INVESTMENTS (Tables)

6 Months Ended

Jun. 30, 2019

Investments, Debt and Equity Securities [Abstract]

Schedule of cash, cash equivalents and short-term investments

The short-term investments are classified as available-for-sale securities. The cash, cash equivalents and short-term investments at June 30, 2019 and December 31, 2018 were as follows:

	June 30, 2019
	Amortized Cost			Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	49,734		$	—	$	—		$	49,734
Money market funds	4,048			—		—			4,048
Certificates of deposit	149,074			39		(5		)	149,108
Government debt securities	149,683			474		(13		)	150,144
Corporate debt securities	256,457			1,124		(27		)	257,554
Total	608,996			1,637		(45		)	610,588
Less amounts classified as cash and cash equivalents	(53,782		)	—		—			(53,782		)
Short-term investments	$	555,214		$	1,637	$	(45	)	$	556,806

	December 31, 2018
	Amortized Cost			Unrealized Gains		Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	55,501		$	—	$	—		$	55,501
Money market funds	1,265			—		—			1,265
Certificates of deposit	95,080			1		(43		)	95,038
Government debt securities	100,449			92		(63		)	100,478
Corporate debt securities	186,571			27		(390		)	186,208
Total	438,866			120		(496		)	438,490
Less amounts classified as cash and cash equivalents	(56,766		)	—		—			(56,766		)
Short-term investments	$	382,100		$	120	$	(496	)	$	381,724

Schedule of contractual maturities of short-term investments

The contractual maturities of short-term investments at June 30, 2019 and December 31, 2018 were as follows:

	June 30, 2019				December 31, 2018
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(in thousands)
Due in less than one year	$	359,796	$	360,247	$	281,303	$	280,959
Due in one to three years	195,418		196,559		100,797		100,765
	$	555,214	$	556,806	$	382,100	$	381,724