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Income Taxes - Balances of Unrecognized Tax Benefits (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]        
Unrecognized tax benefits $ 36,229 $ 35,240 $ 54,541 $ 50,668
Portion that, if recognized, would reduce tax expense and effective tax rate 35,561 33,128 48,312  
Accrued interest on unrecognized tax benefits 5,368 5,539 8,750  
Accrued penalties on unrecognized tax benefits 631 650 673  
Minimum        
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]        
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months 0 0 0  
Portion that, if recognized, would reduce tax expense and effective tax rate 0 0 0  
Maximum        
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]        
Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months 13,655 12,332 27,485  
Portion that, if recognized, would reduce tax expense and effective tax rate $ 12,483 $ 10,983 $ 24,009