MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2013

Marketable Securities and Fair Value Measurements [Abstract]

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

March 31, 2013	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Security type
Corporate debt securities-short term	$	72,087	$	53	$	(6	)	$	72,134
Corporate debt securities-long term		30,682		69		(5	)		30,746
Total available-for-sale marketable securities	$	102,769	$	122	$	(11	)	$	102,880

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

Schedule of fair value of trading securities

March 31, 2013	Amortized Cost			Gross Unrealized Gains			Gross Unrealized Losses				Fair Value
Security type
Auction rate securities		$	2,100		$	—		$	(313	)		$	1,787
Total trading securities		$	2,100		$	—		$	(313	)		$	1,787

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

Schedule of assets measured at fair value on a recurring basis

	March 31, 2013		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents	$	12,728	$	12,728	$	—	$	—
Corporate debt securities-short term		72,134		—		72,134		—
Corporate debt securities-long term		30,746		—		30,746		—
Auction rate securities-long term		1,787		—		—		1,787
Total	$	117,395	$	12,728	$	102,880	$	1,787

	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

Schedule of fair value of auction rate securities

	Amount
Balance at December 31, 2012	$	1,789
Loss on auction rate securities		(2	)
Balance at March 31, 2013	$	1,787

	Amount
Balance at December 31, 2011	$	1,676
Gain on auction rate securities		85
Balance at March 31, 2012	$	1,761

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

	Estimated Fair Value at March 31, 2013		Valuation Technique	Unobservable Inputs	Range
Auction rate securities	$	1,787	Discounted cash flow
				Maximum rate	1.56	%
				Liquidity risk premium	3.50%–4.50	%
				Probability of earning maximum rate until maturity	0.06%–0.10	%
				Probability of principal returned prior to maturity	86.20%–88.26	%
				Probability of default	11.69%–13.71	%