Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2012
			Fair Value Hierarchy
	Total		Level 1		Level 2		Level 3
	(in thousands)
Financial assets carried at fair value:
Cash equivalents:
Money market funds	$	149,094	$	149,094	$	—	$	—
U.S. Treasury securities		181,221		181,221		—		—
Marketable securities:
U.S. Treasury securities		114,055		114,055		—		—
Government-sponsored enterprise securities		371,158		371,158		—		—
Commercial paper		229,435		—		229,435		—
Corporate debt securities		54,625		—		54,625		—
Restricted cash		34,090		34,090		—		—
Total	$	1,133,678	$	849,618	$	284,060	$	—