Fair Value Measurements (Summarize Changes in Level 3 Assets) (Details) - USD ($)	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, impairments		$ 0
Securities transferred into or out of level 3, net	$ 0		$ 0
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	17,488,000	20,590,000	20,590,000
Assets, earnings	(306,000)	(6,871,000)
Assets, other comprehensive income	0	0
Impairment of Intangible Assets (Excluding Goodwill)	0
Assets, purchases	0	5,611,000
Assets, (sales)	0	(1,842,000)
Assets, maturities	0	0
Assets. transfers out		0
Securities transferred into or out of level 3, net	0
Assets, ending balance	17,182,000		17,488,000
Level 3 | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	13,898,000	20,590,000	20,590,000
Assets, earnings	(381,000)	(6,692,000)
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	925,000
Assets, (sales)	0	(925,000)
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	13,517,000		13,898,000
Level 3 | Common stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	2,599,000	9,294,000	9,294,000
Assets, earnings	(381,000)	(6,695,000)
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	0
Assets, (sales)	0	0
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	2,218,000		2,599,000
Level 3 | Preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	11,299,000	11,296,000	11,296,000
Assets, earnings	0	3,000
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	925,000
Assets, (sales)	0	(925,000)
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	11,299,000		11,299,000
Level 3 | Arbitrage trading account
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	3,590,000	0	0
Assets, earnings	75,000	(179,000)
Assets, other comprehensive income	0	0
Impairment of Intangible Assets (Excluding Goodwill)	0
Assets, impairments		0
Assets, purchases	0	4,686,000
Assets, (sales)	0	(917,000)
Assets, maturities	0	0
Assets. transfers out		$ 0
Securities transferred into or out of level 3, net	0
Assets, ending balance	$ 3,665,000		$ 3,590,000