Investments in Securities and Fair Value Investments in Securities (Schedule of Gross Realized Gains and Losses on Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total, gross realized gains	$ 3,458	$ 1,725
Total, gross realized losses	(3,147)	(382)
Net realized gains from securities	311	1,343
Gains on other investments	31	3
Losses on investments	(9)	(6)
Other investments, realized investment gains (losses)	22	(3)
Net realized investment gains	333	1,340
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Total, gross realized gains	30	0
Common stocks and nonredeemable preferred stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities, realized gain (loss)	3,428	1,725
Total, gross realized losses	(2,665)	(382)
Other than temporary impairment of securities
Debt Securities, Available-for-sale [Line Items]
Total, gross realized losses	$ (482)	$ 0