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Investments - Gross Unrealized Losses and Fair Values of Investments in an Unrealized Loss Position (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Mar. 31, 2023
--- | --- | ---
Fair Value |  |
Less than 12 months | $ 210,249 | $ 142,875
12 months or greater | 377,703 | 510,497
Total, fair value | 587,952 | 653,372
Gross Unrealized Losses |  |
Less than 12 months | (281) | (331)
12 months or greater | (11,706) | (18,593)
Total, unrealized losses | (11,987) | (18,924)
Asset-backed securities |  |
Fair Value |  |
Less than 12 months | 4,569 | 2,601
12 months or greater | 1,018 | 4,599
Total, fair value | 5,587 | 7,200
Gross Unrealized Losses |  |
Less than 12 months | (8) | (12)
12 months or greater | (4) | (59)
Total, unrealized losses | (12) | (71)
Certificates of deposit |  |
Fair Value |  |
Less than 12 months | 11,006 | 27,018
12 months or greater | 0 | 0
Total, fair value | 11,006 | 27,018
Gross Unrealized Losses |  |
Less than 12 months | (15) | (80)
12 months or greater | 0 | 0
Total, unrealized losses | (15) | (80)
Commercial paper |  |
Fair Value |  |
Less than 12 months | 96,131 | 70,681
12 months or greater | 0 | 0
Total, fair value | 96,131 | 70,681
Gross Unrealized Losses |  |
Less than 12 months | (44) | (126)
12 months or greater | 0 | 0
Total, unrealized losses | (44) | (126)
Corporate notes and bonds |  |
Fair Value |  |
Less than 12 months | 55,618 | 42,575
12 months or greater | 6,241 | 58,766
Total, fair value | 61,859 | 101,341
Gross Unrealized Losses |  |
Less than 12 months | (139) | (113)
12 months or greater | (127) | (665)
Total, unrealized losses | (266) | (778)
Sovereign bonds |  |
Fair Value |  |
Less than 12 months | 0 | 0
12 months or greater | 7,477 | 7,384
Total, fair value | 7,477 | 7,384
Gross Unrealized Losses |  |
Less than 12 months | 0 | 0
12 months or greater | (269) | (360)
Total, unrealized losses | (269) | (360)
U.S. government and agency securities |  |
Fair Value |  |
Less than 12 months | 42,925 | 0
12 months or greater | 362,967 | 439,748
Total, fair value | 405,892 | 439,748
Gross Unrealized Losses |  |
Less than 12 months | (75) | 0
12 months or greater | (11,306) | (17,509)
Total, unrealized losses | $ (11,381) | $ (17,509)

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