Investments - Schedule of Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 17,579,376	$ 17,589,342
Corporates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	14,151,002	14,171,518
States, municipalities, and political subdivisions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	2,884,630	2,880,626
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	413,104	395,225
Significant Unobservable Inputs (Level 3) | Corporates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	310,503	309,324
Significant Unobservable Inputs (Level 3) | Corporates | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	310,503
Significant Unobservable Inputs (Level 3) | States, municipalities, and political subdivisions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	2,977	$ 0
Significant Unobservable Inputs (Level 3) | States, municipalities, and political subdivisions | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	2,977
Significant Unobservable Inputs (Level 3) | Asset- backed Securities | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 99,624