AROs (Tables)

6 Months Ended

Jun. 30, 2019

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Changes in AROs

The following table presents the changes in AROs as recorded in other long-term liabilities in the unaudited condensed consolidated balance sheets:

	As of June 30,
	2019			2018
	(in thousands)
Balance at beginning of period	$	20,033		$	15,347
Additional obligations incurred	1,755			2,041
Accretion expense	640			613
Other	(21		)	(13		)
Balance at end of period	$	22,407		$	17,988