Segment Reporting (Reconciliation of Primary Measure of Segment Profitability to Income Before Income Tax Provision) (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Segment EBITDA	$ 386,685	[1]	$ 363,319	[1]	$ 735,706	$ 682,154
Depreciation	(142,450)		(132,827)		(275,634)	(258,067)
Amortization of intangibles	(26,474)		(24,762)		(52,573)	(50,272)
Impairments and other operating items	(7,073)		1,180		(8,104)	(140,501)
Interest expense	(32,426)		(31,160)		(64,796)	(60,291)
Interest income	1,056		1,026		2,210	1,474
Other income, net	2,031		834		1,644	1,852
Foreign currency transaction gain (loss)	30		(1,048)		(190)	(1,638)
Income before income tax provision	181,379		176,562		338,263	174,711
Southern [Member]
Segment EBITDA	68,787	[1]	67,168	[1]	137,694	136,108
Western [Member]
Segment EBITDA	81,175	[1]	87,045	[1]	153,832	162,613
Eastern [Member]
Segment EBITDA	74,795	[1]	70,668	[1]	142,229	135,297
Canada [Member]
Segment EBITDA	67,305	[1]	67,792	[1]	126,571	125,914
Central [Member]
Segment EBITDA	63,132	[1],[2]	60,716	[1],[2]	121,553	113,368
Exploration and Production [Member]
Segment EBITDA	31,231	[1]	21,092	[1]	59,910	35,637
Corporate [Member]
Segment EBITDA	260	[1],[2]	(11,162)	[1],[2]	(6,083)	(26,783)
Reportable Segments [Member]
Segment EBITDA	$ 386,425		$ 374,481		$ 741,789	$ 708,937

[1] For those items included in the determination of segment EBITDA, the accounting policies of the segments are the same as those described in the Company's most recent Annual Report on Form 10-K.

[2] 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.