Investments - Available-For-Sale Securities in a Gross Unrealized Loss Position by Length of Time (Details) $ in Thousands	Sep. 30, 2025 USD ($) holding	Dec. 31, 2024 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 53,947	$ 280,332
12 months or longer	204,399	260,480
Total	258,346	540,812
Unrealized losses
Less than 12 months	408	3,701
12 months or longer	14,379	22,664
Total	$ 14,787	$ 26,365
No. of holdings | holding	344	616
Non-investment grade
Fair value
Less than 12 months	$ 20,173	$ 28,972
12 months or longer	20,121	27,561
Total	40,294	56,533
Unrealized losses
Less than 12 months	815	702
12 months or longer	1,079	2,080
Total	$ 1,894	$ 2,782
No. of holdings | holding	303	370
Corporate debt securities
Fair value
Less than 12 months	$ 23,443	$ 197,619
12 months or longer	107,364	156,059
Total	130,807	353,678
Unrealized losses
Less than 12 months	817	2,486
12 months or longer	2,413	6,199
Total	$ 3,230	$ 8,685
No. of holdings | holding	358	567
Collateralized debt obligations
Fair value
Less than 12 months	$ 25,562	$ 33,686
12 months or longer	5,396	11,762
Total	30,958	45,448
Unrealized losses
Less than 12 months	69	71
12 months or longer	99	316
Total	$ 168	$ 387
No. of holdings | holding	54	77
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 4,833	$ 28,333
12 months or longer	19,434	24,966
Total	24,267	53,299
Unrealized losses
Less than 12 months	55	407
12 months or longer	1,655	2,578
Total	$ 1,710	$ 2,985
No. of holdings | holding	66	131
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 17,132	$ 38,003
12 months or longer	88,556	90,209
Total	105,688	128,212
Unrealized losses
Less than 12 months	248	1,289
12 months or longer	11,052	15,173
Total	$ 11,300	$ 16,462
No. of holdings | holding	144	169
Other debt securities
Fair value
Less than 12 months	$ 1,681	$ 11,663
12 months or longer	3,770	5,045
Total	5,451	16,708
Unrealized losses
Less than 12 months	25	150
12 months or longer	239	478
Total	$ 264	$ 628
No. of holdings | holding	24	42
U.S. Treasury
Fair value
Less than 12 months	$ 1,469
12 months or longer	0
Total	1,469
Unrealized losses
Less than 12 months	9
12 months or longer	0
Total	$ 9
No. of holdings | holding	1
Available-for-sale securities
Fair value
Less than 12 months	$ 74,120	$ 309,304
12 months or longer	224,520	288,041
Total	298,640	597,345
Unrealized losses
Less than 12 months	1,223	4,403
12 months or longer	15,458	24,744
Total	$ 16,681	$ 29,147
No. of holdings | holding	647	986