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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2021
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of change in asset retirement obligation During 2021 and 2020, our overall asset retirement obligation changed as follows (in thousands):
20212020
Beginning balance$95,777 $91,251 
Accretion5,725 5,410 
Changes in estimates of existing obligations (1)21,148 (884)
Ending balance$122,650 $95,777 
 
(1)Changes in estimates of existing obligations are primarily due to the annual review process, which considers various factors including inflation rate, current estimates for removal costs, discount rates, and the estimated remaining life of assets. The increase in 2021 is primarily due to a decrease in the discount rate and an increase in the estimated life of the ARO assets.