Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 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 March 31, 2019 and December 31, 2018 that we regularly measure and carry at fair value. At March 31, 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 March 31, 2019. 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, 2019		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents (1)	$	146,542	$	146,542	$	—	$	—
Corporate debt securities (2)		1,231,154		—		1,231,154		—
Debt securities issued by U.S. government agencies (3)		245,308		—		245,308		—
Debt securities issued by the U.S. Treasury (4)		361,997		361,997		—		—
Debt securities issued by states of the U.S. and political subdivisions of the states (3)		78,663		—		78,663		—
Other municipal debt securities (3)		2,932		—		2,932		—
Investment in ProQR Therapeutics N.V. (5)		968		—		—		968
Total	$	2,067,564	$	508,539	$	1,558,057	$	968

	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

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

(2) $27.1 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) $15.0 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.

(5) Included in other current assets on our condensed consolidated balance sheet.

(6) $50.2 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.

(7) $14.2 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.