Fair Value Measurements (Summarize Changes in Level 3 Assets) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, impairments	$ 0	$ 0
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	29,948,000	20,385,000
Assets, earnings	351,000	(456,000)
Assets, other comprehensive income	46,000	46,000
Assets, purchases	0	11,523,000
Assets, (sales)	(17,508,000)	(7,353,000)
Assets. transfers out	3,509,000	5,803,000
Assets, ending balance	16,346,000
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, beginning balance	793,000
Liabilities, earnings	60,000
Liabilities, other comprehensive income	0
Liabilities, impairments	0
Liabilities, purchases	2,087,000
Liabilities, (sales)	(2,940,000)
Liabilities, maturities	0
Liabilities, ending balance	0
Level 3 | Debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	99,000	172,000
Assets, earnings	2,000	(2,000)
Assets, other comprehensive income	46,000	46,000
Assets, impairments	0	0
Assets, purchases	0	0
Assets, (sales)	(122,000)	(117,000)
Assets. transfers out	0	0
Assets, ending balance	25,000
Level 3 | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	99,000	172,000
Assets, earnings	2,000	(2,000)
Assets, other comprehensive income	46,000	46,000
Assets, impairments	0	0
Assets, purchases	0	0
Assets, (sales)	(122,000)	(117,000)
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	25,000
Level 3 | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	12,541,000	20,213,000
Assets, earnings	191,000	(448,000)
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	0
Assets, (sales)	0	(7,225,000)
Assets, maturities		0
Assets. transfers out	1,000	1,000
Assets, ending balance	12,733,000
Level 3 | Common stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	8,596,000	9,370,000
Assets, earnings	191,000	(548,000)
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	0
Assets, (sales)	0	(227,000)
Assets. transfers out	1,000	1,000
Assets, ending balance	8,788,000
Level 3 | Preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	3,945,000	10,843,000
Assets, earnings	0	100,000
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0
Assets, (sales)	0	(6,998,000)
Assets. transfers out	0	0
Assets, ending balance	3,945,000
Level 3 | Arbitrage trading account
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	17,308,000	0
Assets, earnings	158,000	(6,000)
Assets, other comprehensive income	0	0
Assets, impairments	0	0
Assets, purchases	0	11,523,000
Assets, (sales)	(17,386,000)	(11,000)
Assets. transfers out	3,508,000	$ 5,802,000
Assets, ending balance	3,588,000
Level 3 | Securities Sold, Not yet Purchased [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Liabilities, transfers out	$ 0