Fair Value Measurements (Details) (USD $)	Mar. 31, 2013
Financial assets carried at fair value:
Cash equivalents (Alios)	$ 60,100,000
Recurring basis \| Total
Financial assets carried at fair value:
Restricted cash	31,934,000
Total	1,132,608,000
Recurring basis \| Total \| Money market funds
Financial assets carried at fair value:
Cash equivalents:	201,831,000
Recurring basis \| Total \| U.S. Treasury securities
Financial assets carried at fair value:
Marketable securities:	13,205,000
Recurring basis \| Total \| Government-sponsored enterprise securities
Financial assets carried at fair value:
Cash equivalents:	38,588,000
Marketable securities:	550,478,000
Recurring basis \| Total \| Commercial paper
Financial assets carried at fair value:
Marketable securities:	216,942,000
Recurring basis \| Total \| Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	79,630,000
Recurring basis \| Level 1
Financial assets carried at fair value:
Restricted cash	31,934,000
Total	836,036,000
Recurring basis \| Level 1 \| Money market funds
Financial assets carried at fair value:
Cash equivalents:	201,831,000
Recurring basis \| Level 1 \| U.S. Treasury securities
Financial assets carried at fair value:
Marketable securities:	13,205,000
Recurring basis \| Level 1 \| Government-sponsored enterprise securities
Financial assets carried at fair value:
Cash equivalents:	38,588,000
Marketable securities:	550,478,000
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:
Restricted cash	0
Total	296,572,000
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:
Marketable securities:	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:	216,942,000
Recurring basis \| Level 2 \| Corporate debt securities
Financial assets carried at fair value:
Marketable securities:	79,630,000
Recurring basis \| Level 3
Financial assets carried at fair value:
Restricted cash	0
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:
Marketable securities:	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

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

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- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

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