The following tables set forth the costs, accumulated amortization and net book value of the Company’s separately identifiable intangible assets as of December 31, 2020 and September 30, 2020 and estimated future amortization expense.

The trade names are amortized on a straight – line basis over their respective estimated useful lives of between five and ten years. Intangible assets that represent customer relationships are amortized on the basis of estimated future undiscounted cash flows or using the straight – line basis over estimated remaining useful lives of five to ten years. Non-compete agreements are amortized based on a straight-line basis over the term of the respective non-compete agreements, which are typically five years in duration.

The amortization expense for intangible assets was $1,044 and $1,398 for three-month periods ended December 31, 2020 and 2019, respectively.