Intangible Assets Intangible assets consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): | | | | | | | | | | | | | | | | March 31, 2018 | | | Gross Carrying
Value | | Accumulated
Amortization | | Net Carrying
Value | Customer relationships | | $ | 790 |
| | $ | (566 | ) | | $ | 224 |
| Technology | | 4,811 |
| | (4,072 | ) | | 739 |
| Trademarks | | 930 |
| | (570 | ) | | 360 |
| Partner relationships | | 680 |
| | (680 | ) | | — |
| Non-compete agreements | | 40 |
| | (40 | ) | | — |
| Domain names | | 273 |
| | (273 | ) | | — |
| Patents | | 285 |
| | (211 | ) | | 74 |
| | | $ | 7,809 |
| | $ | (6,412 | ) | | $ | 1,397 |
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| | | | | | | | | | | | | | | | December 31, 2017 | | | Gross Carrying
Value | | Accumulated
Amortization | | Net Carrying
Value | Customer relationships | | $ | 790 |
| | $ | (538 | ) | | $ | 252 |
| Technology | | 4,811 |
| | (3,871 | ) | | 940 |
| Trademarks | | 930 |
| | (539 | ) | | 391 |
| Partner relationships | | 680 |
| | (623 | ) | | 57 |
| Non-compete agreements | | 40 |
| | (37 | ) | | 3 |
| Domain names | | 273 |
| | (273 | ) | | — |
| Patents | | 285 |
| | (203 | ) | | 82 |
| | | $ | 7,809 |
| | $ | (6,084 | ) | | $ | 1,725 |
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Amortization expense for the three months ended March 31, 2018 and 2017 was $0.3 million for each period. As of March 31, 2018, estimated future amortization of intangible assets was as follows (in thousands): | | | | | | Years Ending December 31, | 2018 | | $ | 601 |
| 2019 | | 352 |
| 2020 | | 259 |
| 2021 | | 124 |
| 2022 | | 61 |
| Total amortization expense | | $ | 1,397 |
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