| INVESTMENT SECURITIES (Tables)
 | 9 Months Ended | 
| Sep. 30, 2019 | 
|---|
| Investments, Debt and Equity Securities [Abstract] |  | 
| Schedule of amortized cost and related market value of investment securities available-for-sale | 
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | Investment Portfolio Composition. The amortized cost and related market value of investment securities available-for-sale and |  | held-to-maturity were as follows: |  
|  | September 30, 2019 |  |  | December 31, 2018 |  
|  | Amortized | Unrealized | Unrealized | Market | Amortized | Unrealized | Unrealized | Market |  
|  | Cost |  | Gains |  | Losses |  | Value |  | Cost |  | Gain |  | Losses |  | Value |  
| Available for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Government Treasury | $ | 216,707 |  | $ | 858 |  | $ | 300 |  | $ | 217,265 |  | $ | 264,298 |  | $ | 167 |  | $ | 2,616 |  | $ | 261,849 |  
| U.S. Government Agency |  | 137,798 |  |  | 572 |  |  | 332 |  |  | 138,038 |  |  | 133,201 |  |  | 520 |  |  | 515 |  |  | 133,206 |  
| States and Political Subdivisions |  | 13,041 |  |  | 6 |  |  | 3 |  |  | 13,044 |  |  | 42,509 |  |  | - |  |  | 144 |  |  | 42,365 |  
| Mortgage-Backed Securities |  | 708 |  |  | 79 |  |  | - |  |  | 787 |  |  | 903 |  |  | 40 |  |  | - |  |  | 943 |  
| Equity Securities(1) |  | 7,847 |  |  | - |  |  | - |  |  | 7,847 |  |  | 7,794 |  |  | - |  |  | - |  |  | 7,794 |  
| Total | $ | 376,101 |  | $ | 1,515 |  | $ | 635 |  | $ | 376,981 |  | $ | 448,705 |  | $ | 727 |  | $ | 3,275 |  | $ | 446,157 |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Held to Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Government Treasury | $ | 25,050 |  | $ | 10 |  | $ | 46 |  | $ | 25,014 |  | $ | 35,088 |  | $ | - |  | $ | 477 |  | $ | 34,611 |  
| States and Political Subdivisions |  | 3,356 |  |  | - |  |  | 1 |  |  | 3,355 |  |  | 6,512 |  |  | - |  |  | 26 |  |  | 6,486 |  
| Mortgage-Backed Securities |  | 211,897 |  |  | 1,856 |  |  | 235 |  |  | 213,518 |  |  | 175,720 |  |  | 220 |  |  | 2,624 |  |  | 173,316 |  
| Total | $ | 240,303 |  | $ | 1,866 |  | $ | 282 |  | $ | 241,887 |  | $ | 217,320 |  | $ | 220 |  | $ | 3,127 |  | $ | 214,413 |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Total Investment Securities | $ | 616,404 |  | $ | 3,381 |  | $ | 917 |  | $ | 618,868 |  | $ | 666,025 |  | $ | 947 |  | $ | 6,402 |  | $ | 660,570 |  | 
| Schedule of investment securities with maturity distribution based on contractual maturities | 
|  | Available for Sale |  | Held to Maturity |  
| (Dollars in Thousands) | Amortized Cost |  | Market Value |  | Amortized Cost |  | Market Value |  
| Due in one year or less | $ | 141,609 |  | $ | 141,370 |  | $ | 13,354 |  | $ | 13,331 |  
| Due after one year through five years |  | 90,139 |  |  | 90,937 |  |  | 15,052 |  |  | 15,038 |  
| Mortgage-Backed Securities |  | 708 |  |  | 787 |  |  | 211,897 |  |  | 213,518 |  
| U.S. Government Agency |  | 135,798 |  |  | 136,040 |  |  | - |  |  | - |  
| Equity Securities |  | 7,847 |  |  | 7,847 |  |  | - |  |  | - |  
| Total | $ | 376,101 |  | $ | 376,981 |  | $ | 240,303 |  | $ | 241,887 |  | 
| Schedule of investment securities with continuous unrealized loss position | 
|  | Less Than |  | Greater Than |  |  |  |  |  |  |  
|  | 12 Months |  | 12 Months |  | Total |  
|  | Market |  | Unrealized |  | Market |  | Unrealized |  | Market |  | Unrealized |  
| (Dollars in Thousands) | Value |  | Losses |  | Value |  | Losses |  | Value |  | Losses |  
| September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Available for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Government Treasury | $ | 4,973 |  | $ | 8 |  | $ | 128,152 |  | $ | 292 |  | $ | 133,125 |  | $ | 300 |  
| U.S. Government Agency |  | 29,698 |  |  | 179 |  |  | 28,524 |  |  | 153 |  |  | 58,222 |  |  | 332 |  
| States and Political Subdivisions |  | 5,428 |  |  | 3 |  |  | - |  |  | - |  |  | 5,428 |  |  | 3 |  
| Total |  | 40,099 |  |  | 190 |  |  | 156,676 |  |  | 445 |  |  | 196,775 |  |  | 635 |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Held to Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Government Treasury |  | - |  |  | - |  |  | 19,996 |  |  | 46 |  |  | 19,996 |  |  | 46 |  
| States and Political Subdivisions |  | 1,794 |  |  | 1 |  |  | 500 |  |  | - |  |  | 2,294 |  |  | 1 |  
| Mortgage-Backed Securities |  | 29,466 |  |  | 78 |  |  | 16,318 |  |  | 157 |  |  | 45,784 |  |  | 235 |  
| Total | $ | 31,260 |  | $ | 79 |  | $ | 36,814 |  | $ | 203 |  | $ | 68,074 |  | $ | 282 |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| December 31, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Available for Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Government Treasury | $ | 28,420 |  | $ | 80 |  | $ | 193,501 |  | $ | 2,536 |  | $ | 221,921 |  | $ | 2,616 |  
| U.S. Government Agency |  | 53,237 |  |  | 271 |  |  | 28,735 |  |  | 244 |  |  | 81,972 |  |  | 515 |  
| States and Political Subdivisions |  | 8,243 |  |  | 12 |  |  | 31,417 |  |  | 132 |  |  | 39,660 |  |  | 144 |  
| Mortgage-Backed Securities |  | 10 |  |  | - |  |  | - |  |  | - |  |  | 10 |  |  | - |  
| Total |  | 89,910 |  |  | 363 |  |  | 253,653 |  |  | 2,912 |  |  | 343,563 |  |  | 3,275 |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Held to Maturity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| U.S. Government Treasury |  | - |  |  | - |  |  | 34,612 |  |  | 477 |  |  | 34,612 |  |  | 477 |  
| States and Political Subdivisions |  | 204 |  |  | - |  |  | 6,281 |  |  | 26 |  |  | 6,485 |  |  | 26 |  
| Mortgage-Backed Securities |  | 51,327 |  |  | 389 |  |  | 84,705 |  |  | 2,235 |  |  | 136,032 |  |  | 2,624 |  
| Total | $ | 51,531 |  | $ | 389 |  | $ | 125,598 |  | $ | 2,738 |  | $ | 177,129 |  | $ | 3,127 |  |