Income Taxes (Details 2) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013	Jan. 31, 2012
Components of deferred income tax liability
Net deferred tax liability	$ 474,406	$ 433,040
Temporary Differences [Member]
Components of deferred income tax liability
Depreciation	493,489	430,713
Capitalized costs	1,018,375	1,043,938
Tax loss carryforward	(161,758)	(115,385)
State loss carryforward, net of federal benefit	0	0
Valuation allowance	0	0
Federal tax credits and other carryforwards	0	0
Other comprehensive loss	(168,585)	(196,775)
Basis in unconsolidated entities	199,359	156,445
Other	(83,747)	(130,378)
Net deferred tax liability	1,297,133	1,188,558
Deferred Tax [Member]
Components of deferred income tax liability
Depreciation	191,390	167,043
Capitalized costs	394,956	404,871
Tax loss carryforward	(56,615)	(40,385)
State loss carryforward, net of federal benefit	(23,974)	(25,473)
Valuation allowance	53,282	55,330
Federal tax credits and other carryforwards	(58,094)	(57,503)
Other comprehensive loss	(65,382)	(76,315)
Basis in unconsolidated entities	77,317	60,674
Other	(38,474)	(55,202)
Net deferred tax liability	$ 474,406	$ 433,040