Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 5,979,045	$ 5,926,785
Fair Value	5,564,053	5,409,698
Assets held by insurance regulatory requirements	12,100	11,800
Assets held in trust for the benefit of contractual counterparties	130,700	128,400
Total fixed income securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,979,045	5,926,785
Gross Unrealized Gains	11,585	5,953
Gross Unrealized Losses	(426,577)	(523,040)
Fair Value	5,564,053	5,409,698
U.S. Treasury securities and obligations of U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	223,428	145,581
Gross Unrealized Gains	31	2
Gross Unrealized Losses	(7,713)	(9,683)
Fair Value	215,746	135,900
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,403,603	2,400,261
Gross Unrealized Gains	9,776	4,866
Gross Unrealized Losses	(201,039)	(256,073)
Fair Value	2,212,340	2,149,054
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,341,134	2,416,475
Gross Unrealized Gains	1,733	1,043
Gross Unrealized Losses	(164,925)	(196,377)
Fair Value	2,177,942	2,221,141
ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	124,175	126,723
Gross Unrealized Gains	15	5
Gross Unrealized Losses	(4,819)	(6,041)
Fair Value	119,371	120,687
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	217,751	223,743
Gross Unrealized Gains	10	10
Gross Unrealized Losses	(22,256)	(25,744)
Fair Value	195,505	198,009
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	250,589	257,785
Gross Unrealized Gains	20	22
Gross Unrealized Losses	(18,704)	(20,591)
Fair Value	231,905	237,216
CLOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	337,033	337,656
Gross Unrealized Gains	0	5
Gross Unrealized Losses	(6,459)	(7,829)
Fair Value	330,574	329,832
Foreign government debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,486	4,486
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(659)	(699)
Fair Value	3,827	3,787
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	76,846	14,075
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3)	(3)
Fair Value	$ 76,843	$ 14,072

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

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