Fair Value Measurements (Details) (USD $)	Sep. 30, 2013
Financial assets carried at fair value:
Cash equivalents (Alios)	$ 48,700,000
Recurring basis | Total
Financial assets carried at fair value:
Total	1,151,345,000
Recurring basis | Total | Money market funds
Financial assets carried at fair value:
Cash equivalents:	308,981,000
Recurring basis | Total | Government-sponsored enterprise securities
Financial assets carried at fair value:
Cash equivalents:	2,895,000
Marketable securities:	555,527,000
Recurring basis | Total | Commercial paper
Financial assets carried at fair value:
Marketable securities:	125,264,000
Recurring basis | Total | Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	158,678,000
Recurring basis | Level 1
Financial assets carried at fair value:
Total	867,403,000
Recurring basis | Level 1 | Money market funds
Financial assets carried at fair value:
Cash equivalents:	308,981,000
Recurring basis | Level 1 | Government-sponsored enterprise securities
Financial assets carried at fair value:
Cash equivalents:	2,895,000
Marketable securities:	555,527,000
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	283,942,000
Recurring basis | Level 2 | Money market funds
Financial assets carried at fair value:
Cash equivalents:	0
Recurring basis | Level 2 | Government-sponsored enterprise securities
Financial assets carried at fair value:
Cash equivalents:	0
Marketable securities:	0
Recurring basis | Level 2 | Commercial paper
Financial assets carried at fair value:
Marketable securities:	125,264,000
Recurring basis | Level 2 | Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	158,678,000
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 | Government-sponsored enterprise securities
Financial assets carried at fair value:
Cash equivalents:	0
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