Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2012

Fair Value of Financial Instruments

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

	Fair Value Measurements as of March 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	$	159,974	$	159,974	$	—	$	—
Government-sponsored enterprise securities		2,150		2,150		—		—
Commercial paper		4,250		—		4,250		—
Marketable securities:
U.S. Treasury securities		26,197		26,197		—		—
Government-sponsored enterprise securities		495,318		495,318		—		—
Commercial paper		145,447		—		145,447		—
Corporate debt securities		45,982		—		45,982		—
Restricted cash		34,090		34,090		—		—
Total	$	913,408	$	717,729	$	195,679	$	—