Fair Value Measurements (Tables)

3 Months Ended

Jun. 30, 2013

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 June 30, 2013
			Fair Value Hierarchy
	Total		Level 1		Level 2		Level 3
	(in thousands)
Financial assets carried at fair value:
Cash equivalents:
Money market funds	$	300,472	$	300,472	$	—	$	—
U.S. Treasury securities	680		680		—		—
Marketable securities:
U.S. Treasury securities	3,050		3,050		—		—
Government-sponsored enterprise securities	598,411		598,411		—		—
Commercial paper	192,878		—		192,878		—
Corporate debt securities	105,110		—		105,110		—
Total	$	1,200,601	$	902,613	$	297,988	$	—