Cash and Cash Equivalents and Investments (Tables)

9 Months Ended

Sep. 30, 2015

Cash and Cash Equivalents and Investments [Abstract]

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

	As of September 30, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	61,674	$	—	$	—		$	61,674
Securities maturing within one year:
Certificates of deposit	553		—		—			553
U.S. treasury securities	191,231		59		—			191,290
Corporate debt securities	2,906		—		(1		)	2,905
Total short-term investments	$	194,690	$	59	$	(1	)	$	194,748
Total cash and cash equivalents and investments	$	256,364	$	59	$	(1	)	$	256,422
	As of December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	137,266	$	—	$	—		$	137,266
Securities maturing within one year:
Certificates of deposit	552		—		—			552
U.S. treasury securities	201,584		3		(66		)	201,521
Total short-term investments	$	202,136	$	3	$	(66	)	$	202,073
Total cash and cash equivalents and investments	$	339,402	$	3	$	(66	)	$	339,339