Investments - Available-For-Sale Securities in a Gross Unrealized Loss Position by Length of Time (Details) $ in Thousands	Sep. 30, 2024 USD ($) holding	Dec. 31, 2023 USD ($) holding
Investment grade
Fair value
Less than 12 months	$ 100,964	$ 87,774
12 months or longer	288,847	517,090
Total	389,811	604,864
Unrealized losses
Less than 12 months	248	807
12 months or longer	18,369	32,511
Total	$ 18,617	$ 33,318
No. of holdings | holding	486	651
Non-investment grade
Fair value
Less than 12 months	$ 21,657	$ 8,493
12 months or longer	30,557	47,618
Total	52,214	56,111
Unrealized losses
Less than 12 months	330	270
12 months or longer	2,163	4,089
Total	$ 2,493	$ 4,359
No. of holdings | holding	378	385
Corporate debt securities
Fair value
Less than 12 months	$ 56,346	$ 50,853
12 months or longer	170,974	338,322
Total	227,320	389,175
Unrealized losses
Less than 12 months	377	546
12 months or longer	6,128	15,999
Total	$ 6,505	$ 16,545
No. of holdings | holding	496	590
Collateralized debt obligations
Fair value
Less than 12 months	$ 39,689	$ 3,911
12 months or longer	19,694	87,005
Total	59,383	90,916
Unrealized losses
Less than 12 months	57	15
12 months or longer	559	2,073
Total	$ 616	$ 2,088
No. of holdings | holding	102	142
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 6,367	$ 9,148
12 months or longer	25,992	30,145
Total	32,359	39,293
Unrealized losses
Less than 12 months	48	157
12 months or longer	2,522	4,552
Total	$ 2,570	$ 4,709
No. of holdings | holding	85	108
Residential mortgage- backed securities
Fair value
Less than 12 months	$ 18,780	$ 30,271
12 months or longer	97,271	101,761
Total	116,051	132,032
Unrealized losses
Less than 12 months	82	297
12 months or longer	10,899	13,350
Total	$ 10,981	$ 13,647
No. of holdings | holding	152	164
Other debt securities
Fair value
Less than 12 months	$ 1,439	$ 2,084
12 months or longer	5,473	7,475
Total	6,912	9,559
Unrealized losses
Less than 12 months	14	62
12 months or longer	424	626
Total	$ 438	$ 688
No. of holdings | holding	29	32
Available-for-sale securities
Fair value
Less than 12 months	$ 122,621	$ 96,267
12 months or longer	319,404	564,708
Total	442,025	660,975
Unrealized losses
Less than 12 months	578	1,077
12 months or longer	20,532	36,600
Total	$ 21,110	$ 37,677
No. of holdings | holding	864	1,036