Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Disclosures [Abstract]

Financial assets subject to fair value measurements (excluding restricted cash and cash equivalents (Alios))

The following table sets forth the Company’s financial assets (excluding Alios’ cash equivalents) subject to fair value measurements:

	Fair Value Measurements as of December 31, 2012
			Fair Value Hierarchy
	Total		Level 1		Level 2		Level 3
	(in thousands)
Financial assets carried at fair value:
Cash equivalents:
Money market funds	$	268,463	$	268,463	$	—	$	—
Marketable securities:
U.S. Treasury securities	111,350		111,350		—		—
Government-sponsored enterprise securities	440,225		440,225		—		—
Commercial paper	225,449		—		225,449		—
Corporate debt securities	54,784		—		54,784		—
Restricted cash	31,934		31,934		—		—
Total	$	1,132,205	$	851,972	$	280,233	$	—