XML 59 R42.htm IDEA: XBRL DOCUMENT v3.19.1
ASSET RETIREMENT OBLIGATIONS AND RESTRICTED CASH - Schedule of Restricted Cash and Cash Equivalents (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Restricted Cash And Cash Equivalents [Roll Forward]      
Restricted cash, beginning of period $ 19,652 $ 22,127  
Additional collateral posted 0   $ 117
Release of collateral related to change in surety agents 30 $ (2,592)  
Restricted cash, end of period $ 19,682