Asset Retirement Obligations - Schedule of Asset Retirement Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations Acquisition of Properties		$ 8,700
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning of period	$ 17,586	11,238	$ 15,176
Liabilities incurred (1)(2)	10,649	10,683	83
Liabilities settled	(1,630)	(1,063)	(16)
Disposition of properties	(351)	(5,138)	(4,840)
Accretion expense	1,291	972	861
Revisions to estimate	2,110	894	(26)
End of period	29,655	17,586	11,238
Less: Current asset retirement obligations	2,325	1,489	535
Long-term asset retirement obligations	$ 27,330	$ 16,097	$ 10,703