Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2015

Assets measured at fair value on a recurring basis

We measure the following major security types at fair value on a recurring basis. The following summary breaks down the fair-value hierarchy that we used to value each security at June 30, 2015 and December 31, 2014 (in thousands):

	At June 30, 2015		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	89,072	$	89,072	$	—	$	—
Corporate debt securities (2)		422,726		—		422,726		—
Debt securities issued by U.S. government agencies (2)		109,642		—		109,642		—
Debt securities issued by states of the United States and political subdivisions of the states (3)		121,845		—		121,845		—
Investment in Regulus Therapeutics Inc.		60,604		60,604		—		—
Total	$	803,889	$	149,676	$	654,213	$	—

	At December 31, 2014		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	104,680	$	104,680	$	—	$	—
Corporate debt securities (4)		372,002		—		372,002		—
Debt securities issued by U.S. government agencies (2)		109,855		—		109,855		—
Debt securities issued by the U.S. Treasury (5)		19,017		19,017		—		—
Debt securities issued by states of the United States and political subdivisions of the states (6)		105,033		—		105,033		—
Investment in Regulus Therapeutics Inc.		81,881		—		—		81,881
Total	$	792,468	$	123,697	$	586,890	$	81,881

(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)

$18.8 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.

(4)

$0.8 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.

(5)

$10 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments on our condensed consolidated balance sheet.

(6)

$9.3 million included in cash and cash equivalents on our condensed consolidated balance sheet, with the difference included in short-term investments 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 reconciliation of our investments measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the six months ended June 30, 2015 (in thousands):


Beginning balance of Level 3 investments (at December 31, 2014)	$	81,881
Total gain included in accumulated other comprehensive income (loss)		22,377
Transfers out of Level 3 investments		(104,258	)
Ending balance of Level 3 investments (at June 30, 2015)	$	—