v3.19.3.a.u2
INTANGIBLE ASSETS
 12 Months Ended
Dec. 31, 2019
Intangible Assets, Net (Excluding Goodwill) [Abstract]  
INTANGIBLE ASSETS INTANGIBLE ASSETS

Intangible assets consisted of the following:
 
Weighted-Average Amortization Period
 
December 31, 2019
 
December 31, 2018
 
 
Cost
 
Accumulated
Amortization
 
Cost
 
Accumulated
Amortization
 
(Years)
 
(Thousands of Dollars)
Customer contracts and relationships
18
 
$
863,900

 
$
(183,832
)
 
$
863,950

 
$
(132,509
)
Other
47
 
2,359

 
(795
)
 
2,359

 
(744
)
Total
 
 
$
866,259

 
$
(184,627
)
 
$
866,309

 
$
(133,253
)

Intangible assets are recorded at fair value as of the date acquired. All of our intangible assets are amortized on a straight-line basis. Amortization expense for intangible assets was $51.4 million, $51.4 million and $39.6 million for the years ended December 31, 2019, 2018 and 2017, respectively. The estimated aggregate amortization expense is approximately $51.0 million for each of the years 2020 through 2022, and approximately $45.0 million for 2023 and 2024.