Supplemental Guarantor Information (Details)	12 Months Ended
	Dec. 31, 2012
Supplemental Guarantor Information
Percentage ownership of Guarantor Subsidiaries	100.00%
5.4 percent senior notes due January 2015
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	5.40%
8.4 percent senior notes due May 2017
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	8.40%
1.6 percent convertible senior notes due May 2018
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	1.60%
6.6 percent senior notes due May 2020
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	6.60%
5.4 percent senior notes due October 2022
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	5.40%