Senior and Subordinated Debt (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2012	Jan. 31, 2011
Senior Notes
Total Senior Notes	$ 1,009,529	$ 744,683
Senior and Subordinated Debt
Total Senior and Subordinated Debt	1,038,529	773,683
3.625% Puttable Equity-Linked Senior Notes due 2011 [Member]
Senior Notes
Total Senior Notes	0	45,480
3.625% Puttable Equity-Linked Senior Notes due 2014 [Member]
Senior Notes
Total Senior Notes	199,132	198,806
7.625% Senior Notes due 2015 [Member]
Senior Notes
Total Senior Notes	178,253	178,253
5.000% Convertible Senior Notes due 2016 [Member]
Senior Notes
Total Senior Notes	50,000	90,000
6.500% Senior Notes due 2017 [Member]
Senior Notes
Total Senior Notes	132,144	132,144
7.375% Senior Notes due 2034 [Member]
Senior Notes
Total Senior Notes	100,000	100,000
4.250% Convertible Senior Notes due 2018 [Member]
Senior Notes
Total Senior Notes	350,000	0
Subordinate Tax Revenue Bonds due 2013 [Member]
Senior and Subordinated Debt
Subordinate Tax Revenue Bonds due 2013	$ 29,000	$ 29,000