ASSET RETIREMENT OBLIGATION

12 Months Ended

Dec. 31, 2019

Asset Retirement Obligation Disclosure [Abstract]

We recognize an estimated liability for future costs associated with the abandonment and reclamation of our mining properties. A liability for the fair value of an asset retirement obligation and a corresponding increase to the carrying value of the related long-lived asset are recorded as the mining operations occur or the assets are acquired.

Our asset retirement obligation is based on the estimated cost to abandon and reclaim the mining operations, the economic life of the properties, and federal and state regulatory requirements. The liability is discounted using credit adjusted risk-free rate estimates at the time the liability is incurred or when there are upward revisions to estimated costs. The credit adjusted risk-free rates used to discount our abandonment liabilities range from 6.9% to 9.7%. Revisions to the liability occur due to construction of new or expanded facilities, changes in estimated abandonment costs or economic lives, changes in the estimated timing of the reclamation activities or if federal or state regulators enact new requirements regarding the abandonment or reclamation of mines.

Following is a table of the changes to our asset retirement obligations for the following periods (in thousands):



	Year Ended December 31,
	2019			2018			2017
Asset retirement obligation, at beginning of period	$	23,125		$	21,476		$	19,976
Liabilities settled	(38		)	(19		)	—
Liabilities incurred	60			—			29
Changes in estimated obligations	(2,690		)	—			(87		)
Accretion of discount	1,793			1,668			1,558
Total asset retirement obligation, at end of period	$	22,250		$	23,125		$	21,476

As of December 31, 2019, $0.1 million of the total asset retirement obligation is included in "Other current liabilities" on the Consolidated Balance Sheets. We estimate approximately $9.9 million in payments may occur in the next five years.