Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Marketable securities, gross unrealized gains/losses

June 30, 2018	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate notes and bonds	$	13,809	$	—	$	(8	)	$	13,801
U.S. government and agency securities	3,484		—		(1		)	3,483
Commercial paper	9,074		—		—			9,074
Total	$	26,367	$	—	$	(9	)	$	26,358
December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate notes and bonds	$	26,303	$	—	$	(25	)	$	26,278
U.S. government and agency securities	11,981		—		(5		)	11,976
Commercial paper	6,982		—		—			6,982
Total	$	45,266	$	—	$	(30	)	$	45,236