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Long-Term Debt - Long-Term Debt Instrument (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Jan. 15, 2015
Debt Instrument [Line Items]      
Document Period End Date Mar. 31, 2018    
Total current portion of long-term debt $ 120,000 $ 120,000  
Total notes 498,983 498,943  
Long-term credit agreements 360,000 365,000  
Debt Issuance Costs, Gross (7,435) (7,802)  
Total long-term debt 851,548 856,141  
Current portion of long-term debt 120,000 120,000  
Total debt 971,548 976,141  
4.500% senior notes, Series E, quarterly interest payments, balloon due September 2018      
Debt Instrument [Line Items]      
Current portion of senior notes 100,000 100,000 $ 25,000
4.200% senior notes, semi-annual interest payments, net of the unamortized discount, balloon due 2024      
Debt Instrument [Line Items]      
Total notes 498,983 498,943  
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 20,000  
Long-term credit agreements 360,000 365,000  
5-year revolving-loan facility, periodic interest payments, 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