INVESTMENTS (DETAILS) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Available For Sale Securities Balance Sheet Reported Amounts Abstract
Available For Sale Securities Noncurrent	$ 12,800,000			$ 12,800,000
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	644,121,000	290,573,000		644,121,000
Available For Sale Securities Gross Unrealized Gains	3,061,000	382,000		3,061,000
Available For Sale Securities Gross Unrealized Losses	(4,596,000)	(5,188,000)		(4,596,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	642,586,000	285,767,000		642,586,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value Abstract
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	65,396,000			65,396,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	12,778,000			12,778,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Abstract
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses	(24,000)			(24,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(4,572,000)			(4,572,000)
Available For Sale Securities Gross Realized Gain Loss Abstract
Available For Sale Securities Gross Realized Gains	100,000		100,000	100,000	100,000
Available For Sale Securities Debt Maturities Amortized Cost Abstract
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	309,421,000			309,421,000
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	317,350,000			317,350,000
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost	17,350,000			17,350,000
Available For Sale Securities Debt Maturities Fair Value Abstract
Available For Sale Securities Debt Maturities Within One Year Fair Value	311,520,000			311,520,000
Available For Sale Securities Debt Maturities After One Through Five Years Fair Value	318,288,000			318,288,000
Available For Sale Securities Debt Maturities After Ten Years Fair Value	12,778,000			12,778,000
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	323,691,000	138,554,000		323,691,000
Available For Sale Securities Gross Unrealized Gains	2,674,000	161,000		2,674,000
Available For Sale Securities Gross Unrealized Losses	(8,000)	(549,000)		(8,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	326,357,000	138,166,000		326,357,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value Abstract
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	24,412,000			24,412,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	0			0
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Abstract
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses	(8,000)			(8,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0			0
US Treasury And Government [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	254,072,000	125,092,000		254,072,000
Available For Sale Securities Gross Unrealized Gains	324,000	221,000		324,000
Available For Sale Securities Gross Unrealized Losses	(15,000)	(24,000)		(15,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	254,381,000	125,289,000		254,381,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value Abstract
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	28,965,000			28,965,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	0			0
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Abstract
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses	(15,000)			(15,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0			0
Auction Rate Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	17,350,000	17,400,000		17,350,000
Available For Sale Securities Gross Unrealized Gains	0	0		0
Available For Sale Securities Gross Unrealized Losses	(4,572,000)	(4,607,000)		(4,572,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	12,778,000	12,793,000		12,778,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value Abstract
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	0			0
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	12,778,000			12,778,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Abstract
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses	0			0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(4,572,000)			(4,572,000)
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	49,008,000	9,527,000		49,008,000
Available For Sale Securities Gross Unrealized Gains	63,000	0		63,000
Available For Sale Securities Gross Unrealized Losses	(1,000)	(8,000)		(1,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	49,070,000	9,519,000		49,070,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value Abstract
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	12,019,000			12,019,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	0			0
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Abstract
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses	(1,000)			(1,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 0			$ 0