INCOME TAXES - Statutory federal rate (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
INCOME TAXES                      
Expected income taxes                 $ 17,648 $ 12,424 $ 5,414
Less income tax effect of:                      
Tax exempt interest                 (1,670) (1,934) (1,809)
Interest expense disallowance                 33 29 38
State tax, net of federal benefit                 3,132 1,292 1,540
Increase in cash surrender value of life insurance policies                 (1,007) (516) (373)
Indemnification income                   (311)  
Valuation allowance                 631    
Other                 122 107 (159)
Actual income tax expense $ 8,327 $ 4,102 $ 3,683 $ 2,777 $ 2,811 $ 1,928 $ 2,762 $ 3,590 $ 18,889 $ 11,091 $ 4,651