Investment in Loans (Schedule of Residential Mortgage Loans: Geographic Distribution) (Details) - Financing Receivables, Unpaid Principal Balance [Member] - Residential mortgage loans - Geographic Concentration Risk [Member]	6 Months Ended
	Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	100.00%
California [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	48.80%
Florida [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	12.90%
Texas [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	12.60%
Colorado [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	3.80%
Arizona [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	3.00%
Oregon [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	2.30%
New York [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.80%
Nevada [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.90%
Utah [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.80%
WASHINGTON
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.80%
Maryland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.20%
ILLINOIS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	1.00%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of Total Outstanding Unpaid Principal Balance	7.10%