Fair Value Measurements (Details) (USD $)	Jun. 30, 2013
Financial assets carried at fair value:
Cash equivalents (Alios)	$ 56,500,000
Recurring basis | Total
Financial assets carried at fair value:
Total	1,200,601,000
Recurring basis | Total | Money market funds
Financial assets carried at fair value:
Cash equivalents:	300,472,000
Recurring basis | Total | U.S. Treasury securities
Financial assets carried at fair value:
Cash equivalents:	680,000
Marketable securities:	3,050,000
Recurring basis | Total | Government-sponsored enterprise securities
Financial assets carried at fair value:
Marketable securities:	598,411,000
Recurring basis | Total | Commercial paper
Financial assets carried at fair value:
Marketable securities:	192,878,000
Recurring basis | Total | Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	105,110,000
Recurring basis | Level 1
Financial assets carried at fair value:
Total	902,613,000
Recurring basis | Level 1 | Money market funds
Financial assets carried at fair value:
Cash equivalents:	300,472,000
Recurring basis | Level 1 | U.S. Treasury securities
Financial assets carried at fair value:
Cash equivalents:	680,000
Marketable securities:	3,050,000
Recurring basis | Level 1 | Government-sponsored enterprise securities
Financial assets carried at fair value:
Marketable securities:	598,411,000
Recurring basis | Level 1 | Commercial paper
Financial assets carried at fair value:
Marketable securities:	0
Recurring basis | Level 1 | Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	0
Recurring basis | Level 2
Financial assets carried at fair value:
Total	297,988,000
Recurring basis | Level 2 | Money market funds
Financial assets carried at fair value:
Cash equivalents:	0
Recurring basis | Level 2 | U.S. Treasury securities
Financial assets carried at fair value:
Cash equivalents:	0
Marketable securities:	0
Recurring basis | Level 2 | Government-sponsored enterprise securities
Financial assets carried at fair value:
Marketable securities:	0
Recurring basis | Level 2 | Commercial paper
Financial assets carried at fair value:
Marketable securities:	192,878,000
Recurring basis | Level 2 | Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	105,110,000
Recurring basis | Level 3
Financial assets carried at fair value:
Total	0
Recurring basis | Level 3 | Money market funds
Financial assets carried at fair value:
Cash equivalents:	0
Recurring basis | Level 3 | U.S. Treasury securities
Financial assets carried at fair value:
Cash equivalents:	0
Marketable securities:	0
Recurring basis | Level 3 | Government-sponsored enterprise securities
Financial assets carried at fair value:
Marketable securities:	0
Recurring basis | Level 3 | Commercial paper
Financial assets carried at fair value:
Marketable securities:	0
Recurring basis | Level 3 | Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	$ 0