Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Marketable Securities [Abstract]

Amortized Cost And Fair Value Of Marketable Securities

As of December 31, 2017		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds	$	140,969	$	96	$	(179)	$	140,886
Certificates of deposit		58,510		-		-		58,510
Commercial paper		29,171		-		-		29,171
Asset backed securities		22,206		4		(43)		22,167
U.S. government bonds		15,619		11		(19)		15,611
Agency bonds		10,990		9		(52)		10,947
Treasury bills		6,964		-		(1)		6,963
Total marketable securities	$	284,429	$	120	$	(294)	$	284,255
As of December 31, 2016		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Corporate bonds	$	130,833	$	40	$	(102)	$	130,771
Certificates of deposit		40,400		-		-		40,400
Asset backed securities		27,290		25		-		27,315
Commercial paper		20,228		-		-		20,228
U.S. government bonds		12,244		1		(14)		12,231
Agency bonds		4,600		4		-		4,604
Municipal bonds		1,400		-		-		1,400
Total marketable securities	$	236,995	$	70	$	(116)	$	236,949

Contractual Maturities Of Marketable Securities

As of December 31, 2017		Amortized Cost		Fair Value
Due in one year or less	$	175,849	$	175,780
Due after one through three years		108,580		108,475
	$	284,429	$	284,255