Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2013

Summary of Significant Accounting Policies Investments in Marketable Securities [Abstract]

Marketable Securities

Short-term marketable securities for the periods presented were comprised of the following (in thousands):

	June 30, 2013
Security Type	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. government fixed income securities(1)	$	171,881	$	31	$	(696	)	$	171,216
Total short-term investments	$	171,881	$	31	$	(696	)	$	171,216

⁽¹⁾ Maturity dates ranging from 2013 to 2014.

	December 31, 2012
Security Type	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. government fixed income securities	$	87,394	$	20	$	(411	)	$	87,003
Equity securities of certain technology companies	3,254		—		(782		)	2,472
Total short-term investments	$	90,648	$	20	$	(1,193	)	$	89,475