Investments (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) item security	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) item security	Jun. 30, 2022 USD ($)	Dec. 31, 2022 security
Schedule of Available-for-sale Securities [Line Items]
Number of investment in unaffiliated issuers | item	82		82
Investment in common stock (as percentage)	86.00%		86.00%
Investment in debt securities (as percentage)	94.00%		94.00%
Gross gains on investments	$ 800,000	$ 1,000,000.0	$ 1,700,000	$ 1,200,000
Gross losses on investments	900,000	24,000	2,400,000	31,000
Proceeds from sale of investment securities	8,100,000	$ 4,000,000.0	58,500,000	$ 4,500,000
Debt securities, available-for-sale, allowance for expected credit losses	$ 0		$ 0
Debt Securities [Member]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Number of debt securities with unrealized loss | security	208		208		228
Number of debt securities with unrealized loss, less than 12 months | security	82		82		181
Number of debt securities with unrealized loss, greater than 12 months | security	126		126		47