Tax Effect of Significant Temporary Differences Representing Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	$ 77,926	$ 50,706	$ 47,259
Net Change	27,220	3,447	(17,184)
Beginning Balance	50,706	47,259	64,443
Ending Balance	137,031	66,916	67,201
Net Change	70,115	(285)	3,621
Beginning Balance	66,916	67,201	63,580
Ending Balance	214,354	117,622	114,460
Net Change	96,732	3,162	(13,563)
Beginning Balance	117,622	114,460	128,023
Ending Balance	(1,000,261)	(1,002,576)	(955,065)
Net Change	2,315	(47,511)	(34,183)
Beginning Balance	(1,002,576)	(955,065)	(920,882)
Ending Balance	(1,013,066)	(1,016,207)	(969,372)
Net Change	3,141	(46,835)	(37,006)
Beginning Balance	(1,016,207)	(969,372)	(932,366)
Ending Balance	(798,712)	(898,585)	(854,912)
Net Change	99,873	(43,673)	(50,569)
Beginning Balance	(898,585)	(854,912)	(804,343)
Allowance to reduce deferred tax asset to expected realizable value, Net Change	(603)
December 31,	(603)
Net Operating Loss Carryforwards
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	27,887
Net Change	27,887		(18,914)
Beginning Balance			18,914
Ending Balance	77,514	12,464	13,452
Net Change	65,050	(988)	1,690
Beginning Balance	12,464	13,452	11,762
Workers Compensation Allowance
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	28,734	28,310	27,612
Net Change	424	698	2,534
Beginning Balance	28,310	27,612	25,078
Other
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	21,305	22,396	19,647
Net Change	(1,091)	2,749	(804)
Beginning Balance	22,396	19,647	20,451
Ending Balance	20,441	16,047	14,703
Net Change	4,394	1,344	(421)
Beginning Balance	16,047	14,703	15,124
Ending Balance	(12,805)	(13,631)	(14,307)
Net Change	826	676	(2,823)
Beginning Balance	(13,631)	(14,307)	(11,484)
Ending Balance	(13,339)	(15,623)	(15,471)
Net Change	2,284	(152)	(186)
Beginning Balance	(15,623)	(15,471)	(15,285)
Expense associated with employee stock options
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	14,591	14,386	16,208
Net Change	205	(1,822)	1,536
Beginning Balance	14,386	16,208	14,672
Federal benefit of state deferred tax liabilities
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	24,485	24,019	22,838
Net Change	466	1,181	816
Beginning Balance	24,019	22,838	22,022
Property and equipment basis difference
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Ending Balance	(986,922)	(986,953)	(939,594)
Net Change	31	(47,359)	(33,997)
Beginning Balance	$ (986,953)	$ (939,594)	$ (905,597)