Exploratory Costs (Tables)

9 Months Ended

Sep. 30, 2018

Extractive Industries [Abstract]

Schedule of Capitalized Exploratory Wells

The following table sets forth capitalized exploratory well costs and includes additions pending determination of proved reserves, reclassifications to proved reserves and costs charged to expense:

	Three months ended September 30,						Nine months ended September 30,
(in thousands)	2018			2017			2018			2017
Capitalized exploratory well costs at beginning of period	$	128,234		$	141,401		$	132,200		$	164,996
Additions pending determination of proved reserves	202,743			168,965			578,784			504,668
Reclassifications due to determination of proved reserves	(206,031		)	(174,270		)	(586,038		)	(533,568		)
Capitalized exploratory well costs at end of period	$	124,946		$	136,096		$	124,946		$	136,096

The following table sets forth capitalized exploratory well costs:

(in thousands)	September 30, 2018		December 31, 2017
Exploratory wells in progress (drilling rig not released)	$	17,578	$	10,879
Capitalized exploratory well costs capitalized for a period of one year or less	107,368		121,321
Total capitalized exploratory well costs	$	124,946	$	132,200