FAIR VALUE MEASUREMENTS (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 1,515,971,000	$ 1,579,003,000	$ 1,645,616,000	$ 1,853,988,000
State and municipal bonds	1,141,310,000	1,032,954,000
US Treasury securities	80,879,000	91,340,000
Government-sponsored enterprise securities	24,532,000	143,278,000
Residential mortgage-backed securities	350,881,000	368,798,000
Commercial mortgage-backed securities	13,935,000	14,825,000
Asset-backed securities	9,939,000	13,504,000
Corporate debt and other securities	1,071,853,000	1,065,500,000
Total	4,209,300,000	4,309,202,000
Debt Instruments [Abstract]
Senior Notes, Carrying Value	1,580,000,000	1,820,000,000
Senior Notes, Fair Value	1,770,000,000	1,990,000,000
Quoted Prices in Active Markets for Identical Assets, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	1,365,943,000	1,449,883,000
State and municipal bonds	0	0
US Treasury securities	80,879,000	91,340,000
Government-sponsored enterprise securities	0	0
Residential mortgage-backed securities	0	0
Commercial mortgage-backed securities	0	0
Asset-backed securities	0	0
Corporate debt and other securities	0	11,598,000
Total	1,446,822,000	1,552,821,000
Significant Other Observable Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	150,028,000	129,120,000
State and municipal bonds	1,141,310,000	1,032,954,000
US Treasury securities	0	0
Government-sponsored enterprise securities	24,532,000	143,278,000
Residential mortgage-backed securities	350,881,000	368,798,000
Commercial mortgage-backed securities	13,935,000	14,825,000
Asset-backed securities	9,939,000	13,504,000
Corporate debt and other securities	1,071,853,000	1,053,902,000
Total	2,762,478,000	2,756,381,000
Significant Unobservable Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
State and municipal bonds	0	0
US Treasury securities	0	0
Government-sponsored enterprise securities	0	0
Residential mortgage-backed securities	0	0
Commercial mortgage-backed securities	0	0
Asset-backed securities	0	0
Corporate debt and other securities	0	0
Total	$ 0	$ 0