Investments - Cost and Fair Value, Net of Credit Loss Allowance, of Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available-for-sale securities
Amortized cost	$ 961,135
Estimated fair value	894,661
Corporate debt securities
Available-for-sale securities
Amortized cost	588,536	$ 565,997
Gross unrealized gains	657	9,663
Gross unrealized losses	35,811	2,495
Estimated fair value	553,382	573,165
Collateralized debt obligations
Available-for-sale securities
Amortized cost	107,730	115,344
Gross unrealized gains	11	456
Gross unrealized losses	5,204	338
Estimated fair value	102,537	115,462
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	73,855	88,636
Gross unrealized gains	157	1,465
Gross unrealized losses	7,958	777
Estimated fair value	66,054	89,324
Residential mortgage-backed securities
Available-for-sale securities
Amortized cost	166,412	140,217
Gross unrealized gains	72	1,007
Gross unrealized losses	16,069	1,302
Estimated fair value	150,415	139,922
Other debt securities
Available-for-sale securities
Amortized cost	24,602	23,859
Gross unrealized gains	0	197
Gross unrealized losses	2,329	136
Estimated fair value	22,273	23,920
U.S. Treasury
Available-for-sale securities
Amortized cost		4,226
Gross unrealized gains		73
Gross unrealized losses		7
Estimated fair value		4,292
Available-for-sale securities
Available-for-sale securities
Amortized cost	961,135	938,279
Gross unrealized gains	897	12,861
Gross unrealized losses	67,371	5,055
Estimated fair value	$ 894,661	$ 946,085

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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