| Marketable securities |
| | March 31, 2020 | |
|
| | Cost
Basis
| | | Gross Unrealized Gains
| | | Gross Unrealized Losses
| | | Fair Value | |
| Certificates of deposit | | $ | 10,485,000 | | | $ | 25,000 | | | $ | — | | | $ | 10,510,000 | |
| Fixed income mutual funds | | | 3,560,000 | | | | — | | | | (246,000 | ) | | | 3,314,000 | |
| Corporate bonds and notes | | | 4,689,000 | | | | — | | | | (104,000 | ) | | | 4,585,000 | |
| Total marketable securities | | $ | 18,734,000 | | | $ | 25,000 | | | $ | (350,000 | ) | | $ | 18,409,000 | |
| | December 31, 2019 | |
|
| | Cost
Basis
| | | Gross Unrealized Gains
| | | Gross Unrealized Losses
| | | Fair Value | |
| Certificates of deposit | | $ | 8,953,000 | | | $ | 6,000 | | | $ | — | | | $ | 8,959,000 | |
| Fixed income mutual funds | | | 7,878,000 | | | | 1,000 | | | $ | — | | | | 7,879,000 | |
| Corporate bonds and notes | | | 8,813,000 | | | | 112,000 | | | | (33,000 | ) | | | 8,892,000 | |
| Total marketable securities | | $ | 25,644,000 | | | $ | 119,000 | | | $ | (33,000 | ) | | $ | 25,730,000 | |
|