Tax Effect of Significant Temporary Differences Representing Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	$ 47,259	$ 64,443	$ 157,380
Net Change	(17,184)	(92,937)	115,436
Beginning Balance	64,443	157,380	41,944
Ending Balance	67,201	63,580	62,092
Net Change	3,621	1,488	15,189
Beginning Balance	63,580	62,092	46,903
Ending Balance	114,460	128,023	219,472
Net Change	(13,563)	(91,449)	130,625
Beginning Balance	128,023	219,472	88,847
Ending Balance	(955,065)	(920,882)	(848,724)
Net Change	(34,183)	(72,158)	(290,399)
Beginning Balance	(920,882)	(848,724)	(558,325)
Ending Balance	(969,372)	(932,366)	(863,379)
Net Change	(37,006)	(68,987)	(289,925)
Beginning Balance	(932,366)	(863,379)	(573,454)
Ending Balance	(854,912)	(804,343)	(643,907)
Net Change	(50,569)	(160,436)	(159,300)
Beginning Balance	(804,343)	(643,907)	(484,607)
Net Operating Loss Carryforwards
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance		18,914	114,576
Net Change	(18,914)	(95,662)	114,576
Beginning Balance	18,914	114,576
Ending Balance	13,452	11,762	18,434
Net Change	1,690	(6,672)	11,969
Beginning Balance	11,762	18,434	6,465
Workers Compensation Allowance
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	27,612	25,078	24,004
Net Change	2,534	1,074	714
Beginning Balance	25,078	24,004	23,290
Other
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	19,647	20,451	18,800
Net Change	(804)	1,651	146
Beginning Balance	20,451	18,800	18,654
Ending Balance	14,703	15,124	10,670
Net Change	(421)	4,454	(5,361)
Beginning Balance	15,124	10,670	16,031
Ending Balance	(14,307)	(11,484)	(14,655)
Net Change	(2,823)	3,171	474
Beginning Balance	(11,484)	(14,655)	(15,129)
Ending Balance	(15,471)	(15,285)	(12,901)
Net Change	(186)	(2,384)	(1,231)
Beginning Balance	(15,285)	(12,901)	(11,670)
Expense associated with employee stock options
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	16,208	14,672	12,728
Net Change	1,536	1,944	1,476
Beginning Balance	14,672	12,728	11,252
Federal benefit of state deferred tax liabilities
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	22,838	22,022	20,260
Net Change	816	1,762	7,105
Beginning Balance	22,022	20,260	13,155
Property and equipment basis difference
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	(939,594)	(905,597)	(835,823)
Net Change	(33,997)	(69,774)	(289,168)
Beginning Balance	$ (905,597)	$ (835,823)	$ (546,655)