Investment in Loans (Schedule of Residential Mortgage Loans: Geographic Distribution) (Details) - Financing Receivables, Unpaid Principal Balance [Member] - Residential mortgage loans - Geographic Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	100.00%	100.00%
CALIFORNIA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	43.10%	46.60%
Florida [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	14.80%	11.90%
Texas [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	10.20%	11.90%
Colorado [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	3.10%	3.20%
MASSACHUSETTS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	2.60%	2.90%
MASSACHUSETTS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.40%	1.60%
NEVADA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.90%	1.60%
OREGON
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	2.20%	2.20%
ARIZONA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	2.00%	2.40%
UTAH
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.70%	1.90%
Maryland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.60%	1.30%
MARYLAND
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.00%	1.10%
NORTH CAROLINA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.10%	0.80%
NEW JERSEY
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.40%	1.10%
ILLINOIS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.80%	1.70%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	8.80%	7.10%
GEORGIA
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.30%	0.70%