Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Summary of Activity for ARO Liabilities (Detail)

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Commitments and Contingencies - Summary of Activity for ARO Liabilities (Detail)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Commitments And Contingencies Disclosure [Abstract]  
Balance as of December 31, 2017 $ 580
Liabilities incurred during the period 88
Balance as of March 31, 2018 $ 668