Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2021

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, 2021 and December 31, 2020 that we regularly measure and carry at fair value. As of June 30, 2021 and December 31, 2020, we did not have any investments that we valued using Level 3 inputs. The following 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, 2021		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	461,711	$	461,711	$	—
Corporate debt securities (2)		857,234		—		857,234
Debt securities issued by U.S. government agencies (2)		137,265		—		137,265
Debt securities issued by the U.S. Treasury (2)		261,742		261,742		—
Debt securities issued by states of the U.S. and political subdivisions of the states (3)		232,752		—		232,752
Other municipal debt securities (2)		11,258		—		11,258
Investment in ProQR Therapeutics N.V. (4)		3,261		3,261		—
Total	$	1,965,223	$	726,714	$	1,238,509

	At December 31, 2020		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)
Cash equivalents (1)	$	221,125	$	221,125	$	—
Corporate debt securities (5)		846,315		—		846,315
Debt securities issued by U.S. government agencies (2)		174,861		—		174,861
Debt securities issued by the U.S. Treasury (6)		358,497		358,497		—
Debt securities issued by states of the U.S. and political subdivisions of the states (2)		136,309		—		136,309
Other municipal debt securities (2)		6,225		—		6,225
Investment in ProQR Therapeutics N.V. (4)		2,031		2,031		—
Total	$	1,745,363	$	581,653	$	1,163,710

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

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

(2) Included in short-term investments.

(3) $6.1 million was included in cash and cash equivalents, with the difference included in short-term investments.

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

(5) $10.0 million was included in cash and cash equivalents, with the difference included in short-term investments.

(6) $17.5 million 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.