Variable Interest Entities and Collateralized Loan Obligations - Summary of Variable Interest Entities Assets and Liabilities (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
ASSETS
Total Assets	$ 1,689,353	$ 1,926,612
LIABILITIES
Total Liabilities	(1,286,771)	(1,518,095)
Cash and Cash Equivalents
ASSETS
Total Assets	1,032	3,896
Accounts Receivable from Servicer/Trustee
ASSETS
Total Assets	6,562	94,763
Accrued Interest Receivable
ASSETS
Total Assets	3,130	3,672
Loans Held for Investment
ASSETS
Total Assets	1,678,629	1,824,281
Accrued Interest Payable
LIABILITIES
Total Liabilities	(2,632)	(2,637)
Accrued Expenses
LIABILITIES
Total Liabilities	(619)	(668)
Collateralized Loan Obligation
LIABILITIES
Total Liabilities	$ (1,283,520)	$ (1,514,790)