Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2018

Assets Measured at Fair Value on a Recurring Basis

The following tables present the major security types we held at March 31, 2018 and December 31, 2017 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 March 31, 2018		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	138,350	$	138,350	$	—
Corporate debt securities (2)		556,338		—		556,338
Debt securities issued by U.S. government agencies (3)		150,297		—		150,297
Debt securities issued by the U.S. Treasury (3)		54,034		54,034		—
Debt securities issued by states of the U.S. and political subdivisions of the states (3)		83,392		—		83,392
Total	$	982,411	$	192,384	$	790,027

	At December 31, 2017		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	86,262	$	86,262	$	—
Corporate debt securities (3)		647,461		—		647,461
Debt securities issued by U.S. government agencies (3)		136,325		—		136,325
Debt securities issued by the U.S. Treasury (3)		30,818		30,818		—
Debt securities issued by states of the U.S. and political subdivisions of the states (4)		93,932		—		93,932
Total	$	994,798	$	117,080	$	877,718

(1)

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

(2)

At March 31, 2018, $14.6 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 December 31, 2017, $3.5 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.

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 three months ended March 31, 2017 (in thousands):


Beginning balance of Level 3 instruments at January 1, 2017	$	—
Value of the potential premium we would have received from Novartis at inception of the SPA (January 2017)		5,035
Recurring fair value adjustment during the three months ended March 31, 2017		(1,438	)
Ending balance of Level 3 instruments at March 31, 2017	$	3,597