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, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Total, gross realized gains	$ 1,725	$ 1,030	$ 1,487
Total, gross realized losses	(382)	(1,147)	(286)
Net realized gains (losses) from securities	1,343	(117)	1,201
Impairments on other investments	0	0	(182)
Gains on other investments	3	7	22
Losses on investments	(6)	0	0
Other investments, realized investment gains (losses)	(3)	7	(160)
Net realized investment gains (losses)	1,340	(110)	1,041
Common stocks and nonredeemable preferred stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities, realized gain (loss)	1,725	1,030	1,487
Total, gross realized losses	(382)	(1,147)	(260)
Other than temporary impairment of securities
Debt Securities, Available-for-sale [Line Items]
Total, gross realized losses	$ 0	$ 0	$ (26)