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Tax Effect of Significant Temporary Differences Representing Deferred Tax Assets and Liabilities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Deferred tax assets:    
Net operating loss carryforwards $ 324,389 $ 275,402
Tax credits 6,404 9,053
Expense associated with stock options and restricted stock 13,375 12,126
Workers' compensation allowance 19,900 19,323
Other 22,423 25,891
Total deferred tax assets, gross 386,491 341,795
Allowance to reduce deferred tax asset to expected realizable value (13,232)  
Total deferred tax assets, net 373,259 341,795
Deferred tax liabilities:    
Property and equipment basis difference (669,196) (678,093)
Other (10,224) (10,663)
Total deferred tax liabilities (679,420) (688,756)
Net deferred tax liability $ (306,161) $ (346,961)