Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2017

Assets Measured at Fair Value on a Recurring Basis

The following tables present the major security types we held at June 30, 2017 and December 31, 2016 that are regularly measured and carried at fair value. The tables segregate each security type by the level within the fair value hierarchy of the valuation techniques we utilized to determine the respective securities’ fair value (in thousands):

	At June 30, 2017		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	113,466	$	113,466	$	—
Corporate debt securities (2)		527,684		—		527,684
Debt securities issued by U.S. government agencies (3)		82,100		—		82,100
Debt securities issued by the U.S. Treasury (4)		28,270		28,270		—
Debt securities issued by states of the U.S. and political subdivisions of the states (5)		93,039		—		93,039
Other municipal debt securities (3)		2,998		—		2,998
Total	$	847,557	$	141,736	$	705,821

	At December 31, 2016		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	54,137	$	54,137	$	—
Corporate debt securities (3)		396,221		—		396,221
Debt securities issued by U.S. government agencies (3)		55,179		—		55,179
Debt securities issued by the U.S. Treasury (3)		29,286		29,286		—
Debt securities issued by states of the U.S. and political subdivisions of the states (5)		109,111		—		109,111
Investment in Regulus Therapeutics Inc.		2,414		2,414		—
Total	$	646,348	$	85,837	$	560,511

(1)

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

(2)

At June 30, 2017, $7.5 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.

(3)

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

(4)

At June 30, 2017, $2.5 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.

(5)

At June 30, 2017 and December 31, 2016, $1.4 million and $9.3 million, respectively, 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.

Reconciliation of Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3)

The following is a reconciliation of the potential premium we would have received if Akcea had not completed its IPO, measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the six months ended June 30, 2017 (in thousands):

Beginning balance of Level 3 asset (at December 31, 2016)	$	—
Value of the potential premium we will receive from Novartis at inception of the SPA (January 2017)		5,035
Recurring fair value adjustment during the six months ended June 30, 2017		(1,438	)
Ending balance of Level 3 asset (at June 30, 2017)	$	3,597