CASH, CASH EQUIVALENTS, AND AVAILABLE-FOR-SALE SECURITIES (Tables)

3 Months Ended

Mar. 31, 2016

CASH, CASH EQUIVALENTS, AND AVAILABLE-FOR-SALE SECURITIES

Schedule of fair value and amortized cost of cash, cash equivalents, and available-for-sale securities by major security type

	As of March 31, 2016
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
Cash and cash equivalents and available-for-sale securities	Cost		Gains		Losses		Fair Value
Cash and money market funds	$	83,701	$	—	$	—	$	83,701
U.S. Treasury securities		60,819		13		(4)		60,828
Corporate debt securities		83,115		187		(21)		83,281
Total		227,635		200		(25)		227,810
Less amounts classified as cash and cash equivalents		(83,701)		—		—		(83,701)
Total available-for-sale securities	$	143,934	$	200	$	(25)	$	144,109

	As of December 31, 2015
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
Cash and cash equivalents and available-for-sale securities	Cost		Gains		Losses		Fair Value
Cash and money market funds	$	95,395	$	—	$	—	$	95,395
U.S. Treasury securities		84,734		—		(107)		84,627
Corporate debt securities		61,696		20		(175)		61,541
Total		241,825		20		(282)		241,563
Less amounts classified as cash and cash equivalents		(95,395)		—		—		(95,395)
Total available-for-sale securities	$	146,430	$	20	$	(282)	$	146,168

Schedule of Fair Value of Separate Accounts by Major Category of Investment [Table Text Block]

The following table represents the fair value hierarchy for our cash equivalents and available-for-sale securities by major security type as of March 31, 2016 and December 31, 2015 (in thousands):

	As of March 31, 2016
	Level 1		Level 2		Level 3		Total
Cash and money market funds	$	83,701	$	—	$	—	$	83,701
U.S. Treasury securities		60,828		—		—		60,828
Corporate debt securities		—		83,281		—		83,281
Total	$	144,529	$	83,281	$	—	$	227,810

	As of December 31, 2015
	Level 1		Level 2		Level 3		Total
Cash and money market funds	$	95,395	$	—	$	—	$	95,395
U.S. Treasury securities		84,627		—		—		84,627
Corporate debt securities		—		61,541		—		61,541
Total	$	180,022	$	61,541	$	—	$	241,563