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Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments

Summary of fair value and unrealized gains (losses) position of available for sale securities

					Gross			Gross
		Amortized			Unrealized			Unrealized			Estimated
		Cost			Gains			Losses			Fair Value
		(in thousands)
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


December 31, 2016
U.S. treasuries		$	40,013		$	—		$	(5	)	$	40,008
Government agency securities		10,020			—			(8		)	10,012
Corporate debt		13,780			—			(7		)	13,773
Commercial paper		2,994			—			—			2,994

Total		$	66,807		$	—		$	(20	)	$	66,787

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

		December 31, 2017						December 31, 2016
					Gross						Gross
		Estimated			Unrealized			Estimated			Unrealized
		Fair Value			Losses			Fair Value			Losses
		(in thousands)
U.S. treasuries		$	33,895		$	(19	)	$	20,002		$	(5	)
Government agency securities		—			—			10,012			(8		)
Corporate debt		10,886			(8		)	13,773			(7		)

Total		$	44,781		$	(27	)	$	43,787		$	(20	)