Significant Commitments by Category (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Minimum Rental Commitments
2017	$ 532
2018	657
2019	637
2020	638
2021	634
Thereafter	159
Total	3,257
Gathering and Intermediate Transportation [Member]
Commitments
Contractual Commitments Future Minimum Payments Due Current	11,702
2018	12,962
2019	12,962
2020	12,962
2021	12,962
Thereafter	50,750
Total	114,300
Other Commitments
Commitments
Contractual Commitments Future Minimum Payments Due Current	254
2018	121
2019	44
2020	0
2021	0
Thereafter	0
Total	419
Contract Drilling [Member]
Commitments
Contractual Commitments Future Minimum Payments Due Current	20,692
2018	0
2019	0
2020	0
2021	0
Thereafter	0
Total	$ 20,692