Cash and Cash Equivalents and Investments (Tables)

6 Months Ended

Jun. 30, 2013

Cash and Cash Equivalents and Investments [Abstract]

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

	As of June 30, 2013
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash and cash equivalents	$	23,254	$	—	$	—		$	23,254
Securities maturing within one year:
Certificates of deposit	551		—		—			551
U.S. treasury securities	151,542		31		—			151,573
Total short-term investments	$	152,093	$	31	$	—		$	152,124
Total cash and cash equivalents and investments	$	175,347	$	31	$	—		$	175,378
	As of December 31, 2012
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	30,423	$	—	$	—		$	30,423
Securities maturing within one year:
Certificates of deposit	551		—		—			551
U.S. treasury securities	192,211		24		(1		)	192,234
Total short-term investments	$	192,762	$	24	$	(1	)	$	192,785
Total cash and cash equivalents and investments	$	223,185	$	24	$	(1	)	$	223,208