CASH, CASH EQUIVALENTS AND INVESTMENTS - Schedule of Cash, Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Investments, Amortized Cost Basis	$ 247,230	$ 300,333
Investments, Gross Unrealized Gains	7	4
Investments, Gross Unrealized Losses	(568)	(169)
Investments	246,669	300,168
Certificates of Deposit [Member]
Cash and Cash Equivalents [Line Items]
Cash Equivalents, at Carrying Value	6,855	11,532
Cash Equivalents, Gross Unrealized Gain	7	3
Cash Equivalents, Gross Unrealized Losses	(2)	(14)
Cash and Cash Equivalents, Fair Value Disclosure	6,860	11,521
Corporate Debt Securities [Member]
Cash and Cash Equivalents [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	224,376	233,848
Available-for-sale Securities, Gross Unrealized Losses	(247)	(139)
Available-for-sale Securities, Fair Value Disclosure	224,129	233,709
US Treasury and Government [Member]
Cash and Cash Equivalents [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	15,999	54,953
Available-for-sale Securities, Gross Unrealized Gains		1
Available-for-sale Securities, Gross Unrealized Losses	(319)	(16)
Available-for-sale Securities, Fair Value Disclosure	$ 15,680	$ 54,938