Other Assets and Liabilities - Additional Information (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) loan property	Dec. 31, 2015 USD ($)
Other Assets and Other Liabilities [Line Items]
Real estate owned (REO)		$ 3,354	$ 5,533
Amount related to transfers into REO		4,000
REO liquidations		10,000
Unrealized gain on REO from market value adjustments		3,000
Costs incurred and expensed	$ 10,000	$ 0	10,401	$ 0
Termination Benefits
Other Assets and Other Liabilities [Line Items]
Costs incurred and expensed			9,000
Contract Termination Costs
Other Assets and Other Liabilities [Line Items]
Costs incurred and expensed			$ 2,000
Commercial loans, at lower of cost or fair value
Other Assets and Other Liabilities [Line Items]
Number of Loans | loan			1
Total Principal			$ 3,000
Carrying value			3,000
Commercial loans, at lower of cost or fair value | Carrying Value
Other Assets and Other Liabilities [Line Items]
Carrying value			$ 3,000
Legacy Sequoia
Other Assets and Other Liabilities [Line Items]
Number of REO properties recorded on balance sheet | property		14	23