Supplemental Guarantor Information (Details)	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
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%
0.25 percent convertible senior notes due June 2019
Interest rate on obligations of the parent, guaranteed by the Guarantor Subsidiaries
Interest rate stated percentage	0.25%	0.25%	0.25%
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%