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

3 Months Ended

Mar. 31, 2017

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, 2017
			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	$	67,753	$	—	$	—	$	67,753
U.S. Treasury securities		24,701		7		(98)		24,610
Corporate debt securities		168,267		68		(468)		167,867
Total		260,721		75		(566)		260,230
Less amounts classified as cash and cash equivalents		(67,753)		—		—		(67,753)
Total available-for-sale securities	$	192,968	$	75	$	(566)	$	192,477

	As of December 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	$	84,783	$	—	$	—	$	84,783
U.S. Treasury securities		24,780		7		(110)		24,677
Corporate debt securities		160,571		52		(564)		160,059
Total		270,134		59		(674)		269,519
Less amounts classified as cash and cash equivalents		(84,783)		—		—		(84,783)
Total available-for-sale securities	$	185,351	$	59	$	(674)	$	184,736

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 March 31, 2017 and December 31, 2016 (in thousands):

	As of March 31, 2017
	Level 1		Level 2		Level 3		Total
Cash and money market funds	$	67,753	$	—	$	—	$	67,753
U.S. Treasury securities		24,610		—		—		24,610
Corporate debt securities		—		167,867		—		167,867
Total	$	92,363	$	167,867	$	—	$	260,230

	As of December 31, 2016
	Level 1		Level 2		Level 3		Total
Cash and money market funds	$	84,783	$	—	$	—	$	84,783
U.S. Treasury securities		24,677		—		—		24,677
Corporate debt securities		—		160,059		—		160,059
Total	$	109,460	$	160,059	$	—	$	269,519