Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

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
	$	466,415	$	—	$	(1,389	)	$	465,026

Marketable securities at December 31, 2016 consisted of the following (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	11,280	$	2	$	(3	)	$	11,279
U.S. Treasuries	141,678		2		(62		)	141,618
Government securities	19,533		—		(23		)	19,510
Corporate debt securities	208,285		3		(135		)	208,153
Non-current:
Certificates of deposit	7,600		6		(13		)	7,593
Government securities	4,499		—		(21		)	4,478
Corporate debt securities	20,248		—		(69		)	20,179
	$	413,123	$	13	$	(326	)	$	412,810