Long term debt (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Total notes payable	$ 2,600,000	$ 2,251,169
Unamortized discount on notes payable	(5,439)	(5,922)
Total notes payable, net of unamortized discount	2,594,561	2,245,247
Capitalized lease obligation	368,251	0
Total debt including current maturities	2,962,812	2,245,247
Current maturities	(26,249)	(46)
Total long-term debt	2,936,563	2,245,201
2.50% notes, due 2017 [Member]
Debt Instrument [Line Items]
Notes payable	550,000	550,000
3.70% notes, due 2022 [Member]
Debt Instrument [Line Items]
Notes payable	600,000	600,000
4.00% notes, due 2022 [Member]
Debt Instrument [Line Items]
Notes payable	500,000	500,000
7.05% notes, due 2029 [Member]
Debt Instrument [Line Items]
Notes payable	250,000	250,000
5.125% notes, due 2042 [Member]
Debt Instrument [Line Items]
Notes payable	350,000	350,000
Notes payable to banks, 1.4375% at December 31, 2013 [Member]
Debt Instrument [Line Items]
Notes payable	350,000	0
Other, 6%, due through 2028 [Member]
Debt Instrument [Line Items]
Notes payable	$ 0	$ 1,169