Summary of Financial Information Concerning Company's Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Segment Reporting Information [Line Items]
Revenues	$ 489,381		$ 410,731		$ 939,272		$ 787,161
EBITDA	167,994	[1]	127,557	[1]	312,671	[1]	236,132	[1]
Western
Segment Reporting Information [Line Items]
Revenues	202,833		201,544		395,984		382,203
Central
Segment Reporting Information [Line Items]
Revenues	130,434		112,680		245,027		216,510
Eastern
Segment Reporting Information [Line Items]
Revenues	95,725		93,636		183,494		182,673
Exploration and Production
Segment Reporting Information [Line Items]
Revenues	60,389		2,871		114,767		5,775
Operating Segments
Segment Reporting Information [Line Items]
Revenues	556,120		470,740		1,062,879		902,396
EBITDA	168,256		128,245		315,538		243,963
Operating Segments | Western
Segment Reporting Information [Line Items]
Revenues	229,510		227,092		445,856		431,773
EBITDA	62,386	[1]	58,890	[1]	120,962	[1]	112,692	[1]
Operating Segments | Central
Segment Reporting Information [Line Items]
Revenues	147,210		127,805		275,173		244,718
EBITDA	48,517	[1]	40,167	[1]	88,755	[1]	75,617	[1]
Operating Segments | Eastern
Segment Reporting Information [Line Items]
Revenues	115,542		112,972		220,971		220,130
EBITDA	29,029	[1]	27,231	[1]	54,909	[1]	51,766	[1]
Operating Segments | Exploration and Production
Segment Reporting Information [Line Items]
Revenues	63,858		2,871		120,879		5,775
EBITDA	28,324	[1]	1,957	[1]	50,912	[1]	3,888	[1]
Corporate, Non-Segment
Segment Reporting Information [Line Items]
EBITDA	(262)	[1],[2]	(688)	[1],[2]	(2,867)	[1],[2]	(7,831)	[1],[2]
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	(66,739)	[3]	(60,009)	[3]	(123,607)	[3]	(115,235)	[3]
Intersegment Eliminations | Western
Segment Reporting Information [Line Items]
Revenues	(26,677)	[3]	(25,548)	[3]	(49,872)	[3]	(49,570)	[3]
Intersegment Eliminations | Central
Segment Reporting Information [Line Items]
Revenues	(16,776)	[3]	(15,125)	[3]	(30,146)	[3]	(28,208)	[3]
Intersegment Eliminations | Eastern
Segment Reporting Information [Line Items]
Revenues	(19,817)	[3]	(19,336)	[3]	(37,477)	[3]	(37,457)	[3]
Intersegment Eliminations | Exploration and Production
Segment Reporting Information [Line Items]
Revenues	$ (3,469)	[3]			$ (6,112)	[3]

[1] For those items included in the determination of 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 four operating segments.

[3] Intercompany revenues reflect each segment's total intercompany sales, including intercompany sales within a segment and between segments. Transactions within and between segments are generally made on a basis intended to reflect the market value of the service.