Investments - Available-for-sale Securities in a Gross Unrealized Loss Position by Length of Time (Details) $ in Thousands	Dec. 31, 2024 USD ($) holding	Dec. 31, 2023 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 280,332	$ 87,774
12 months or longer	260,480	517,090
Total	540,812	604,864
Unrealized losses
Less than 12 months	3,701	807
12 months or longer	22,664	32,511
Total	$ 26,365	$ 33,318
No. of holdings | holding	616	651
Non-investment grade
Fair value
Less than 12 months	$ 28,972	$ 8,493
12 months or longer	27,561	47,618
Total	56,533	56,111
Unrealized losses
Less than 12 months	702	270
12 months or longer	2,080	4,089
Total	$ 2,782	$ 4,359
No. of holdings | holding	370	385
Corporate debt securities
Fair value
Less than 12 months	$ 197,619	$ 50,853
12 months or longer	156,059	338,322
Total	353,678	389,175
Unrealized losses
Less than 12 months	2,486	546
12 months or longer	6,199	15,999
Total	$ 8,685	$ 16,545
No. of holdings | holding	567	590
Collateralized debt obligations
Fair value
Less than 12 months	$ 33,686	$ 3,911
12 months or longer	11,762	87,005
Total	45,448	90,916
Unrealized losses
Less than 12 months	71	15
12 months or longer	316	2,073
Total	$ 387	$ 2,088
No. of holdings | holding	77	142
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 28,333	$ 9,148
12 months or longer	24,966	30,145
Total	53,299	39,293
Unrealized losses
Less than 12 months	407	157
12 months or longer	2,578	4,552
Total	$ 2,985	$ 4,709
No. of holdings | holding	131	108
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 38,003	$ 30,271
12 months or longer	90,209	101,761
Total	128,212	132,032
Unrealized losses
Less than 12 months	1,289	297
12 months or longer	15,173	13,350
Total	$ 16,462	$ 13,647
No. of holdings | holding	169	164
Other debt securities
Fair value
Less than 12 months	$ 11,663	$ 2,084
12 months or longer	5,045	7,475
Total	16,708	9,559
Unrealized losses
Less than 12 months	150	62
12 months or longer	478	626
Total	$ 628	$ 688
No. of holdings | holding	42	32
Available-for-sale securities
Fair value
Less than 12 months	$ 309,304	$ 96,267
12 months or longer	288,041	564,708
Total	597,345	660,975
Unrealized losses
Less than 12 months	4,403	1,077
12 months or longer	24,744	36,600
Total	$ 29,147	$ 37,677
No. of holdings | holding	986	1,036