XML 71 R61.htm IDEA: XBRL DOCUMENT v3.21.2
Asset Retirement Obligations (Detail)
$ in Thousands
6 Months Ended
Jun. 30, 2021
USD ($)
Asset Retirement Obligation Disclosure [Abstract]  
Asset retirement obligation liabilities expected, present value $ 26,400
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]  
Asset retirement obligations, beginning balance 14,020
Accretion expense 777
Asset retirement obligations, ending balance 14,797
Financial assurance in form of surety bond $ 28,200