Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments [Abstract]

Available-for-sale Securities

At December 31, 2017 and 2016, the estimated fair value of short-term and long-term investments classified as available for sale are as follows (in thousands):

	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments
Corporate debt securities	$	54,911	$	3	$	(52	)	$	54,862
Agency securities	10,781		—		(14		)	10,767
Commercial paper	101,546		—		—			101,546
U.S. Government securities	10,857		—		(11		)	10,846
Total short-term investments	$	178,095	$	3	$	(77	)	$	178,021
Long-term investments
Corporate debt securities	$	6,287	$	—	$	(25	)	$	6,262
Agency securities	2,000		—		(17		)	1,983
U.S. Government securities	998		—		(1		)	997
Total long-term investments	$	9,285	$	—	$	(43	)	$	9,242

	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments
Corporate debt securities	$	13,371	$	2	$	(12	)	$	13,361
Agency securities	7,957		6		—			7,963
Commercial paper	1,727		—		—			1,727
U.S. Government securities	3,298		3		—			3,301
Total short-term investments	$	26,353	$	11	$	(12	)	$	26,352
Long-term investments
Corporate debt securities	$	6,208	$	1	$	(20	)	$	6,189
Agency securities	5,359		—		(20		)	5,339
U.S. Government securities	2,956		1		(6		)	2,951
Total long-term investments	$	14,523	$	2	$	(46	)	$	14,479

Investments Classified by Contractual Maturity Date

The following table summarizes the contractual maturities of the Company's investments as of December 31, 2017 and 2016 (in thousands):

	December 31,
	2017		2016
One year or less	$	178,021	$	26,352
One year through three years	9,242		14,479
	$	187,263	$	40,831