Cash and Cash Equivalents and Investments (Tables)

3 Months Ended

Mar. 31, 2019

Cash and Cash Equivalents and Investments [Abstract]

Schedule of Cash, Cash Equivalents and Short-term Investments [Table Text Block]

	As of March 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	45,778	$	—	$	—		$	45,778
Securities maturing within one year:
U.S. treasury securities	87,334		35		(2		)	87,367
Corporate debt securities	—		—		—			—
Total short-term investments	$	87,334	$	35	$	(2	)	$	87,367
Total cash and cash equivalents and investments	$	133,112	$	35	$	(2	)	$	133,145
	As of December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	80,386	$	—	$	—		$	80,386
Securities maturing within one year:
U.S. treasury securities	73,983		—		(9		)	73,974
Corporate debt securities	5,695		—		(3		)	5,692
Total short-term investments	$	79,678	$	—	$	(12	)	$	79,666
Total cash and cash equivalents and investments	$	160,064	$	—	$	(12	)	$	160,052