Fair Value Measurements

12 Months Ended

Dec. 31, 2012

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

Fair Value Measurements

The fair value of the Company’s financial assets and liabilities reflects the Company’s estimate of amounts that it would have received in connection with the sale of the assets or paid in connection with the transfer of the liabilities in an orderly transaction between market participants at the measurement date. In connection with measuring the fair value of its assets and liabilities, the Company seeks to maximize the use of observable inputs (market data obtained from sources independent from the Company) and to minimize the use of unobservable inputs (the Company’s assumptions about how market participants would price assets and liabilities). The following fair value hierarchy is used to classify assets and liabilities based on the observable inputs and unobservable inputs used in order to value the assets and liabilities:

Level 1:	Quoted prices in active markets for identical assets or liabilities. An active market for an asset or liability is a market in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis.
Level 2:	Observable inputs other than Level 1 inputs. Examples of Level 2 inputs include quoted prices in active markets for similar assets or liabilities and quoted prices for identical assets or liabilities in markets that are not active.
Level 3:	Unobservable inputs based on the Company’s assessment of the assumptions that market participants would use in pricing the asset or liability.

The Company’s investment strategy is focused on capital preservation. The Company invests in instruments that meet the credit quality standards outlined in the Company’s investment policy. This policy also limits the amount of credit exposure to any one issue or type of instrument. As of December 31, 2012, the Company’s investments were in a money market fund, short-term U.S. Treasury securities, short-term government-sponsored enterprise securities, corporate debt securities and commercial paper.

As of December 31, 2012, all of the Company’s financial assets that were subject to fair value measurements were valued using observable inputs. The Company’s financial assets valued based on Level 1 inputs consisted of a money market fund, U.S. Treasury securities and government-sponsored enterprise securities. The Company’s financial assets valued based on Level 2 inputs consisted of corporate debt securities and commercial paper, which consist of investments in highly-rated investment-grade corporations. During 2012, 2011 and 2010, the Company did not record an other-than-temporary impairment charge related to its financial assets. The Company’s noncontrolling interest (Alios) includes the fair value of the contingent milestone and royalty payments, which is valued based on Level 3 inputs. Please refer to Note B, "Collaborative Arrangements," for further information.

The following table sets forth the Company’s financial assets (excluding Alios’ cash equivalents) subject to fair value measurements:

	Fair Value Measurements as of December 31, 2012
			Fair Value Hierarchy
	Total		Level 1		Level 2		Level 3
	(in thousands)
Financial assets carried at fair value:
Cash equivalents:
Money market funds	$	268,463	$	268,463	$	—	$	—
Marketable securities:
U.S. Treasury securities	111,350		111,350		—		—
Government-sponsored enterprise securities	440,225		440,225		—		—
Commercial paper	225,449		—		225,449		—
Corporate debt securities	54,784		—		54,784		—
Restricted cash	31,934		31,934		—		—
Total	$	1,132,205	$	851,972	$	280,233	$	—

Alios’ cash equivalents of $68.7 million as of December 31, 2012 consisted of money market funds, which are valued based on Level 1 inputs.

As of December 31, 2012, the Company had $400.0 million in aggregate principal amount of 3.35% convertible senior subordinated notes due 2015 (the “2015 Notes”) on its consolidated balance sheet. As of December 31, 2012, these 2015 Notes had a fair value of approximately $444 million based on Level 2 inputs.