RESIDENTIAL MORTGAGE LOANS - Fair Value and Unpaid Principal of Residential Mortgage Loan Portfolio (Details) - Residential Mortgage - USD ($) $ in Thousands |
Jun. 30, 2018 |
Dec. 31, 2017 |
---|---|---|
Mortgage Loans on Real Estate [Line Items] | ||
Fair value | $ 1,666,157 | $ 1,438,322 |
Unpaid principal balance | $ 1,658,358 | $ 1,419,807 |