Investments - Cost and Fair Value, Net of Credit Loss Allowance, of Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Available-for-sale securities
Amortized cost	$ 947,605
Estimated fair value	889,727
Corporate debt securities
Available-for-sale securities
Amortized cost	586,857	$ 565,997
Gross unrealized gains	187	9,663
Gross unrealized losses	33,921	2,495
Estimated fair value	553,123	573,165
Collateralized debt obligations
Available-for-sale securities
Amortized cost	102,868	115,344
Gross unrealized gains	52	456
Gross unrealized losses	3,701	338
Estimated fair value	99,219	115,462
Commercial mortgage-backed securities
Available-for-sale securities
Amortized cost	74,778	88,636
Gross unrealized gains	49	1,465
Gross unrealized losses	5,978	777
Estimated fair value	68,849	89,324
Residential mortgage-backed securities
Available-for-sale securities
Amortized cost	150,035	140,217
Gross unrealized gains	56	1,007
Gross unrealized losses	13,088	1,302
Estimated fair value	137,003	139,922
Other debt securities
Available-for-sale securities
Amortized cost	21,771	23,859
Gross unrealized gains	17	197
Gross unrealized losses	1,406	136
Estimated fair value	20,382	23,920
U.S. Treasury
Available-for-sale securities
Amortized cost	11,296	4,226
Gross unrealized gains	5	73
Gross unrealized losses	150	7
Estimated fair value	11,151	4,292
Available-for-sale securities
Available-for-sale securities
Amortized cost	947,605	938,279
Gross unrealized gains	366	12,861
Gross unrealized losses	58,244	5,055
Estimated fair value	$ 889,727	$ 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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Amortized cost of 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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