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

6 Months Ended

Jun. 30, 2018

Extractive Industries [Abstract]

Capitalized Costs and Accumulated Depreciation, Depletion and Amortization

	June 30, 2018			December 31, 2017
	(in thousands)
Natural gas and oil properties:
Properties subject to depletion	$	11,067,325		$	10,572,453
Unproved properties		2,599,162			2,644,000
Total		13,666,487			13,216,453
Accumulated depreciation, depletion and amortization		(3,961,365	)		(3,649,716	)
Net capitalized costs	$	9,705,122		$	9,566,737

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