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FAIR VALUE OF FINANCIAL INSTRUMENTS (Debt) (Detail) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 949,996 $ 954,348
Estimated Fair Value 959,728 968,514
Industrial revenue bond, due 2023 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value 8,400 8,400
Estimated Fair Value 8,400 8,400
Revolving credit agreement, due 2017 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value 0 0
Estimated Fair Value 0 0
5.51% Senior notes due 2017 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value 150,000 150,000
Estimated Fair Value $ 161,000 162,617
Debt Instrument, Interest Rate, Stated Percentage 5.51%  
3.84% Senior notes due 2021 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 99,988 99,934
Estimated Fair Value $ 99,988 99,934
Debt Instrument, Interest Rate, Stated Percentage 3.84%  
3.70% Senior notes due 2023 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 225,000 225,000
Estimated Fair Value $ 224,473 225,748
Debt Instrument, Interest Rate, Stated Percentage 3.70%  
3.85% Senior notes due 2025 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 97,721 98,360
Estimated Fair Value $ 97,721 98,360
Debt Instrument, Interest Rate, Stated Percentage 3.85%  
4.24% Senior notes due 2026 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 194,733 197,237
Estimated Fair Value $ 194,733 197,237
Debt Instrument, Interest Rate, Stated Percentage 4.24%  
4.05% Senior notes due 2028 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 73,116 74,348
Estimated Fair Value $ 73,116 74,348
Debt Instrument, Interest Rate, Stated Percentage 4.05%  
4.11% Senior Notes [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 100,000 100,000
Estimated Fair Value $ 99,259 100,801
Debt Instrument, Interest Rate, Stated Percentage 4.11%  
Other debt [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying Value $ 1,038 1,069
Estimated Fair Value $ 1,038 $ 1,069