FAIR VALUE MEASUREMENTS (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value of Assets Measured on a Recurring Basis

The following tables present information about our assets that are measured at fair value on a recurring basis at September 30, 2018 and December 31, 2017, and indicate the fair value hierarchy of the valuation techniques we utilized to determine such fair value, in thousands:

Description	At September 30, 2018		Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents:
Corporate notes	$	2,729	$	—	$	2,729	$	—
U.S. government-sponsored enterprise securities		1,985		—		1,985		—
U.S. treasury securities		9,974		—		9,974		—
Money market funds		232,073		232,073		—		—
Marketable debt securities:
Certificates of deposit		18,800		—		18,800		—
Commercial paper		101,376		—		101,376		—
Corporate notes		324,379		—		324,379		—
U.S. government-sponsored enterprise securities		111,339		—		111,339		—
U.S. treasury securities		349,328		—		349,328		—
Marketable equity securities		15,004		15,004		—		—
Restricted cash (money market funds)		1,476		1,476		—		—
Total	$	1,168,463	$	248,553	$	919,910	$	—

Description	At December 31, 2017		Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents:
Commercial paper	$	82,262	$	—	$	82,262	$	—
Corporate notes		18,116		—		18,116		—
U.S. government-sponsored enterprise securities		231,122		—		231,122		—
U.S. treasury securities		62,855		—		62,855		—
Money market funds		122,986		122,986		—		—
Marketable debt securities:
Certificates of deposit		30,200		—		30,200		—
Commercial paper		56,951		—		56,951		—
Corporate notes		373,252		—		373,252		—
U.S. government-sponsored enterprise securities		398,298		—		398,298		—
U.S. treasury securities		200,475		—		200,475		—
Restricted cash (money market funds)		1,471		1,471		—		—
Total	$	1,577,988	$	124,457	$	1,453,531	$	—