Senior and Subordinated Debt (Details) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2012	Jan. 31, 2012
Senior Notes
Total Senior Notes	$ 1,128,666	$ 1,009,529
Senior and Subordinated Debt
Senior and Subordinated debt	1,157,666	1,038,529
3.625% Puttable Equity-Linked Senior Notes due 2014 [Member]
Senior Notes
Total Senior Notes	199,294	199,132
Senior note interest rate	3.625%	3.625%
7.625% Senior Notes due 2015 [Member]
Senior Notes
Total Senior Notes	178,253	178,253
Senior note interest rate	7.625%	7.625%
5.000% Convertible Senior Notes due 2016 [Member]
Senior Notes
Total Senior Notes	50,000	50,000
Senior note interest rate	5.00%	5.00%
6.500% Senior Notes due 2017 [Member]
Senior Notes
Total Senior Notes	132,144	132,144
Senior note interest rate	6.50%	6.50%
4.250% Convertible Senior Notes due 2018 [Member]
Senior Notes
Total Senior Notes	350,000	350,000
Senior note interest rate	4.25%	4.25%
7.375% Senior Notes due 2034 [Member]
Senior Notes
Total Senior Notes	218,975	100,000
Senior note interest rate	7.375%	7.375%
Subordinate Tax Revenue Bonds due 2013 [Member]
Senior and Subordinated Debt
Subordinate Tax Revenue Bonds due 2013	$ 29,000	$ 29,000