Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2018

Investments Debt And Equity Securities [Abstract]

Schedule of Investments

The table below summarizes the Company’s investments (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		(Losses)			Fair Value
June 30, 2018
Cash equivalents:
Money market funds	$	41,909	$	—	$	—		$	41,909
Commercial paper securities		15,232		1		—			15,233
Total		57,141		1		—			57,142
Available-for-sale securities:
Commercial paper securities		396,958		110		(75	)		396,993
Corporate debt securities		98,834		—		(158	)		98,676
U.S. government-sponsored entity debt securities		18,556		—		(3	)		18,553
Total		514,348		110		(236	)		514,222
Total cash equivalents and available-for-sale securities	$	571,489	$	111	$	(236	)	$	571,364
December 31, 2017
Cash equivalents:
Money market funds	$	24,290	$	—	$	—		$	24,290
Commercial paper securities		4,595		—		—			4,595
Total		28,885		—		—			28,885
Available-for-sale securities:
Commercial paper securities		110,365		—		(118	)		110,247
Corporate debt securities		75,886		—		(131	)		75,755
U.S. government-sponsored entity debt securities		8,498		—		(6	)		8,492
Total		194,749		—		(255	)		194,494
Total cash equivalents and available-for-sale securities	$	223,634		—	$	(255	)	$	223,379