Capitalized Costs and Accumulated Depreciation, Depletion and Amortization (Tables)

3 Months Ended

Mar. 31, 2018

Extractive Industries [Abstract]

Capitalized Costs and Accumulated Depreciation, Depletion and Amortization

	March 31, 2018			December 31, 2017
	(in thousands)
Natural gas and oil properties:
Properties subject to depletion	$	10,808,673		$	10,572,453
Unproved properties		2,648,981			2,644,000
Total		13,457,654			13,216,453
Accumulated depreciation, depletion and amortization		(3,807,356	)		(3,649,716	)
Net capitalized costs	$	9,650,298		$	9,566,737

^(a) Includes capitalized asset retirement costs and the associated accumulated amortization.