INVESTMENTS (DETAILS) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012
Available For Sale Securities Balance Sheet Reported Amounts Abstract
Available For Sale Securities Current	$ 573,500,000		$ 573,500,000
Available For Sale Securities Noncurrent	22,600,000		22,600,000
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	600,374,000	290,573,000	600,374,000
Available For Sale Securities Gross Unrealized Gains	579,000	382,000	579,000
Available For Sale Securities Gross Unrealized Losses	(4,869,000)	(5,188,000)	(4,869,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	596,084,000	285,767,000	596,084,000
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	297,238,000		297,238,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	14,724,000		14,724,000
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	(243,000)		(243,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(4,626,000)		(4,626,000)
Available For Sale Securities Gross Realized Gain Loss Abstract
Available For Sale Securities Gross Realized Gains			100,000
Other Comprehensive Income Available For Sale Securities Adjustment Before Tax Period Increase Decrease			300,000
Available For Sale Securities Debt Maturities Amortized Cost Abstract
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	261,275,000		261,275,000
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	321,749,000		321,749,000
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	261,399,000		261,399,000
Available For Sale Securities Debt Maturities After One Through Five Years Fair Value	321,919,000		321,919,000
Available For Sale Securities Debt Maturities After Ten Years Fair Value	12,766,000		12,766,000
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	299,940,000	138,554,000	299,940,000
Available For Sale Securities Gross Unrealized Gains	338,000	161,000	338,000
Available For Sale Securities Gross Unrealized Losses	(212,000)	(549,000)	(212,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	300,066,000	138,166,000	300,066,000
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	144,330,000		144,330,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value	1,958,000		1,958,000
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	(170,000)		(170,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(42,000)		(42,000)
US Treasury And Government [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	236,684,000	125,092,000	236,684,000
Available For Sale Securities Gross Unrealized Gains	220,000	221,000	220,000
Available For Sale Securities Gross Unrealized Losses	(59,000)	(24,000)	(59,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	236,845,000	125,289,000	236,845,000
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	136,641,000		136,641,000
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	(59,000)		(59,000)
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	(4,584,000)	(4,607,000)	(4,584,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	12,766,000	12,793,000	12,766,000
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	12,766,000		12,766,000
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	(4,584,000)		(4,584,000)
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis	46,400,000	9,527,000	46,400,000
Available For Sale Securities Gross Unrealized Gains	21,000	0	21,000
Available For Sale Securities Gross Unrealized Losses	(14,000)	(8,000)	(14,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities	0	0
Available For Sale Securities Fair Value Disclosure	46,407,000	9,519,000	46,407,000
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	16,267,000		16,267,000
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	(14,000)		(14,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	$ 0		$ 0