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Investments (Investments Held in a Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Fair value
Fair Value	$ 3,247,055	$ 2,088,498
Less than 12 Months, Fair Value	2,874,080	1,947,941
More than 12 Months, Fair Value	372,975	140,557
Unrealized Loss
Unrealized Loss	302,442	30,815
Less than 12 Months, Unrealized Loss	256,450	25,389
More than 12 Months, Unrealized Loss	45,992	5,426
U.S. Treasury obligations
Fair value
Fair Value	214,422	190,054
Less than 12 Months, Fair Value	198,517	181,689
More than 12 Months, Fair Value	15,905	8,365
Unrealized Loss
Unrealized Loss	16,692	2,424
Less than 12 Months, Unrealized Loss	15,632	2,206
More than 12 Months, Unrealized Loss	1,060	218
U.S. Government-sponsored enterprise obligations
Fair value
Fair Value	17,509	16,287
Less than 12 Months, Fair Value	13,571	16,287
More than 12 Months, Fair Value	3,938	0
Unrealized Loss
Unrealized Loss	1,195	262
Less than 12 Months, Unrealized Loss	732	262
More than 12 Months, Unrealized Loss	463	0
State and municipal bonds
Fair value
Fair Value	410,783	175,442
Less than 12 Months, Fair Value	385,075	171,930
More than 12 Months, Fair Value	25,708	3,512
Unrealized Loss
Unrealized Loss	32,105	2,174
Less than 12 Months, Unrealized Loss	29,482	2,039
More than 12 Months, Unrealized Loss	2,623	135
Corporate debt
Fair value
Fair Value	1,644,974	945,196
Less than 12 Months, Fair Value	1,430,094	866,731
More than 12 Months, Fair Value	214,880	78,465
Unrealized Loss
Unrealized Loss	171,752	14,949
Less than 12 Months, Unrealized Loss	143,101	11,828
More than 12 Months, Unrealized Loss	28,651	3,121
Residential mortgage-backed securities
Fair value
Fair Value	361,015	326,248
Less than 12 Months, Fair Value	296,993	290,019
More than 12 Months, Fair Value	64,022	36,229
Unrealized Loss
Unrealized Loss	42,737	5,751
Less than 12 Months, Unrealized Loss	33,182	4,320
More than 12 Months, Unrealized Loss	9,555	1,431
Agency commercial mortgage-backed securities
Fair value
Fair Value	11,940	4,529
Less than 12 Months, Fair Value	9,724	4,355
More than 12 Months, Fair Value	2,216	174
Unrealized Loss
Unrealized Loss	602	62
Less than 12 Months, Unrealized Loss	448	54
More than 12 Months, Unrealized Loss	154	8
Other commercial mortgage-backed securities
Fair value
Fair Value	202,104	151,827
Less than 12 Months, Fair Value	185,243	145,467
More than 12 Months, Fair Value	16,861	6,360
Unrealized Loss
Unrealized Loss	16,607	2,273
Less than 12 Months, Unrealized Loss	15,068	1,884
More than 12 Months, Unrealized Loss	1,539	389
Other asset-backed securities
Fair value
Fair Value	384,308	278,915
Less than 12 Months, Fair Value	354,863	271,463
More than 12 Months, Fair Value	29,445	7,452
Unrealized Loss
Unrealized Loss	20,752	2,920
Less than 12 Months, Unrealized Loss	18,805	2,796
More than 12 Months, Unrealized Loss	$ 1,947	$ 124

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