,483	$	1,789

	December 31, 2011		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	10,042	$	10,042	$	—	$	—
U.S. Federal Treasury and U.S. government agencies securities-short term		17,259		—		17,259		—
Corporate debt securities-short term		39,814		—		39,814		—
U.S. Federal Treasury and U.S. government agencies securities-long term		33,563		—		33,563		—
Corporate debt securities-long term		5,236		—		5,236		—
Auction rate securities-long term		1,676		—		—		1,676
Total	$	107,590	$	10,042	$	95,872	$	1,676

Schedule of fair value of auction rate securities

	Amount
Balance at Deceber 31, 2011	$	1,676
Gain on auction rate securities		113
Settlements		—
Balance at December 31, 2012	$	1,789

	Amount
Balance at December 31, 2010	$	2,154
Gain on auction rate securities		20
Settlements		(498	)
Balance at December 31, 2011	$	1,676

Schedule of quantitative information on the unobservable inputs of our fair value measurements for our Level 3 assets

	Estimated Fair Value at December 31, 2012		Valuation Technique	Unobservable Inputs	Range
Auction rate securities	$	1,789	Discounted cash flow
				Maximum rate		1.62	%
				Liquidity risk premium		3.50%–4.50	%
				Probability of earning maximum rate until maturity		0.06%–0.09	%
				Probability of principal returned prior to maturity		86.34%–88.38	%
				Probability of default		11.57%–13.57	%