During the years ended December 31, 2015, 2014, and 2013, $13.3 million, $11.0 million and $10.7 million, respectively, of deferred revenue related to tenant-funded tenant improvements (including discontinued operations for the years ended December 31, 2014 and 2013) was amortized and recognized as rental income. The following is the estimated amortization of deferred revenue related to tenant-funded tenant improvements as of December 31, 2015 for the next five years and thereafter:
| | | | | Year Ending | (in thousands) | 2016 | $ | 12,536 |
| 2017 | 11,924 |
| 2018 | 11,285 |
| 2019 | 9,761 |
| 2020 | 9,230 |
| Thereafter | 36,089 |
| Total | $ | 90,825 |
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