FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Fair value amounts included in the carrying value of
Cash and cash equivalents	$ 362,787	$ 370,323	$ 312,020	$ 211,349
Short-term investments	647,284	781,134
Investments	41,240	42,940
Asset transfers between Level 1 and Level 2 measurements	0	0
Level 1
Fair value amounts included in the carrying value of
Cash and cash equivalents	359,992	303,018
Total	359,992	303,018
Level 2
Fair value amounts included in the carrying value of
Cash and cash equivalents	2,795	67,305
Short-term investments	643,374	777,224
Accounts receivable, net	393	83
Investments	41,240	42,940
Accrued liabilities	(177)	(335)
Total	687,625	887,217
Level 3
Fair value amounts included in the carrying value of
Short-term investments	3,910	3,910
Prepaid expenses and other current assets	250	250
Total	4,160	4,160
Total fair value
Fair value amounts included in the carrying value of
Cash and cash equivalents	362,787	370,323
Short-term investments	647,284	781,134
Accounts receivable, net	393	83
Investments	41,240	42,940
Prepaid expenses and other current assets	250	250
Accrued liabilities	(177)	(335)
Total	$ 1,051,777	$ 1,194,395