Senior and Subordinated Debt (Details 1) (USD $)	Jul. 31, 2011	Jan. 31, 2011
Schedule of carrying amounts of the debt and equity balances
Net carrying amount of the puttable equity-linked senior notes	$ 1,055,831,000	$ 744,683,000
Senior notes due 2011 [Member]
Schedule of carrying amounts of the debt and equity balances
Carrying amount of equity component	7,484,000	7,484,000
Outstanding principal amount of the puttable equity-linked senior notes	46,891,000	46,891,000
Unamortized discount	(425,000)	(1,411,000)
Net carrying amount of the puttable equity-linked senior notes	$ 46,466,000	$ 45,480,000