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Investments - Summary of Investments (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
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Investments [Abstract] |  |  |
Amortized cost |  | $ 1,281,655 | $ 1,402,258
Gross unrealized gains |  | 1,276 | 1,607
Gross unrealized losses |  | (146) | (399)
Estimated fair value |  | 1,282,785 | 1,403,466
Amortized cost |  | 698,837 | 654,600
Gross unrealized gains |  | 2,333 | 984
Gross unrealized losses |  | (230) | (3,042)
Estimated fair value |  | 700,940 | 652,542
Amortized cost |  | 1,980,492 | 2,056,858
Gross unrealized gains |  | 3,609 | 2,591
Gross unrealized losses |  | (376) | (3,441)
Estimated fair value |  | 1,983,725 | 2,056,008
Amortized cost |  | 16,802 | 35,012
Gross unrealized gains |  | 54,435 | 25,027
Gross unrealized losses |  | (15,771) | (13,753)
Estimated fair value |  | 55,466 | 46,286
Amortized cost |  | 1,997,294 | 2,091,870
Gross unrealized gains |  | 58,044 | 27,618
Gross unrealized losses |  | (16,147) | (17,194)
Estimated fair value |  | 2,039,191 | 2,102,294
Corporate Debt Securities [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost | [1] | 639,937 | 593,810
Gross unrealized gains |  | 815 | 487
Gross unrealized losses |  | (69) | (240)
Estimated fair value |  | 640,683 | 594,057
Amortized cost |  | 415,818 | 439,561
Gross unrealized gains |  | 1,688 | 723
Gross unrealized losses |  | (121) | (2,275)
Estimated fair value |  | 417,385 | 438,009
Debt Securities Issued by U.S. Government Agencies [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost |  | 73,905 | 143,647
Gross unrealized gains |  | 66 | 287
Gross unrealized losses |  | (16) | (39)
Estimated fair value |  | 73,955 | 143,895
Amortized cost |  | 76,548 | 65,255
Gross unrealized gains |  | 147 | 137
Gross unrealized losses |  | (60) | (289)
Estimated fair value |  | 76,635 | 65,103
Debt Securities Issued by the U.S. Treasury [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost | [1] | 562,662 | 657,285
Gross unrealized gains |  | 384 | 825
Gross unrealized losses |  | (61) | (120)
Estimated fair value |  | 562,985 | 657,990
Amortized cost |  | 204,656 | 149,086
Gross unrealized gains |  | 493 | 124
Gross unrealized losses |  | (49) | (476)
Estimated fair value |  | 205,100 | 148,734
Debt Securities Issued by States of the U.S. and Political Subdivisions of the States [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost |  | 5,151 | 7,516
Gross unrealized gains |  | 11 | 8
Gross unrealized losses |  | 0 | 0
Estimated fair value |  | 5,162 | 7,524
Amortized cost |  | 1,117 |
Gross unrealized gains |  | 5 |
Gross unrealized losses |  | 0 |
Estimated fair value |  | 1,122 |
Other Municipal Debt Securities [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost |  | 698 | 698
Gross unrealized gains |  | 0 | 0
Gross unrealized losses |  | 0 | (2)
Estimated fair value |  | 698 | 696
Publicly Traded Equity Securities [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost | [2] | 11,897 | 11,897
Gross unrealized gains |  | 40 | 26
Gross unrealized losses |  | (8,681) | (6,660)
Estimated fair value |  | 3,256 | 5,263
Privately Held Equity Securities [Member] |  |  |
Investments [Abstract] |  |  |
Amortized cost | [3] | 4,905 | 23,115
Gross unrealized gains |  | 54,395 | 25,001
Gross unrealized losses |  | (7,090) | (7,093)
Estimated fair value |  | $ 52,210 | $ 41,023
[1] | Includes investments classified as cash equivalents in our condensed consolidated balance sheets.
[2] | Our publicly traded equity securities are included in other current assets. We recognize publicly traded equity securities at fair value. In the nine months ended September 30, 2025, we recorded a $2.0 million net unrealized loss in our condensed consolidated statements of operations related to changes in the fair value of our investments in publicly traded companies.
[3] | Our privately held equity securities are included in deposits and other assets. We recognize our privately held equity securities at cost minus impairments, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer, which are Level 3 inputs. In the nine months ended September 30, 2025, the amortized cost of our privately held equity securities increased $11.2 million. In the third quarter of 2025, we recorded a $29.4 million unrealized gain related to our investment in a privately held company due to an observable price change in an orderly transaction for a similar investment of the investee. This increase was partially offset by a loss of $18.2 million related to an impairment of our investment in another privately held company that we recorded in the second quarter of 2025.

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