MARKETABLE SECURITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current available-for-sale marketable securities
Amortized Cost	$ 150,942	$ 165,035
Gross Unrealized Gains	693	697
Gross Unrealized Losses	(86)	(37)
Estimated Fair Value	151,549	165,695
Contractual maturities of debt securities classified as available-for-sale
Due in one year or less, Amortized Cost	75,375
Due after one year through five years, Amortized Cost	75,567
Total, Amortized Cost	150,942
Due in one year or less, Estimated Fair Value	75,566
Due after one year through five years, Estimated Fair Value	75,983
Total, Estimated Fair Value	151,549
Total debt securities
Current available-for-sale marketable securities
Amortized Cost	150,942	160,379
Gross Unrealized Gains	693	686
Gross Unrealized Losses	(86)	(37)
Estimated Fair Value	151,549	161,028
Corporate debt securities
Current available-for-sale marketable securities
Amortized Cost	38,939	48,621
Gross Unrealized Gains	106	99
Gross Unrealized Losses	(1)	(15)
Estimated Fair Value	39,044	48,705
States of the U.S. and state political subdivisions
Current available-for-sale marketable securities
Amortized Cost	112,003	111,758
Gross Unrealized Gains	587	587
Gross Unrealized Losses	(85)	(22)
Estimated Fair Value	112,505	112,323
Marketable equity security
Current available-for-sale marketable securities
Amortized Cost		4,656
Gross Unrealized Gains		11
Estimated Fair Value		$ 4,667