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Long-Term Debt - Long-Term Debt Instrument (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Jan. 15, 2015
Debt Instrument [Line Items]      
Document Period End Date Sep. 30, 2017    
Total current portion of long-term debt $ 120,000 $ 55,500  
Total notes 498,904 598,785  
Long-term credit agreements 370,000 426,250  
Debt Issuance Costs, Gross (8,163) (6,663)  
Total long-term debt 860,741 1,018,372  
Current portion of long-term debt 120,000 55,500  
Total debt 980,741 1,073,872  
Notes Payable, Current 0 500  
5.660% senior notes, Series C, semi-annual interest payments, balloon due 2016      
Debt Instrument [Line Items]      
Current portion of senior notes     $ 25,000
4.500% senior notes, Series E, quarterly interest payments, balloon due 2018      
Debt Instrument [Line Items]      
Total notes 0 100,000  
4.200% senior notes, semi-annual interest payments, net of the unamortized discount, balloon due 2024      
Debt Instrument [Line Items]      
Total notes 498,904 498,785  
5-year term-loan facility, periodic interest and principal payments, LIBOR plus up to 1.750%, expires June 28, 2022      
Debt Instrument [Line Items]      
Current portion of loan facility 20,000 55,000  
Long-term credit agreements 370,000 426,250  
5-year revolving-loan facility, periodic interest payments, currently LIBOR plus up to 1.500%, plus commitment fees up to 0.250%, expires June 28, 2022      
Debt Instrument [Line Items]      
Long-term credit agreements $ 0 $ 0