Fair Value of Financial Instruments and Non-Financial Assets (Tables)

6 Months Ended

Jun. 30, 2012

Fair Value Disclosures [Abstract]

Schedule of Fair Value - Assets Measured on Recurring Basis

The following tables set forth by level within the fair value hierarchy the Company's assets and liabilities that were recorded at fair value as of June 30, 2012 and December 31, 2011 (in thousands). As required by the guidance for fair value measurements, financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Thus, assets and liabilities categorized as Level 3 may be measured at fair value using inputs that are observable (Levels 1 and 2) and unobservable (Level 3). Management's assessment of the significance of a particular input to the fair value measurement requires judgment, which may affect the valuation of assets and liabilities and their placement within the fair value hierarchy levels.

	At Fair Value as of June 30, 2012
	Level 1		Level 2		Level 3		Total
Assets:
Money market funds	$	—	$	126,634	$	—	$	126,634
Commercial paper	—		85,468		—		85,468
U.S. government or government agency securities	—		127,231		—		127,231
Total	$	—	$	339,333	$	—	$	339,333

	At Fair Value as of December 31, 2011
	Level 1		Level 2		Level 3		Total
Assets:
Money market funds	$	—	$	224,383	$	—	$	224,383
Commercial paper	—		165,202		—		165,202
U.S. government or government agency securities	—		293,610		—		293,610
Total	$	—	$	683,195	$	—	$	683,195

Available-for-sale Securities

Available-for-sale securities were comprised as follows as of June 30, 2012 and December 31, 2011 (in thousands):

	As of June 30, 2012
	Cost		Fair Value
Money market funds	$	126,634	$	126,634
Commercial paper	85,469		85,468
U.S. government or government agency securities	127,227		127,231
	$	339,330	$	339,333

	As of December 31, 2011
	Cost		Fair Value
Money market funds	$	224,383	$	224,383
Commercial paper	165,201		165,202
U.S. government or government agency securities	293,626		293,610
	$	683,210	$	683,195