Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Cash Equivalents and Available-for-Sale Securities

The table below summarizes the Company’s cash equivalents and available-for-sale securities (in thousands):

			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		(Losses)			Fair Value
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
December 31, 2016
Cash equivalents:
Money market funds	$	18,992	$	—	$	—		$	18,992
Total		18,992		—		—			18,992
Available-for-sale securities:
Commercial paper securities		23,112		73		—			23,185
Corporate debt securities		10,005		—		(1	)		10,004
U.S. government-sponsored entity debt securities		87,307		3		(25	)		87,285
Total		120,424		76		(26	)		120,474
Total cash equivalents and available-for-sale securities	$	139,416	$	76	$	(26	)	$	139,466