Cash and Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2012

Cash and Cash Equivalents and Investments [Abstract]

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

	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

	As of December 31, 2011
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	186,309	$	—	$	—		$	186,309
Securities maturing within one year:
Certificates of deposit	548		—		—			548
U.S. treasury securities	94,814		24		(3		)	94,835
Total short-term investments	$	95,362	$	24	$	(3	)	$	95,383
Total cash and cash equivalents and investments	$	281,671	$	24	$	(3	)	$	281,692