INVESTMENTS (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Held-to-maturity securities:
Estimated Fair Value	$ 1,619
Total investments
Amortized Cost	592,851	$ 577,864
Gross Unrealized Gains	540	127
Gross Unrealized Losses, Less than One Year	(232)	(368)
Gross Unrealized Losses, Greater than One Year		(41)
Estimated Fair Value	593,159	577,582
Short-term investments
Available-for-sale securities:
Amortized Cost	548,955	407,061
Gross Unrealized Gains	540	127
Gross Unrealized Losses, Less than One Year	(75)	(86)
Estimated Fair Value	549,420	407,102
Short-term investments | U.S. government and agency debt securities
Available-for-sale securities:
Amortized Cost	306,522	226,387
Gross Unrealized Gains	433	88
Gross Unrealized Losses, Less than One Year	(6)	(15)
Estimated Fair Value	306,949	226,460
Short-term investments | Corporate debt securities
Available-for-sale securities:
Amortized Cost	211,428	140,900
Gross Unrealized Gains	95	26
Gross Unrealized Losses, Less than One Year	(62)	(66)
Estimated Fair Value	211,461	140,860
Short-term investments | International government agency debt securities
Available-for-sale securities:
Amortized Cost	31,005	39,774
Gross Unrealized Gains	12	13
Gross Unrealized Losses, Less than One Year	(7)	(5)
Estimated Fair Value	31,010	39,782
Long-term investments
Available-for-sale securities:
Amortized Cost	42,277	169,184
Gross Unrealized Losses, Less than One Year	(157)	(282)
Gross Unrealized Losses, Greater than One Year		(41)
Estimated Fair Value	42,120	168,861
Total investments
Total long-term investments	43,896	170,803
Long Term Investments	43,739	170,480
Total long-term investments	43,739	170,480
Long-term investments | Certificates of deposit
Held-to-maturity securities:
Amortized Cost	1,619	1,619
Estimated Fair Value	1,619	1,619
Long-term investments | U.S. government and agency debt securities
Available-for-sale securities:
Amortized Cost	12,998	100,429
Gross Unrealized Losses, Less than One Year	(6)	(196)
Gross Unrealized Losses, Greater than One Year		(40)
Estimated Fair Value	12,992	100,193
Long-term investments | Corporate debt securities
Available-for-sale securities:
Amortized Cost	29,279	61,187
Gross Unrealized Losses, Less than One Year	(151)	(84)
Estimated Fair Value	$ 29,128	61,103
Long-term investments | International government agency debt securities
Available-for-sale securities:
Amortized Cost		7,568
Gross Unrealized Losses, Less than One Year		(2)
Gross Unrealized Losses, Greater than One Year		(1)
Estimated Fair Value		$ 7,565