MARKETABLE SECURITIES - Amortized cost basis, fair value and net unrealized gains on available-for-sale securities (Details 2) - USD ($) $ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Amortized Cost Basis | $ 11,570 | $ 13,101 |
| Fair Value | 11,512 | 13,031 |
| Net Unrealized Losses | (58) | (70) |
| Municipal Obligations | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Amortized Cost Basis | 9,820 | 13,101 |
| Fair Value | 9,764 | 13,031 |
| Net Unrealized Losses | (56) | (70) |
| Corporate Obligations | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Amortized Cost Basis | 1,750 | 0 |
| Fair Value | 1,748 | 0 |
| Net Unrealized Losses | $ (2) | $ 0 |