INVESTMENTS (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 D	Dec. 31, 2011
INVESTMENTS
Number of days for settlement basis, VRDNs to be liquidated at par	7
Disclosure of underlying contractual maturities of investments
Amortized Cost	$ 115,952	$ 434,476
Fair Value	118,424	434,420
U.S. Treasuries | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost	16,040	8,034
Fair Value	16,040	8,039
Certificates of deposit | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost	2,201	29,034
Fair Value	2,201	29,035
Corporate bonds | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost		2,022
Fair Value		2,022
Municipal securities | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost	77,038	284,605
Fair Value	77,027	284,541
U.S. government agency securities | Less than 1 year
Disclosure of underlying contractual maturities of investments
Amortized Cost		16,005
Fair Value		16,007
Variable rate demand notes | Due 1 - 10 years
Disclosure of underlying contractual maturities of investments
Amortized Cost		5,775
Fair Value		5,775
Variable rate demand notes | Due 11 - 20 years
Disclosure of underlying contractual maturities of investments
Amortized Cost		12,716
Fair Value		12,716
Variable rate demand notes | Due 21 - 30 years
Disclosure of underlying contractual maturities of investments
Amortized Cost		27,902
Fair Value		27,902
Variable rate demand notes | Due 31 - 40 years
Disclosure of underlying contractual maturities of investments
Amortized Cost		12,532
Fair Value		12,532
Auction rate securities | Due 11 - 20 years
Disclosure of underlying contractual maturities of investments
Amortized Cost	10,748	5,158
Fair Value	10,748	5,158
Auction rate securities | Due 21 - 30 years
Disclosure of underlying contractual maturities of investments
Amortized Cost	9,925	25,134
Fair Value	12,408	25,134
Auction rate securities | Due 31 - 40 years
Disclosure of underlying contractual maturities of investments
Amortized Cost		5,559
Fair Value		$ 5,559