FAIR VALUE MEASUREMENTS (Details) (Recurring basis, USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Level 1
Fair value
Assets, Total	$ 127,795	$ 92,873
Level 2
Fair value
Assets, Total	396,230	186,541
Liabilities, Total	(92)	(275)
Level 3
Fair value
Assets, Total		1,526
Total
Fair value
Assets, Total	524,025	280,940
Liabilities, Total	(92)	(275)
Interest rate swap contract | Level 2
Fair value
Interest rate swap contract	(92)	(275)
Interest rate swap contract | Total
Fair value
Interest rate swap contract	(92)	(275)
Cash equivalents | Level 1
Fair value
Available for sale securities	1,201	1,201
Cash equivalents | Total
Fair value
Available for sale securities	1,201	1,201
U.S. government and agency debt securities | Level 1
Fair value
Available for sale securities	126,594	63,213
U.S. government and agency debt securities | Level 2
Fair value
Available for sale securities	139,028	95,974
U.S. government and agency debt securities | Total
Fair value
Available for sale securities	265,622	159,187
Corporate debt securities | Level 2
Fair value
Available for sale securities	204,597	58,809
Corporate debt securities | Total
Fair value
Available for sale securities	204,597	58,809
International government agency debt securities | Level 2
Fair value
Available for sale securities	52,605	31,758
International government agency debt securities | Total
Fair value
Available for sale securities	52,605	31,758
Equity securities | Level 1
Fair value
Available for sale securities		28,459
Equity securities | Level 3
Fair value
Available for sale securities		1,526
Equity securities | Total
Fair value
Available for sale securities		$ 29,985