INVESTMENTS (DETAILS) (USD $)	3 Months Ended	6 Months Ended
	Mar. 31, 2010	Jun. 30, 2011	Jun. 30, 2010
Available For Sale Securities Balance Sheet Reported Amounts Abstract
Available For Sale Securities Current		$ 655,600,000
Available For Sale Securities Noncurrent		22,400,000
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis		683,480,000
Available For Sale Securities Gross Unrealized Gains		1,281,000
Available For Sale Securities Gross Unrealized Losses		(6,827,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities		0
Available For Sale Securities Fair Value Disclosure		677,934,000
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		99,986,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value		19,884,000
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		136,000
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses		6,691,000
Available For Sale Securities Gross Realized Gain Loss Abstract
Other Comprehensive Income Available For Sale Securities Adjustment Before Tax Period Increase Decrease		200,000
Available For Sale Securities Debt Maturities Amortized Cost Abstract
Available For Sale Securities Debt Maturities Within One Year Amortized Cost		327,303,000
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost		329,602,000
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost		26,575,000
Available For Sale Securities Debt Maturities Fair Value Abstract
Available For Sale Securities Debt Maturities Within One Year Fair Value		327,965,000
Available For Sale Securities Debt Maturities After One Through Five Years Fair Value		330,085,000
Available For Sale Securities Debt Maturities After Ten Years Fair Value		19,884,000
Available For Sale Securities Other Disclosure Items Abstract
Other Than Temporary Impairment Loss Recognized	300,000	0	260,000
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis		360,758,000
Available For Sale Securities Gross Unrealized Gains		474,000
Available For Sale Securities Gross Unrealized Losses		(128,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities		0
Available For Sale Securities Fair Value Disclosure		361,104,000
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		79,304,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value		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		128,000
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses		0
US Treasury And Government [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis		251,136,000
Available For Sale Securities Gross Unrealized Gains		769,000
Available For Sale Securities Gross Unrealized Losses		(8,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities		0
Available For Sale Securities Fair Value Disclosure		251,897,000
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		18,892,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value		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
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses		0
Auction Rate Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis		26,575,000
Available For Sale Securities Gross Unrealized Gains		0
Available For Sale Securities Gross Unrealized Losses		(6,691,000)
Other Than Temporary Impairment Losses Investments Available For Sale Securities		0
Available For Sale Securities Fair Value Disclosure		19,884,000
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
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value		19,884,000
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
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses		6,691,000
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available For Sale Debt Securities Amortized Cost Basis		45,011,000
Available For Sale Securities Gross Unrealized Gains		38,000
Available For Sale Securities Gross Unrealized Losses		0
Other Than Temporary Impairment Losses Investments Available For Sale Securities		0
Available For Sale Securities Fair Value Disclosure		45,049,000
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		1,790,000
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value		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		0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses		$ 0