Cash and Cash Equivalents and Investments (Tables)

9 Months Ended

Sep. 30, 2019

Cash and Cash Equivalents and Investments [Abstract]

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

	As of September 30, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	170,203	$	—	$	—		$	170,203
Securities maturing within one year:
U.S. treasury securities	126,065		44		(8		)	126,101
Total short-term investments	$	126,065	$	44	$	(8	)	$	126,101
Total cash and cash equivalents and investments	$	296,268	$	44	$	(8	)	$	296,304
	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