FAIR VALUE MEASUREMENTS FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 1,399,162	$ 1,579,003	$ 1,853,988	$ 1,418,554
State and municipal bonds	1,253,789	1,032,954
U.S. Treasury securities	78,931	91,340
Government-sponsored enterprise securities	73,532	143,278
Residential mortgage-backed securities	312,641	368,798
Commercial mortgage-backed securities	21,590	14,825
Asset-backed securities	23,626	13,504
Corporate debt and other securities	991,610	1,065,500
Total	4,154,881	4,309,202
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	1,218,046	1,449,883
State and municipal bonds	0	0
U.S. Treasury securities	78,931	91,340
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
Total	1,296,977	1,552,821
Significant Other Observable Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	181,116	129,120
State and municipal bonds	1,253,789	1,032,954
U.S. Treasury securities	0	0
Government-sponsored enterprise securities	73,532	143,278
Residential mortgage-backed securities	312,641	368,798
Commercial mortgage-backed securities	21,590	14,825
Asset-backed securities	23,626	13,504
Corporate debt and other securities	991,610	1,053,902
Total	2,857,904	2,756,381
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
U.S. 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