Segment Reporting (Reconciliation of Primary Measure of Segment Profitability to Income before Income Tax Provision) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Segment EBITDA	[1]	$ 943,888		$ 702,394		$ 711,304
Depreciation		(393,600)		(240,357)		(230,944)
Amortization of intangibles		(70,312)		(29,077)		(27,000)
Impairments and other operating items		(27,678)		(494,492)		(4,091)
Interest expense		(92,709)		(64,236)		(64,674)
Other income (expense), net		655		(518)		1,067
Foreign currency transaction gain (loss)		1,121
Income (loss) before income tax provision		361,365		(126,286)		385,662
Operating Segments [Member]
Segment EBITDA		1,063,103		700,461		718,738
Southern [Member]
Segment EBITDA	[1]	163,320		35,718		32,539
Southern [Member] | Operating Segments [Member]
Segment EBITDA		163,320		35,718		32,539
Western [Member]
Segment EBITDA	[1]	315,708		290,937		258,126
Western [Member] | Operating Segments [Member]
Segment EBITDA		315,708		290,937		258,126
Eastern [Member]
Segment EBITDA	[1]	193,361		119,668		104,224
Eastern [Member] | Operating Segments [Member]
Segment EBITDA		193,361		119,668		104,224
Canada [Member]
Segment EBITDA	[1]	149,305
Canada [Member] | Operating Segments [Member]
Segment EBITDA		149,305
Central [Member]
Segment EBITDA	[1]	208,930	[2],[3]	184,006		175,935	[2],[3]
Central [Member] | Operating Segments [Member]
Segment EBITDA		208,930		184,006		175,935
Exploration and Production [Member]
Segment EBITDA	[1]	32,479		70,132	[2],[3]	147,914
Exploration and Production [Member] | Operating Segments [Member]
Segment EBITDA		32,479		70,132		147,914
Corporate [Member]
Segment EBITDA	[1],[2],[3]	$ (119,215)		$ 1,933		$ (7,434)

[1] For those items included in the determination of segment EBITDA, the accounting policies of the segments are the same as those described in Note 1.

[2] Corporate assets include cash, net deferred tax assets, debt issuance costs, equity investments, and corporate facility leasehold improvements and equipment.

[3] Corporate functions include accounting, legal, tax, treasury, information technology, risk management, human resources, training and other administrative functions. Amounts reflected are net of allocations to the six operating segments.