Debt Securities - Debt securities in an unrealized loss position (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair Value
Less than 12 months	$ 1,393,540	$ 2,676,734
12 months or more	1,139,006	106,443
Total	2,532,546	2,783,177
Unrealized Losses
Less than 12 months	(133,067)	(49,847)
Unrealized Losses	(195,800)	(4,807)
Total	(328,867)	(54,654)
Fair Value
Less than 12 months	271,660
12 months or more	537,225
Total	808,885	0
Unrealized Losses
Less than 12 months	(44,835)
12 months or more	(82,608)
Total	(127,443)	0
U.S. Treasury securities
Fair Value
Less than 12 months	2,067	163,653
12 months or more	138,775	0
Total	140,842	163,653
Unrealized Losses
Less than 12 months	(5)	(1,047)
Unrealized Losses	(4,648)	0
Total	(4,653)	(1,047)
Obligations of U.S. government corporations and agencies
Fair Value
Less than 12 months	21,629
12 months or more	0
Total	21,629
Unrealized Losses
Less than 12 months	(358)
Unrealized Losses	0
Total	(358)
Obligations of states and political subdivisions
Fair Value
Less than 12 months	220,960	92,680
12 months or more	41,779	0
Total	262,739	92,680
Unrealized Losses
Less than 12 months	(20,029)	(1,493)
Unrealized Losses	(7,824)	0
Total	(27,853)	(1,493)
Asset-backed securities
Fair Value
Less than 12 months	441,896	89,983
12 months or more	24,628	0
Total	466,524	89,983
Unrealized Losses
Less than 12 months	(21,681)	(164)
Unrealized Losses	(1,871)	0
Total	(23,552)	(164)
Commercial mortgage-backed securities
Fair Value
Less than 12 months	74,334	389,078
12 months or more	13,417	85,905
Total	87,751	474,983
Unrealized Losses
Less than 12 months	(8,761)	(10,186)
Unrealized Losses	(2,207)	(3,580)
Total	(10,968)	(13,766)
Fair Value
Less than 12 months	109,085
12 months or more	316,690
Total	425,775
Unrealized Losses
Less than 12 months	(15,592)
12 months or more	(44,749)
Total	(60,341)
Residential mortgage-backed securities
Fair Value
Less than 12 months	557,046	1,700,187
12 months or more	747,141	20,538
Total	1,304,187	1,720,725
Unrealized Losses
Less than 12 months	(72,807)	(33,453)
Unrealized Losses	(161,188)	(1,227)
Total	(233,995)	(34,680)
Fair Value
Less than 12 months	162,575
12 months or more	220,535
Total	383,110
Unrealized Losses
Less than 12 months	(29,243)
12 months or more	(37,859)
Total	(67,102)
Corporate debt securities
Fair Value
Less than 12 months	75,608	241,153
12 months or more	173,266	0
Total	248,874	241,153
Unrealized Losses
Less than 12 months	(9,426)	(3,504)
Unrealized Losses	(18,062)	0
Total	$ (27,488)	$ (3,504)