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ADVANCES FROM THE FEDERAL HOME LOAN BANK (FHLB) - Narratives (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Federal Home Loan Bank Advances Branch Of F H L B Bank [Line Items]    
Minimum amount of qualifying mortgage collateral with a market value, percent 125.00%  
Loans Pledged As Collateral Fair Value $ 1,400.0 $ 1,400.0
Carrying value of mortgage loans 1,900.0 2,000.0
Additional capacity on credit facility based on collateral pledged at the FHLB 683.6  
Federal Home Loan Bank Advances [Member]    
Federal Home Loan Bank Advances Branch Of F H L B Bank [Line Items]    
Carrying value of mortgage loans $ 1,700.0 $ 1,700.0