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

9 Months Ended

Sep. 30, 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 September 30, 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	$	154,137	$	—	$	—	$	154,137
U.S. Treasury securities		28,223		13		(1)		28,235
Corporate debt securities		101,018		236		(40)		101,214
Total		283,378		249		(41)		283,586
Less amounts classified as cash and cash equivalents		(154,137)		—		—		(154,137)
Total available-for-sale securities	$	129,241	$	249	$	(41)	$	129,449

	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

The following table represents the fair value hierarchy for our cash equivalents and available-for-sale securities by major security type as of September 30, 2016 and December 31, 2015 (in thousands):

	As of September 30, 2016
	Level 1		Level 2		Level 3		Total
Cash and money market funds	$	154,137	$	—	$	—	$	154,137
U.S. Treasury securities		28,235		—		—		28,235
Corporate debt securities		—		101,214		—		101,214
Total	$	182,372	$	101,214	$	—	$	283,586

	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