pre_text: Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): Depreciation expense on property and equipment was $5.0 million, $6.4 million and $7.1 million for the years
  ended December 31, 2019, 2018 and 2017, respectively
table: Useful life (in years) December 31, 2019 December 31, 2018
table: Equipment 1-3 $22,702 $49,804
table: Software 1-3 726 4,088
table: Furniture and fixtures 1-3 459 967
table: Leasehold improvements 2-8 5,440 3,832
table: Construction in progress -- 160
table: Property and equipment, gross 29,327 58,581
table: Less: accumulated depreciation (21,671) (51,589)
table: Property and equipment, net $7,656 $7,262
question: Analyse this data from a financial earnings document. What is the total depreciation expense on property and equipment from 2017 to 2019?