Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities

Marketable securities at September 30, 2018 consisted of the following (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Current:
Certificates of deposit	$	960	$	—	$	(6)	$	954
U.S Treasuries	244,818		—		(302)		244,516
Government securities	61,522		—		(163)		61,359
Corporate debt securities	206,948		—		(363)		206,585
Non-current:
Certificates of deposit	—		—		—		—
U.S Treasuries	21,860		—		(257)		21,603
Government securities	53,301		—		(253)		53,048
Corporate debt securities	134,632		—		(775)		133,857
Total marketable securities	$	724,041	$	—	$	(2,119)	$	721,922

Marketable securities at December 31, 2017 consisted of the following (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Current:
Certificates of deposit	$	8,081	$	—	$	(11)	$	8,070
U.S. Treasuries	113,852		—		(119)		113,733
Government securities	44,421		—		(57)		44,364
Corporate debt securities	155,222		—		(177)		155,045
Non-current:
Certificates of deposit	960		—		(8)		952
U.S. Treasuries	36,165		—		(311)		35,854
Government securities	23,992		—		(182)		23,810
Corporate debt securities	83,722		—		(524)		83,198
Total marketable securities	$	466,415	$	—	$	(1,389)	$	465,026