| Fair value of marketable securities, by type |
The following table summarizes the fair value of these marketable securities, by level within the fair value hierarchy, as of each period end: | | | | | | | | | | | | | | | | | | | | | | | | | | June 30, 2013 | | December 31, 2012 | | Level 1 | | Level 2 | | Total | | Level 1 | | Level 2 | | Total | U.S. Treasury notes and bonds | $ | 2,844,625 |
| | $ | — |
| | $ | 2,844,625 |
| | $ | 2,473,596 |
| | $ | — |
| | $ | 2,473,596 |
| U.S. Agency issued mortgage-backed securities – variable rate | — |
| | 3,404,482 |
| | 3,404,482 |
| | — |
| | 3,708,920 |
| | 3,708,920 |
| U.S. Agency notes and bonds – fixed rate | — |
| | 1,495,905 |
| | 1,495,905 |
| | — |
| | 1,505,177 |
| | 1,505,177 |
| SBA loan pools – variable rate | — |
| | 1,893,627 |
| | 1,893,627 |
| | — |
| | 1,988,443 |
| | 1,988,443 |
| Municipal bonds – VRDN | 9,875,000 |
| | — |
| | 9,875,000 |
| | 7,010,000 |
| | — |
| | 7,010,000 |
| Total fair value of marketable securities | $ | 12,719,625 |
| | $ | 6,794,014 |
| | $ | 19,513,639 |
| | $ | 9,483,596 |
| | $ | 7,202,540 |
| | $ | 16,686,136 |
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