pre_text: (6) Intangible Assets Intangible assets consist of the following (in thousands): During 2019, we periodically assessed whether any indicators of impairment existed related to our intangible assets. As of each interim period end during the year, we concluded that a triggering event had not occurred that would more likely than not reduce the fair value of our intangible assets below their carrying values. Amortization expense recognized in 2019, 2018 and 2017 was $23,671,000, $15,737,000 and $16,812,000, respectively.
table: December 31,
table: 2019 2018
table: Customer relationships $336,455 $159,566
table: Other 15,621 5,555
table: 352,076 165,121
table: Accumulated amortization (73,492) (52,942)
table: Intangible assets, net 278,584 112,179
question: Analyse this data from a financial earnings document. What is the change in Accumulated amortization between 2018 and 2019?