INVESTMENTS (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Disclosure of underlying contractual maturities of investments
Amortized Cost	$ 505,651	$ 412,039
Fair Value	505,751	412,087
Certificates of deposit | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost	6,007	22,045
Fair Value	6,007	22,045
Commercial paper | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost	9,996	5,991
Fair Value	9,996	5,991
Municipal securities | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost	431,597	367,819
Fair Value	431,673	367,867
Municipal securities | Due 1 - 10 years
Disclosure of underlying contractual maturities of investments
Amortized Cost	45,232
Fair Value	45,256
Auction rate securities
Disclosure of underlying contractual maturities of investments
Amortized Cost	12,800
Auction rate securities | Due 11 - 20 years
Disclosure of underlying contractual maturities of investments
Amortized Cost	12,773	11,102
Fair Value	12,773	11,102
Auction rate securities | Due 21 - 30 years
Disclosure of underlying contractual maturities of investments
Amortized Cost	46	5,082
Fair Value	$ 46	$ 5,082