Investments (Tables)

12 Months Ended

Dec. 31, 2018

Investments

Schedule of amortized cost and fair value of available-for-sale securities

			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
	Cost		Gains		Losses		Fair Value
	(in thousands)
December 31, 2018
U.S. treasuries	$	37,191	$	—	$	(7)	$	37,184
Corporate debt		8,525		—		(9)		8,516
Commercial paper		2,489		—		—		2,489
Total	$	48,205	$	—	$	(16)	$	48,189
December 31, 2017
U.S. treasuries	$	33,914	$	—	$	(19)	$	33,895
Corporate debt		10,894		—		(8)		10,886
Commercial paper		2,999		—		—		2,999
Total	$	47,807	$	—	$	(27)	$	47,780

Schedule of fair value and unrealized losses of available-for-sale securities in a loss position

	December 31, 2018				December 31, 2017
			Gross				Gross
	Estimated		Unrealized		Estimated		Unrealized
	Fair Value		Losses		Fair Value		Losses
	(in thousands)
U.S. treasuries	$	37,184	$	(7)	$	33,895	$	(19)
Corporate debt		8,516		(9)		10,886		(8)
Total	$	45,700	$	(16)	$	44,781	$	(27)