Cash and Cash Equivalents and Investments

12 Months Ended

Dec. 31, 2012

Cash and Cash Equivalents and Investments [Abstract]

Cash and Cash Equivalents and Investments

Cash and Cash Equivalents and Investments

The fair value of cash and cash equivalents and investments held at December 31, 2012 and 2011 are as follows:

	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

There were no realized gains or losses for the year ended December 31, 2012, no realized gains or losses for the year ended December 31, 2011, and no realized gains or losses for the year ended December 31, 2010.