Intangibles and Goodwill
 3 Months Ended
Mar. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]  
Intangibles and Goodwill Intangibles and Goodwill
The balance of goodwill was $309.6 million as of March 31, 2020 and December 31, 2019, as no changes occurred during the period.

The following is a summary of amortizable intangible assets as of March 31, 2020 and December 31, 2019 (in thousands):
 March 31, 2020December 31, 2019
CostAccumulated AmortizationNetCostAccumulated AmortizationNet
Customer relationships$150,239  $(69,680) $80,559  $150,239  $(67,317) $82,922  
Carrier relationships18,300  (5,203) 13,097  18,300  (4,934) 13,366  
Non-compete agreements5,239  (3,952) 1,287  5,239  (3,765) 1,474  
Trade names5,640  (5,640) —  5,640  (5,640) —  
$179,418  $(84,474) $94,944  $179,418  $(81,656) $97,762  
Note: Amounts may not foot due to rounding.

The customer relationships are being amortized using an accelerated method over their estimated weighted-average useful life of 14.8 years, as an accelerated method best approximates the distribution of cash flows generated by the acquired customer relationships. The carrier relationships, non-compete agreements and trade names are being amortized using the straight-line method over their estimated weighted-average useful lives of 17.0 years, 6.7 years and 4.0 years, respectively. Amortization expense related to intangible assets was $2.8 million and $3.2 million for the three months ended March 31, 2020 and 2019, respectively.

The estimated amortization expense for the next five years and thereafter is as follows (in thousands):
Remainder of 2020  $8,155  
2021  10,362  
2022  10,005  
2023  9,501  
20248,897  
Thereafter48,023  
Total$94,944  
Note: Amounts may not foot due to rounding.