Residential Whole Loans (Other Loans at Carrying Value) (Details) $ in Millions	Jun. 30, 2018 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of other loans at carrying value | loan	6
Unpaid balance of other loans	$ 2.1
Total outstanding principal balance of all of the Company’s Other Loans at Carrying Value	0.20%
Rehabilitation loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitment to lend, unfunded	$ 29.7