Reconciliation of Primary Measure of Segment Profitability to Income Before Income Tax Provision (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	$ 175,969	[1]	$ 134,434	[1]	$ 488,640	[1]	$ 370,565	[1]
Depreciation	(55,863)		(42,313)		(162,277)		(119,331)
Amortization of intangibles	(6,211)		(6,267)		(18,861)		(18,115)
Gain (loss) on disposal of assets	1,129		(244)		(1,993)		(715)
Loss (gain) on prior office leases	596				(9,902)
Gain from litigation settlement			3,537				3,537
Interest expense	(17,911)		(11,949)		(55,851)		(36,063)
Other income (expense), net	845		825		(119)		1,663
Income before income tax provision	98,554		78,023		239,637		201,541
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	175,781		136,426		491,319		380,388
Operating Segments | Western
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	67,773	[1]	61,119	[1]	188,736	[1]	173,810	[1]
Operating Segments | Central
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	48,845	[1]	47,072	[1]	137,600	[1]	122,688	[1]
Operating Segments | Eastern
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	28,038	[1]	26,113	[1]	82,947	[1]	77,879	[1]
Operating Segments | Exploration and Production
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	31,125	[1]	2,122	[1]	82,036	[1]	6,011	[1]
Corporate, Non-Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
EBITDA	$ 188		$ (1,992)		$ (2,679)		$ (9,823)

[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.