Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Measurements [Abstract]

Assets Measured at Fair Value on a Recurring Basis

The following tables present the major security types we held at June 30, 2019 and December 31, 2018 that we regularly measure and carry at fair value. At June 30, 2019 and December 31, 2018, our ProQR investment was subject to trading restrictions that extend through the fourth quarter of 2019; as a result, we included a lack of marketability discount in valuing this investment,  which is a Level 3 input. The amount we owned in ProQR did not change from December 31, 2018 to June 30, 2019. The tables below 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, 2019		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	167,789	$	167,789	$	—	$	—
Corporate debt securities (2)		1,337,957		—		1,337,957		—
Debt securities issued by U.S. government agencies (3)		265,241		—		265,241		—
Debt securities issued by the U.S. Treasury (4)		338,257		338,257		—		—
Debt securities issued by states of the U.S. and political subdivisions of the states (3)		70,631		—		70,631		—
Other municipal debt securities (3)		2,942		—		2,942		—
Investment in ProQR Therapeutics N.V. (5)		896		—		—		896
Total	$	2,183,713	$	506,046	$	1,676,771	$	896

	At December 31, 2018		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	146,281	$	146,281	$	—	$	—
Corporate debt securities (6)		1,252,960		—		1,252,960		—
Debt securities issued by U.S. government agencies (3)		276,612		—		276,612		—
Debt securities issued by the U.S. Treasury (7)		260,154		260,154		—		—
Debt securities issued by states of the U.S. and political subdivisions of the states (3)		79,942		—		79,942		—
Investment in ProQR Therapeutics N.V. (5)		1,349		—		—		1,349
Total	$	2,017,298	$	406,435	$	1,609,514	$	1,349

The following footnotes reference lines on our condensed consolidated balance sheet:

(1) Included in cash and cash equivalents.

(2) $4.0 million was included in cash and cash equivalents, with the difference included in short-term investments.

(3) Included in short-term investments.

(4) $21.6 million was included in cash and cash equivalents, with the difference included in short-term investments.

(5) Included in other current assets.

(6) $50.2 million was included in cash and cash equivalents, with the difference included in short-term investments.

(7) $14.2 million was included in cash and cash equivalents, with the difference included in short-term investments.