Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 6,056,298	$ 5,926,785
Fair Value	5,603,038	5,409,698
Short term fixed income securities investments held by company	172,800	67,000
Assets held by insurance regulatory requirements	11,900	11,800
Assets held in trust for the benefit of contractual counterparties	146,300	128,400
Total fixed income securities (1)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,056,298	5,926,785
Gross Unrealized Gains	5,103	5,953
Gross Unrealized Losses	(458,363)	(523,040)
Fair Value	5,603,038	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	185,239	145,581
Gross Unrealized Gains	8	2
Gross Unrealized Losses	(8,871)	(9,683)
Fair Value	176,376	135,900
Obligations of U.S. states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,208,970	2,400,261
Gross Unrealized Gains	3,996	4,866
Gross Unrealized Losses	(214,788)	(256,073)
Fair Value	1,998,178	2,149,054
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,542,461	2,416,475
Gross Unrealized Gains	1,040	1,043
Gross Unrealized Losses	(178,099)	(196,377)
Fair Value	2,365,402	2,221,141
ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	127,142	126,723
Gross Unrealized Gains	3	5
Gross Unrealized Losses	(5,191)	(6,041)
Fair Value	121,954	120,687
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	260,147	223,743
Gross Unrealized Gains	7	10
Gross Unrealized Losses	(23,583)	(25,744)
Fair Value	236,571	198,009
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	301,682	257,785
Gross Unrealized Gains	42	22
Gross Unrealized Losses	(22,152)	(20,591)
Fair Value	279,572	237,216
CLOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	335,380	337,656
Gross Unrealized Gains	6	5
Gross Unrealized Losses	(4,935)	(7,829)
Fair Value	330,451	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	(743)	(699)
Fair Value	3,743	3,787
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	90,791	14,075
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(1)	(3)
Fair Value	$ 90,791	$ 14,072

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

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