Long-term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Total debt including current maturities	$ 2,245,247	$ 599,558
Current maturities	(46)	(350,005)
Total long-term debt	2,245,201	249,553
2.50% notes, due 2017, net of unamortized discount of $ 76 at December 31, 2012
Debt Instrument [Line Items]
Notes payable	549,924	0
3.70% notes, due 2022, net of unamortized discount of $ 2,395 at December 31, 2012
Debt Instrument [Line Items]
Notes payable	597,585	0
4.00% notes, due 2022, net of unamortized discount of $ 1,020 at December 31, 2012
Debt Instrument [Line Items]
Notes payable	498,996	0
7.05% notes, due 2029, net of unamortized discount of $ 1,538 at December 31, 2012
Debt Instrument [Line Items]
Notes payable	248,477	248,384
5.125% notes, due 2042, net of unamortized discount of $ 904 at December 31, 2012
Debt Instrument [Line Items]
Notes payable	349,096	0
6.375% notes, due 2012, net of unamortized discount of $ 38 at December 31, 2012
Debt Instrument [Line Items]
Notes payable	0	349,962
Other, 6%, due through 2028
Debt Instrument [Line Items]
Notes payable	$ 1,169	$ 1,212