Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2016

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 valued each security with at June 30, 2016 and December 31, 2015 (in thousands):

	At June 30, 2016		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	68,737	$	68,737	$	—
Corporate debt securities (2)		371,197		—		371,197
Debt securities issued by U.S. government agencies (3)		76,734		—		76,734
Debt securities issued by the U.S. Treasury (2)		22,071		22,071		—
Debt securities issued by states of the U.S. and political subdivisions of the states (4)		117,697		—		117,697
Investment in Regulus Therapeutics Inc.		8,217		8,217		—
Total	$	664,653	$	99,025	$	565,628

	At December 31, 2015		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	88,902	$	88,902	$	—
Corporate debt securities (2)		438,426		—		438,426
Debt securities issued by U.S. government agencies (2)		89,253		—		89,253
Debt securities issued by the U.S. Treasury (2)		2,601		2,601		—
Debt securities issued by states of the U.S. and political subdivisions of the states (4)		127,656		—		127,656
Investment in Regulus Therapeutics Inc.		24,792		24,792		—
Total	$	771,630	$	116,295	$	655,335

(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)

At June 30, 2016, $16.0 million was 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)

At June 30, 2016 and December 31, 2015, $20.1 million and $7.5 million, respectively, were 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.