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ASSET RETIREMENT OBLIGATIONS AND RESTRICTED CASH - Schedule of Restricted Cash and Cash Equivalents (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Restricted Cash And Cash Equivalents [Roll Forward]    
Restricted cash, beginning of period $ 23,175 $ 12,980
Restricted cash from acquisitions 0 4,532
Additional collateral posted 0 5,663
Release of collateral related to change in surety agents (13,111) 0
Posting of collateral with new surety agents 12,743 0
Restricted cash, end of period $ 22,807 $ 23,175