Investment in Loans (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	$ 1,026,983
Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairments	100
Unpaid principal balance, impairments	2,200
Fair value, impairments	1,900
In process of foreclosure	8,100
Unpaid Principal Balance	577,880
Loans, at fair value	562,763
Residential mortgage loans | Non-performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	15,795
Loans, at fair value	13,678
Commercial mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Principal Balance	264,932
Loans, at fair value	$ 239,623
Commercial mortgage loans | Non-performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan	5
Unpaid Principal Balance	$ 65,200
Loans, at fair value	40,800
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairments	2,100
Unpaid principal balance, impairments	173,800
Fair value, impairments	181,300
Unpaid Principal Balance	184,171
Loans, at fair value	$ 192,115