Investments - Debt Securities Available-for-sale, Unrealized Loss Position, Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Line Items]
Basis		$ 417,263
Gross unrealized losses		(25,649)
Fair value		391,614
Debt securities due February 2028
Investments, Debt and Equity Securities [Line Items]
Basis	$ 37,206	38,843
Gross unrealized losses	(422)	(82)
Fair value	36,784	38,761
Debt securities due November 2051
Investments, Debt and Equity Securities [Line Items]
Basis	3,763	36,829
Gross unrealized losses	(122)	(2,429)
Fair value	3,641	34,400
Debt securities due September 2059
Investments, Debt and Equity Securities [Line Items]
Basis		14,945
Gross unrealized losses		(1,045)
Fair value		13,900
Debt securities due September 2059 One
Investments, Debt and Equity Securities [Line Items]
Gross unrealized losses		(600)
Debt securities due September 2059 Two
Investments, Debt and Equity Securities [Line Items]
Basis	2,075
Gross unrealized losses	(77)	(500)
Fair value	1,998
Debt securities due November 2059
Investments, Debt and Equity Securities [Line Items]
Basis		6,752
Gross unrealized losses		(313)
Fair value		6,439
Debt securities due December 2059
Investments, Debt and Equity Securities [Line Items]
Basis	23,534	33,569
Gross unrealized losses	(960)	(2,083)
Fair value	22,574	31,486
Debt securities due March 2060
Investments, Debt and Equity Securities [Line Items]
Basis	6,062	14,492
Gross unrealized losses	(769)	(1,909)
Fair value	5,293	12,583
Debt securities due June 2060
Investments, Debt and Equity Securities [Line Items]
Basis	3,757	8,002
Gross unrealized losses	(124)	(394)
Fair value	3,633	7,608
Debt securities due September 2060
Investments, Debt and Equity Securities [Line Items]
Basis	1,464	3,242
Gross unrealized losses	(30)	(15)
Fair value	1,434	3,227
Debt securities due December 2060
Investments, Debt and Equity Securities [Line Items]
Basis	21,906	43,216
Gross unrealized losses	(4,451)	(7,868)
Fair value	17,455	35,348
Debt securities due January 2061
Investments, Debt and Equity Securities [Line Items]
Basis	4,886	11,883
Gross unrealized losses	(619)	(1,342)
Fair value	4,267	10,541
Debt securities due June 2061
Investments, Debt and Equity Securities [Line Items]
Basis	13,367	47,302
Gross unrealized losses	(1,618)	(6,303)
Fair value	11,749	40,999
Debt Securities due June 2061, Security One
Investments, Debt and Equity Securities [Line Items]
Gross unrealized losses	(500)	(3,000)
Debt Securities due June 2061, Security Two
Investments, Debt and Equity Securities [Line Items]
Gross unrealized losses	(1,100)	(3,300)
Debt securities due October 2061
Investments, Debt and Equity Securities [Line Items]
Basis	12,061	12,401
Gross unrealized losses	(1,177)	(1,013)
Fair value	10,884	11,388
Debt securities due March 2062
Investments, Debt and Equity Securities [Line Items]
Basis	10,687	11,096
Gross unrealized losses	(1,049)	(853)
Fair value	9,638	10,243
Debt Securities Due July 2062
Investments, Debt and Equity Securities [Line Items]
Basis	12,961
Gross unrealized losses	(342)
Fair value	12,619
Total basis
Investments, Debt and Equity Securities [Line Items]
Basis	153,729	282,572
Total gross unrealized losses
Investments, Debt and Equity Securities [Line Items]
Gross unrealized losses	(11,760)	(25,649)
Total carrying value (fair value)
Investments, Debt and Equity Securities [Line Items]
Fair value	$ 141,969	$ 256,923