Investments - Cost and Fair Value, Net of Credit Loss Allowance, of Fixed Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Available-for-sale securities:
Amortized cost	$ 1,363,228
Estimated fair value	1,364,828
Held-to-maturity securities:
Amortized cost	1,368,061	$ 1,070,789
Gross unrealized gains	17,455	6,907
Gross unrealized losses	15,825	29,147
Estimated fair value	1,369,691	1,048,549
Fair value of securities lent	64,500
Corporate debt securities
Available-for-sale securities:
Amortized cost	834,885	647,861
Gross unrealized gains	12,779	4,767
Gross unrealized losses	3,185	8,685
Estimated fair value	844,479	643,943
Held-to-maturity securities:
Fair value of securities lent		7,300
Collateralized debt obligations
Available-for-sale securities:
Amortized cost	133,224	114,142
Gross unrealized gains	207	372
Gross unrealized losses	164	387
Estimated fair value	133,267	114,127
Commercial mortgage-backed securities
Available-for-sale securities:
Amortized cost	139,516	126,509
Gross unrealized gains	2,808	1,458
Gross unrealized losses	1,783	2,985
Estimated fair value	140,541	124,982
Residential mortgage-backed securities
Available-for-sale securities:
Amortized cost	196,624	150,212
Gross unrealized gains	982	62
Gross unrealized losses	10,380	16,462
Estimated fair value	187,226	133,812
Other debt securities
Available-for-sale securities:
Amortized cost	34,863	27,232
Gross unrealized gains	543	147
Gross unrealized losses	254	628
Estimated fair value	35,152	26,751
U.S. Treasury
Available-for-sale securities:
Amortized cost	24,116
Gross unrealized gains	106
Gross unrealized losses	59
Estimated fair value	24,163
Total available-for-sale securities
Available-for-sale securities:
Amortized cost	1,363,228	1,065,956
Gross unrealized gains	17,425	6,806
Gross unrealized losses	15,825	29,147
Estimated fair value	1,364,828	1,043,615
Held-to-maturity securities:
Fair value of securities lent	44,400
Held-to-maturity securities
Held-to-maturity securities:
Amortized cost	4,833	4,833
Gross unrealized gains	30	101
Gross unrealized losses	0	0
Estimated fair value	$ 4,863	$ 4,934