Investments in Securities and Fair Value Investments in Securities (Schedule of Cost-method Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair​Value​Assets​Measured​On​Nonrecurring​Basis​Reconciliation​Calculation​Roll​Forward [Line Items]
Beginning balance	$ 8,741	$ 7,899
Other than Temporary Impairment Losses, Investments	0	0
Observable Changes	0	0
Purchases and Additional Commitments Paid	6,543	1,227
Sales, Returns of Capital, and Other Reductions	(1,609)	(385)
Ending balance	13,675	8,741
Real Estate Investment
Fair​Value​Assets​Measured​On​Nonrecurring​Basis​Reconciliation​Calculation​Roll​Forward [Line Items]
Beginning balance	0	0
Other than Temporary Impairment Losses, Investments	0	0
Observable Changes	0	0
Purchases and Additional Commitments Paid	5,000	0
Sales, Returns of Capital, and Other Reductions	(13)	0
Ending balance	4,987	0
Cost-method Investments
Fair​Value​Assets​Measured​On​Nonrecurring​Basis​Reconciliation​Calculation​Roll​Forward [Line Items]
Beginning balance	8,741	7,899
Other than Temporary Impairment Losses, Investments	0	0
Observable Changes	0	0
Purchases and Additional Commitments Paid	1,543	1,227
Sales, Returns of Capital, and Other Reductions	(1,596)	(385)
Ending balance	$ 8,688	$ 8,741