Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of amortized cost, unrealized gain and loss and the fair value of available-for-sale securities

The following table is a summary of amortized cost, unrealized gain and loss, and the fair value of available-for-sale securities as of December 31, 2017 and 2016 (in thousands):

	December 31, 2017
			Gross Unrealized		Gross Unrealized
	Amortized Cost		Gains		Losses			Fair Value
Investments:
Corporate debt	$	23,507	$	—	$	(36	)	$	23,471
U.S. Treasury notes	61,777		—		(131		)	61,646
Total	$	85,284	$	—	$	(167	)	$	85,117
Reported as:
Short-term investments	$	82,280			$	(154	)	$	82,126
Long-term investments	3,004				(13		)	2,991
Total	$	85,284	$	—	$	(167	)	$	85,117

	December 31, 2016
			Gross Unrealized		Gross Unrealized
	Amortized Cost		Gains		Losses			Fair Value
Investments:
Corporate debt	$	51,354	$	—	$	(121	)	$	51,233
U.S. Treasury notes	61,048		5		(77		)	60,976
Total	$	112,402	$	5	$	(198	)	$	112,209
Reported as:
Short-term investments	$	90,050	$	1	$	(134	)	$	89,917
Long-term investments	22,352		4		(64		)	22,292
Total	$	112,402	$	5	$	(198	)	$	112,209