Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2013

Schedule of assets measured at fair value on a recurring basis

We break down the inputs used to measure fair value for these assets at June 30, 2013 and December 31, 2012 as follows (in thousands):

	At June 30, 2013		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	287,759	$	277,272	$	10,487	$	—
Corporate debt securities (2)	231,216		—		231,216		—
Debt securities issued by U.S. government agencies (2)	28,837		—		28,837		—
Debt securities issued by the U.S. Treasury (2)	13,381		13,381		—		—
Debt securities issued by states of the United States and political subdivisions of the states (2)	20,778		—		20,778		—
Investment in Regulus Therapeutics Inc.	62,190		—		—		62,190
Equity securities (3)	1,434		1,434		—		—
Total	$	645,595	$	292,087	$	291,318	$	62,190

	At December 31, 2012		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	105,496	$	101,496	$	4,000	$	—
Corporate debt securities (2)	193,507		—		193,507		—
Debt securities issued by U.S. government agencies (2)	18,108		—		18,108		—
Debt securities issued by the U.S. Treasury (2)	13,452		13,452		—		—
Debt securities issued by states of the United States and political subdivisions of the states (2)	24,897		—		24,897		—
Investment in Regulus Therapeutics Inc.	33,622		—		—		33,622
Equity securities (3)	4,874		4,146		—		728
Total	$	393,956	$	119,094	$	240,512	$	34,350

(1) Included in cash and cash equivalents on our condensed consolidated balance sheet.

(2) Included in short-term investments on our condensed consolidated balance sheet.

(3) Included in other current assets on our condensed consolidated balance sheet.

Summary of investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3)

The following is a summary of our investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the six months ended June 30, 2013 (in thousands):

	Investments Valued Using Level 3 Inputs
Balance at December 31, 2012	$	34,350
Total gains and losses:
Included in gain on investments	(1,163		)
Included in accumulated other comprehensive income (loss)	29,043
Cost basis of shares sold	(40		)
Balance at June 30, 2013	$	62,190

- Definition

Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).

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- Definition

Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset.

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