Cash and Cash Equivalents and Investments (Tables)

3 Months Ended

Mar. 31, 2015

Cash and Cash Equivalents and Investments [Abstract]

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

	As of March 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	41,960	$	—	$	—		$	41,960
Securities maturing within one year:
Certificates of deposit	552		—		—			552
U.S. treasury securities	272,562		50		(27		)	272,585
Total short-term investments	$	273,114	$	50	$	(27	)	$	273,137
Total cash and cash equivalents and investments	$	315,074	$	50	$	(27	)	$	315,097
	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