Segment Reporting (Summary of Financial Information Concerning Company's Reportable Segments) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenue	$ 485,877		$ 503,646	$ 489,381	$ 449,892	$ 448,803		$ 425,654	$ 410,731	$ 376,430	$ 1,928,795		$ 1,661,618		$ 1,505,366
EBITDA											651,339	[1]	507,807	[1]	485,819	[1]
Depreciation and amortization											243,864		193,584		167,100
Capital expenditures											209,874		153,517		141,924
Total assets	5,064,252	[2]				5,076,026	[2]				5,064,252	[2]	5,076,026	[2]	3,328,005	[2]
Intercompany Revenues [Member]
Segment Reporting Information [Line Items]
Revenue											249,830	[3]	232,759	[3]	218,612	[3]
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue											2,178,625		1,894,377		1,723,978
EBITDA											651,567		518,880		480,300
Western [Member]
Segment Reporting Information [Line Items]
Revenue											805,790		782,134		742,588
EBITDA											249,548	[1]	229,427	[1]	232,940	[1]
Depreciation and amortization											81,164		78,191		74,628
Capital expenditures											70,960		64,583		57,037
Total assets	1,487,409	[2]				1,507,081	[2]				1,487,409	[2]	1,507,081	[2]	1,370,098	[2]
Western [Member] | Intercompany Revenues [Member]
Segment Reporting Information [Line Items]
Revenue											99,974	[3]	100,094	[3]	98,418	[3]
Western [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue											905,764		882,228		841,006
EBITDA											249,548		229,427		232,940
Central [Member]
Segment Reporting Information [Line Items]
Revenue											510,928		461,875		419,717
EBITDA											182,790	[1]	164,756	[1]	145,088	[1]
Depreciation and amortization											64,165		54,743		48,690
Capital expenditures											57,952		51,300		45,758
Total assets	1,173,089	[2]				1,114,479	[2]				1,173,089	[2]	1,114,479	[2]	995,312	[2]
Central [Member] | Intercompany Revenues [Member]
Segment Reporting Information [Line Items]
Revenue											62,438	[3]	56,041	[3]	51,658	[3]
Central [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue											573,366		517,916		471,375
EBITDA											182,790		164,756		145,088
Eastern [Member]
Segment Reporting Information [Line Items]
Revenue											371,772		366,825		332,601
EBITDA											108,173	[1]	101,046	[1]	95,301	[1]
Depreciation and amortization											51,546		49,289		41,135
Capital expenditures											39,703		32,037		35,139
Total assets	807,124	[2]				826,687	[2]				807,124	[2]	826,687	[2]	841,251	[2]
Eastern [Member] | Intercompany Revenues [Member]
Segment Reporting Information [Line Items]
Revenue											76,072	[3]	75,082	[3]	68,536	[3]
Eastern [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue											447,844		441,907		401,137
EBITDA											108,173		101,046		95,301
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenue											240,305		50,784		10,460	[4],[5]
EBITDA											111,056	[1]	23,651	[1]	6,971	[1],[4],[5]
Depreciation and amortization											44,099		9,018		800	[4],[5]
Capital expenditures											34,916		1,971		705	[4],[5]
Total assets	1,484,501	[2]				1,493,693	[2]				1,484,501	[2]	1,493,693	[2]	45,650	[2],[4],[5]
Exploration and Production [Member] | Intercompany Revenues [Member]
Segment Reporting Information [Line Items]
Revenue											11,346	[3]	1,542	[3]
Exploration and Production [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue											251,651		52,326		10,460	[4],[5]
EBITDA											111,056		23,651		6,971
Corporate [Member]
Segment Reporting Information [Line Items]
EBITDA											(228)	[1],[4],[5]	(11,073)	[1],[4],[5]	5,519	[1]
Depreciation and amortization											2,890	[4],[5]	2,343	[4],[5]	1,847
Capital expenditures											6,343	[4],[5]	3,626	[4],[5]	3,285
Total assets	$ 112,129	[2],[4],[5]				$ 134,086	[2],[4],[5]				$ 112,129	[2],[4],[5]	$ 134,086	[2],[4],[5]	$ 75,694	[2]

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

[2] Goodwill is included within total assets for each of the Company’s 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.

[4] 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.

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