SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - CONCENTRATION (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Mortgage Banking Activities      
Initial amortization period of MSRs 7 years    
Impairment in MSR portfolio $ 0 $ 0  
Loan servicing income $ 1,983 $ 1,896 $ 1,752
Geographic concentration risk | California      
Concentration of credit risk      
Percentage of concentration risk 75.00%    
Warehouse lines of credit | Geographic concentration risk | California      
Concentration of credit risk      
Percentage of concentration risk 25.00%    
Net income | Geographic concentration risk | RPG | TRS division      
Concentration of credit risk      
Percentage of concentration risk 20.00% 13.00% 12.00%
Net income | Geographic concentration risk | Warehouse Lending      
Concentration of credit risk      
Percentage of concentration risk 8.00% 7.00% 5.00%